This is the 4 th article in a series on some new research on bullet jumps. Here is a recap of the previous articles in the series:
In this post, I’ll share more research data Mark has collected related to bullet jumps for two popular bullets used for long range:
If you missed the previous post, I’d strongly recommend you start there – or this simply won’t make sense. I carefully explained the testing methods and data/charts in the last post and won’t be repeating that info again here.
Fundamentally, this research wasn’t focused on finding the specific bullet jump that provides the absolute best precision (i.e. smallest possible group), but was focused on finding the best precision over a range bullet jumps. We are looking for the window of bullet jumps that would continue to have a similar point of impact over 200+ rounds, without having to adjust the seating depth as the lands of the barrel erode. That means the rifle would be more consistent from the start of the match to the end of it or could shoot a particular kind of match-grade factory ammo really well for a longer period of time.
Here is a visual that illustrates what we’re looking for, which is the big green area that provides both very good precision AND is also very forgiving in terms of bullet jump/seating depth.
This research isn’t saying you can’t get good groups close the lands – many obviously do! But, could we get really good groups AND not have to frequently adjust the seating depth of our bullet? That’s the question this research is exploring.
The last post focused on Berger’s 6mm 105 Hybrid, but Mark has also compiled quite a bit of data on the 6.5mm Hornady 147 gr. ELD Match bullet. Before we dive into the complete results for that bullet, I’d like to start by looking at a unique aspect of the bullet jump tests Mark conducted with the Hornady 147 gr. ELD-M.
A portion of how Mark tested the 147gr ELDM was in three different ways using the same exact rifle. The custom rifle he used for these three tests was a 6.5 Creedmoor in a Defiance Elite action in a McRee chassis with a 26” Bartlein Heavy Palma contour 1:8” twist barrel and a TBAC Ultra-7 suppressor. They ran through the 20-shot bullet jump test, from 0.000″ jump (a.k.a. “kissing the lands”) to a 0.095″ bullet jump in 0.005″ increments, with that one rifle and varied:
So this was basically side-by-side testing for the same rifle and bullet over a 60-shot sample size and with some variation introduced. Mark obviously shoots a lot, but the other two shooters are accomplished PRS/NRL competitors who regularly place in the top 10 at major matches.
Let’s look at the results for the vertical POI shift each of them recorded on Mark’s electronic target system at 600 yards based on the distance the 147 gr. ELDM was jumping to the lands of the barrel. The chart below shows the combined data for all three tests.
If this is the first time you’re seeing a chart like this, I’d suggest going back to read the previous article to understand what it represents.
Remember, on this chart the flatter the line the better. If a line is steep, that means there was significant vertical Point of Impact (POI) shift over a narrow range of bullet jumps (i.e. the bullet seems to be very sensitive to seating depth near that bullet jump). Mid-size cartridges like this can erode by 0.005” in just 100 rounds (read more on that), so where the lines are steep means you could experience measurable vertical stringing in 100 rounds or less. However, if we can find a section where the lines are flatter, that means the vertical POI didn’t change significantly over that range of bullet jumps. For example, look at the area around 0.055-0.065”. Even with different loads, different order of shots, and different shooters, all 3 tests show very little vertical POI shift over that window of bullet jumps.
You can see that regardless of the shooter, order the shots were fired in, or the specific load used, there appears to be a sweet spot around 0.060” of bullet jump, because all of the lines on the chart appear to flatten out near that area. Also, we can see on the chart above that there doesn’t appear to be anything less than 0.040” of jump that seems to be forgiving, and 0.050-0.070” appears to be best for the rifle that was tested … regardless of shooter or specific load.
And while each of the 3 tests only included 1 shot for each of the bullet jumps, it is interesting to see the commonalities in the patterns. There seems to be very few places on the chart where if one of them is shifting up or down in vertical, the other two aren’t also doing that same thing, except possibly to more or less of a degree. The peaks and valleys may not perfectly line up, but they certainly seem to come close in a few spots!
I noticed a recent forum post on AccurateShooter.com of a discussion related to my previous article and Alex Wheeler, owner of Wheeler Accuracy and a respected gunsmith who has built some of the best shooting 1000 yard Benchrest & F-Class rifles, said something that seems relevant to these three tests. The discussion was around tuning loads and finding the ideal seating depth/bullet jump, and here is what Alex said:
“From my experience powder charge will not drastically effect the correct seating depth. Meaning if you change your powder charge the gun will not go from preferring a .010 jump to a .060 jump. It may move a few thousandths, but I think you can use any powder charge you want to rough in on seating depth.” – Alex Wheeler
It seems like the results here, which are based on 3 different loads, seem to corroborate Alex’s experience. If you would have ran through this test with any of those loads, you would likely land at a similar bullet jump.
There was one more quote from Alex in that forum conversation, which is a timely reminder:
“I talked with Mark about his testing a few months ago. Keep in mind he is looking for the widest tune not necessarily the tiniest group. That’s not to say you may not also find the tiniest group at those jumps. Just know what his goal was with this testing. I do think he did a very good job of achieving it.” – Alex Wheeler
Well said, Alex! By the way, Alex is the only other person I’ve seen present an accurate and repeatable method to measure the distance to the rifle lands on your barrel (watch it here), so I know he is someone who believes in the importance of tuning seating depth and has likely done a lot of precise testing himself.
Okay, that was just a sample size of 3 tests (60 shots total), so now let’s look at the complete data Mark has compiled so far with the Hornady 6.5 147 gr. ELD-M. We’ll include the 3 tests above, and we’ll add 6 more rifle/load configurations, including rifles chambered in 6.5 Creedmoor, 6.5 PRC, and 6.5×47 Lapua:
Let’s dive into the vertical POI shift measured for each of those configurations at 600 yards:
That same area around 0.055-0.060” of bullet jump appears to still be a sweet spot for most of these rifles/load configurations. Most all of the various rifle cartridges, loads, and rifle configurations have relatively flat sections near that window of bullet jumps. Compare what is happening there to the spikes and erratic POI shifts that seem to happen closer to the lands on the left side of the chart. There are several rifles that seem to have significant vertical stringing for those jumps that are closer to the lands.
Keep in mind this doesn’t mean the rifles don’t group well at those closer bullet jumps. For example, let’s look at the first red spike, which occurs around 0.015” jump and is related to rifle configuration #8, which is one of the 6.5 PRC rifles. The chart isn’t saying the rifle’s groups measured 0.8 MOA at that jump. It might group phenomenally well at that bullet jump – maybe even under 0.2 MOA. We don’t know, because that isn’t what Mark was trying to test. What we can see in the chart above is the shot with a 0.015” bullet jump hit 0.8 MOA above the absolute center of all 20 shots for rifle #8. Then the very next shot, with an identical load in the same rifle but with a 0.020” bullet jump, hit closer to 0.2 MOA above the center of the group, meaning that shot shifted 0.6 MOA down with only a 0.005” of change in bullet jump. Now, for each configuration there is only one shot for each bullet jump, so we shouldn’t try to draw meaningful conclusions from that small of a sample size. But the chart above contains 180 shots/data points in total, and it appears that some of the erratic shifts in vertical are localized in few distinct areas. There are many spikes and steep lines up and down on the left side of the chart for multiple rifles, but there are relatively few on the right side of the chart for any of the rifles. This tells us that Hornady’s 147 gr. ELDM bullet seems to be more forgiving of changes in bullet jump when you are using 0.050” or more of bullet jump, and that appears to be true over a wide range of rifles tested.
Now let’s analyze the data a different way. The chart below takes the same data as above (180 individual shots in a variety of rifle/load configurations) but helps us visualize it in a way that is closer to the crux of what we’re looking for. To get the data below, we looked across all 9 rifle/load configurations shooting the Hornady 147 gr. ELDM and calculated the vertical extreme spread over a rolling window of 3 sequential bullet jumps. Each column represents a bullet jump window that is 0.010 inches wide, which is approximately what you’d expect the lands of the barrel to erode over 200 rounds for popular precision rifle cartridges. For example, the first column on the left below represents the extreme spread for the vertical POI over 3 incremental bullet jumps: 0.000, 0.005, and 0.010 inches. I calculated the vertical extreme spread over those 3 bullet jumps for each configuration, and then averaged those values across all 9 rifle/load configurations so we could see over-arching trends.
On the chart above, the shorter the column the better. For example, 0.050-0.060” and 0.055-0.065” bullet jump ranges were the two windows that had the most consistent vertical POI. Both of those bullet jump ranges averaged a 0.26 MOA vertical extreme spread at 600 yards over all 9 rifle/load configurations tested! That means they provide outstanding precision, and are very forgiving in terms of bullet jump and the distance to the lands. (It also means there were some very consistent shooters behind those rifles!)
Now let’s widen that window from 3 to 5 sequential bullet jumps, to see if there is still a similar pattern. Each column below equates to a range of bullet jumps that spans 0.020”, which would be about what you could expect to happen over around 400 rounds in popular mid-sized cartridges used in PRS/NRL style matches. How quickly the barrel erodes can vary even for the same cartridge depending on how hot your load is, the quality of the steel in your barrel, how long you allow the barrel to cool between strings, and a dozen other factors, so your mileage may vary. Your rifle lands might actually erode by 0.020” over 200 rounds or it could be 600, but I’m simply trying to give general context for what a 0.020” span of bullet jumps represents.
This chart above seems to tell a similar story compared to the previous one, although the “optimal” area we saw before around 0.045-0.070” is less pronounced after we doubled the size of the window of bullet jumps we were analyzing. Of course, we are still talking an extreme spread of 0.45 MOA over a 0.020” window. Again, that doesn’t mean groups averaged 0.45 MOA in that range, but just that average vertical POI didn’t shift by more than over that entire range for all the rifles/loads tested. It’s possible that groups at any point might be very small (or not), but the areas with lower numbers on these charts simply wouldn’t shift significantly as your lands eroded by 0.020” and bullet jump naturally increased by that amount.
Now, let’s look at a very popular 6mm bullet, David Tubb’s 115 gr. DTAC RBT Closed Nose bullet. This is a bullet that David Tubb designed, and it is manufactured to his specs by Sierra Bullets.
For the 115 DTAC bullet, we have a sample size of 6 different rifles that were tested. One interesting aspect of the setups tested for the 115 DTAC is that all of them used a different action. Here are the details of all six configurations:
The chart below shows the combined data, which is for 20 different shots in 0.005” increments from kissing the lands (i.e. 0.000”) up to 0.095” of bullet jump for each of those 6 rifles. So, it represents 120 shots fired with the 115 DTAC.
I’ve been looking at these kinds of charts for a few months now, and it is still tough for me to decipher patterns in this one. I highlighted a couple of ranges that might be slightly flatter than other portions of the chart. The only obvious thing is there seems to be a lot of vertical shift around 0.020-0.040″ for a few of the rifles.
Let’s look at the other types of charts that are based on the same data, and maybe they’ll give us a clearer picture of what windows of bullet jumps seem to be the most forgiving in terms of vertical POI shift.
The chart above makes a couple of ranges of bullet jumps pop out. 0.040-0.050” bullet jumps appear to have minimal vertical shift. It also looks like most bullet jumps beyond 0.070” also provided consistent vertical POI over a wide range of bullet jumps. However, there are a couple of big spikes in the data that show an average shift in vertical of 0.6 MOA or more. The data appears to be saying the 115 DTAC is more sensitive to seating depth, at least across the rifles that were tested here. However, once you get beyond 0.070” of bullet jump, the bullet seems to become very insensitive to seating depth. In other words, the 115 DTAC only appears to be sensitive to seating depth when seating it very close to the lands, but not when you’re jumping it 0.070” or more.
Now let’s look at how consistent the vertical POI is over a window of bullet jumps that is twice as wide:
That “sweet spot” that appeared around 0.040-0.050” bullet jumps in the previous chart seems to have vanished, meaning the sweet spot must not have been 0.020” wide. So while you might not experience vertical stringing in that range of bullet jumps over 0.010” of change in bullet jumps (around 200 rounds of barrel wear with popular mid-sized cartridges), if you pushed beyond that without adjusting your seating depth, the data suggests you’d be more likely to experience a vertical POI shift.
Honestly, you can see that by 0.030-0.050”, it drops off and pretty much gets smaller as you move further and further from the lands. Once you get to a range like 0.060-0.080”, you have an average vertical shift that is less than 0.5 MOA over a 0.020” window of bullet jumps. Remember, that doesn’t mean the rifle ever shoots groups that big, but just that the center POI of your groups wouldn’t likely change by more than that over 300-500 rounds (i.e. it is more forgiving in changes in seating depth or the lands eroding over time).
While Mark has done preliminary testing on a few other bullets, the Berger 105 Hybrid, Hornady 147 ELDM, and Tubb 115 DTAC represent the ones he has compiled the largest sample sizes for so far. The data Mark collected for these three bullets helps us understand how these “sweet spots” can vary based from one bullet design to another. It also seemed to show that for a particular bullet there seems to be commonalities in terms of what range of jumps are most forgiving even over several different combinations of rifles, cartridges, loads, shot order, and shooters.
While there are slightly different patterns between each of the bullets, it does appear none of the bullets showed to have a forgiving bullet jump under about 0.040”. The most consistent vertical POI over a wide range of bullet jumps usually appeared to be closer to 0.060”. Jumps that have been traditionally seen as absurdly long, like 0.080” or more, actually seem to produce less vertical shift in POI as the barrel wears than when the bullet is seated very close to the lands.
Of course, if you tightly manage your seating depth and adjust it regularly (e.g. every 100-200 rounds), then you can still get extremely precise groups seated close to the lands. That is a really important point. None of this research is trying to say you can’t get tiny groups jumping 0.020” or less, or even seated into the lands. Those minimal jumps could produce smaller groups than if you were jumping 0.060” or more, although that isn’t necessarily a hard and fast rule either. What this research seems to show is that when you are seated close to the lands, your load may not be as forgiving in terms of changes to the bullet jump as your barrel wears and you could experience a vertical shift in your zero if you don’t regularly adjust your seating depth.
The next article will be the final post in this series, and will include some information from other shooters on their experience and how they’ve integrated this into their load development process. Stay tuned!
Share On Facebook
Help spread the word about this new research by sharing the post on social media.
Cal Zant is the shooter/author behind PrecisionRifleBlog.com. Cal is a life-long learner, and loves to help others get into this sport he's so passionate about. Cal has an engineering background, unique data-driven approach, and the ability to present technical information in an unbiased and straight-forward fashion. For more info, check out PrecisionRifleBlog.com/About.
If you only read one article in this series, MAKE IT THIS ONE! This article takes all the data collected over months of live-fire research and sums it all up by ranking each type of ammo by hit probability from 400 to 1,200 yards! After all, the size of a group on paper at 100 yards or the muzzle velocity our chronograph spits out doesn’t really matter – at least not directly. For long-range work, all that actually matters is if our bullet impacts the target downrange. Precision and velocity affect that, but so do a lot of other factors! So this article is like the grand finale and ranks which ammo gives us the best odds of connecting with long-range targets.
Seth, I would love to have the chance to test them as well, however with my current schedule, I won’t be able to do either of them any time soon. All of the shooting that we have performed has been funded by Short Action Customs. So it is not like I’m getting paid to do these tests or getting sponsored help with all the loading and components. Maybe this summer I can free up some more time to keep testing.
I am really curious to hear what you guys found out about the 110smk. It is the most notoriously finicky bullet in this game. I have shot close to 1000 of them in multiple cartridges and many barrels with 7.5twist, 7.3”, and 7”twist from .010” jammed to .100” jump. I have many friends that have done the same. I have thought about getting a 6.75” twist just to succeed, maybe I need to jump even further out. We all report the same info of the flyer in an otherwise solid group. I partially blame it on a mental block. If I were shooting hybrids I would blame myself or a downdraft at distance. However with the 110smk I tend to blame the bullet.
Hey, Donald. We originally planned to include data on the 6mm Sierra 110 Match King bullet, but this week decided to pull it from the article because we only have a small sample size of data for it of 4 tests. But, our original thought was to include it to show an example of a bullet that seems to have very narrow tuning windows, which sounds eerily similar to your experience. So I’ll go ahead and share the data we have, since I already created the visuals and it seems like it’d be helpful for you personally. Just keep in mind it’s a small sample size compared to the data we’ve shared on the other bullets. 
I believe that represents all the data that Mark has confirmed for the Sierra 110 gr. SMK. I know there was a lot of shooters who got excited about it when it was first released, but it seems to have quickly fallen out of favor for many shooters and hasn’t gained a wide following. I have to wonder if this might be at least part of why that is. Again, with a limited set of data on it, I want to be careful to not draw too strong of conclusions. I’m sure Mark might have more thoughts on this that he wants to share too. Thanks,
Cal
I really appreciate both you and Mark sharing this information. It is unfortunate the 110 is so finicky, because the BC is there. My load of 31.5g Varget/450/dasher has been phenomenally consistently in terms of long string ES and SD for every barrel. Which has not made it any easier to give up on it, haha, oh well it’s perfect for fire forming. Honestly it is probably accurate enough for the game. The rest of the data you guys compiled will prove to be invaluable to many shooters. I guarantee you will see a new trend of PRS/NRL shooters that start jumping hybrids in the .065” range.
Thanks, Donald. I am with you. It’s tough to give up on a load when you seem really consistent velocities, but it just isn’t grouping like you want. Like Mark said, there are more than a couple of shooters that seem to have a similar story with the 110 SMK. I’m not sure if it’s the shape of the ogive or what. I’m sure Bryan Litz, Dave Emary, or some the ballisticians at Sierra have an idea what it probably is about the design, but the rest of us just have to learn the hard way! I do think this could be the start of a new trend. At the very least, I hope it makes guys question what might be best for their application and hopefully try it out for themselves to see what works. Thanks,
Cal Thanks,
Cal
Donald, I personally have and I know lots of shooters who have had short “Honeymoon” phases with the 110’s where they are unstoppable one moment, then cannot produce 1 MOA groups. The 110’s seem to have only a .005” window which is around .040” jump. It is a super picky bullet with an extremely small jump window.
Were bullets sorted by ogive?Great article by Mark, You and the contributing shooters. Listened to the Modern Day Sniper Podcast with guest Scott Satterlee just the other day about this subject. It got me to thinking. If you already have your throat cut should you jump a bullet .060″ by seating the bullet deeper? Could it cause a pressure spike? or plan this into your next rifle build with having the freebore cut back more?
Monte MilanukGreat series of articles, guys. I’ve had a few ‘surprises’ over the years that are similar in nature to the “mo jump mo betta” philosophy here, but I’ve never tried taking it anywhere near as far as described in this material. Guess I’ll put that on the ‘to-do’ list to try out soon. Question for Mark (or whomever): have you found the same sort of results on the bigger magnum cartridges? Given the large amounts of powder involved, and the expense of the projectiles, etc. it would be *very* nice to find an approach that reduces the need to ‘chase’ the seating depth on those beasties. Also… does it carry over to solid projectiles?
Thanks, Monte! Honestly, I’d never really tested seating depth much before this. I would seat to what I thought was barely touching the lands or just BARELY off the lands, and do load development for powder charge and go. So this was eye-opening for me too. I’ll chime in with that I’ve heard about magnums, and I’m sure Mark will add his thoughts too. Scott Satterlee believes magnums like to jump even more than what we’re showing here. In the next post, I plan to share some details a friend from Accuracy International told me about after he read my last post. I don’t have all the details ready to share yet, but the summary is after extensive testing on their new Advanced Sniper Rifle in magnum cartridges they also found longer jumps gave better performance. In fact, they specifically said, “The results even surprised me with an increase in accuracy of 19% with the 300 grain bullets jumping about .100″.” That was in the 338 Lapua. Like I said, I’ll mention more about that in the next post, so stay tuned for that. I’m not sure how much of this translates to solids. I’d suspect the testing method could be similar, but I wouldn’t be surprised if the results were different for solids. It seems like they are a completely different animal all together. However, after my post on the “conventional wisdom” when it comes to bullet jumps (meaning jump 0.020″ or less), several people left comments saying that solids typically prefer to jump further. There are several comments in that post talking about it, and you can read those here. Mark, would you mind sharing what you’ve found on bigger magnums? Thanks,
Cal
Great work Cal. Great work. These results are so close to our test results (albeit for copper bullets) that I have a very high level of confidence in your findings. (When you are the only one talking about such things, it’s hard not to feel like John the Baptist preaching in the wilderness – the assumption is always proprietary interest)
Regarding the larger calibres, (and by larger – I mean 375 CT and up) we use a jump of 0.065″ for best results (with our bullets), as opposed to the 0.050″ we recommend for the smaller calibres and cartridges.
You have no idea how much encouragement we take from your latest “findings”. Data beats factoids every day! Love this stuff
Thank you! Steve Hurt
That’s great, Steve! Thanks for chiming in and sharing your findings as well. (For those reading, Steve is from OutrrEdgeProjectiles.com.au) Thanks,
Cal
Wow! My mind is in a pretzel right now from you and the Modern Day Sniper Podcast with Scott’s interview (I need to re-listen after reading your articles) . I have a new barrel being spun up right now, so in 6 weeks, I’m going to be at square 1 trying to find a load. What do you guys recommend I try and start with jump at? Thanks for all that you do
Ha! That’s awesome, Rob. I actually plan to try to summarize how we’d recommend approaching load development in light of all this data in the very next post, so you couldn’t lead into it any better for me! That should be up in less than a week, so you should have it in plenty of time. A lot of it will align with Scott Satterlee, because I’ve had a few conversations with him about all this. So I doubt there will be many surprises for you if you’ve already listened to a podcast about his method. I actually didn’t even know they’d published a podcast on Scott’s approach to load development. I plan to go listen to that right now. For the others that might like to do that, here is a link: Modern Day Sniper Podcast: Scott Satterlee and Hand Loading (Episode 14, Published April 1, 2020) Stay tuned for the next post, Rob! Thanks,
Cal
Rob, I didn’t catch what rifle, cartridge or bullet you’re planning on shooting. We have had an extremely high success rate “spoon feeding” others the correct bullet jump and having them load extremely accurate. But with out knowing what you’re doing, it is hard to help with a recommendation. What you’re going to want to do is start with bullet jump, then move over to charge weight.
Mark, Thanks for commenting back! I’m going to be running a 6.5×47 Remage, 24 inch barrel, 1-8 twist, have a bunch of 140 Hybrids or 130 ELDMs, and H4350 and 4451. I’m thinking I’m going to start with the Hybrids and H4350, but if you have other recommendations, I’m all ears as you’re an expert. Thank you for all you do for the shooting community
Cal,
I think this is one of the best series you have posted, thank you.
I am going to put this info to work on my 7RM.
Best regards,
Phil
Thanks, Phil! I was sure excited about it. It’s why I went dark for a couple of months there. This was a lot to work through, and I wanted to be really careful in how I presented it so that guys could really understand what it’s saying. I’d be embarrassed if anyone knew how much time I spent on this! Mark put a lot of time into it over literally years. But, we’ve both been pleasantly surprised by how well this seems to have been received by the shooting community. This was WAAAAAYYYY off the established path and counter to what many thought of as “best practices” or “conventional wisdom” … so we actually thought there would be a lot of guys pushing back on this or simply dismissing it. Scott Satterlee even told me, “I didn’t want to tell anyone what I was doing, because I didn’t want them to look at me like, ‘What’s wrong with you!'” If you knew Scott, that is a really rare thing for him. I think most of the time Scott couldn’t care less what people think, but this seemed almost like blasphemy in the shooting community. But, like I said … we’ve been pleasantly surprised by the reaction from shooters. At the very least, we were just hoping people would go try it for themselves. Obviously we aren’t trying to sell anything here. In fact, I literally don’t sell anything … all my content is free! Just trying to help out other shooters. So I’m encouraged to hear that is exactly what you’re going to go do: Go give it a shot! Thanks,
Cal
Mark at SAC actually made the rifle that I am shooting now. However it’s a .308 and not a “competition” caliber. Mark mentioned shooting the 178ELDX for hunting with a 0.04-0.06 jump however I decided to shoot the 165 GameKings. I have shot 168 Hornady MATCH out to 1000 yards but seemed to find out that they don’t do too well past 750. (All loads seated 0.020” off the lands) After doing more reading I saw that I needed to go heavier or to the 155 scenars. With my 1/10 twist I decided to go to the 175 SMK. I haven’t been able to do any load development with the 175SMK yet because I just got the bullets and I’m waiting on more powder. Do y’all have any recommendations on where to start or how I can test this?
Galen, We have only did a few tests with the 30 cal. Sierra 175 SMK but have found that the 175 SMK’s like the classis .020″-.030″ jump. So I would give that a shot. By the way, the 175’s touching the lands with the “standard” .070″ freebore reamer is around 2.830″. Putting factory ammo loaded to 2.800″ right at .030″ of jump. I think that is why most rifles love 308 factory ammo with 175 SMK’s.
Dave Beisner Have you done any testing on the .224 Valkyrie ? Any bullet weight ? Dave, We have not had a chance to test much of the .224 cal bullets. David DruckerCal, first I would like to thank you for all the work you put into these posts. I always find them beautifully written and extremely worthwhile! In installment 3 of your bullet jump series, you give velocity data for the first set presented (“test #5 data”) from Mark Gordon’s research. There does not seem to be any correlation between velocity and the Y-coordinate of the shots on target. So, what accounts for the vertical spread at 600 yards? In other words, is there a (lazy?) way to acquire data to determine a forgiving bullet jump at 100 yards, or is it necessary to find a method to identify individual shots on target at 600 yards?
Thanks, David. I appreciate the encouragement and kind words! It’s true that you can’t get everything you need to know about a load by just looking at muzzle velocities. There is not a 1-to-1 correlation with where the bullet hit and muzzle velocity. There is some correlation, but not perfect alignment. While that is sure convenient to only look at muzzle velocity when doing load development, it probably shouldn’t be the only variable you make decisions on. There is an element of raw mechanical precision (i.e. grouping) that involves harmonics, barrel time, and a bunch of things I admit we don’t know a lot about in definitive terms. Now, I’m not talking about group convergence or what some people call positive compensation (i.e. groups being larger at close range and smaller at long range). I think Bryan Litz did a great job exploring that topic in Modern Advancements Vol II. I’m just saying that sometimes you can have extremely consistent velocities and that doesn’t necessarily mean you have small groups. Likewise, you can sometimes have tiny groups, but your velocity extreme spread is ridiculously big. I’ve had experience with exactly that recently. The fact is, muzzle velocities and group size are different variables. Maybe not 100% independent (likely somewhat interdependent), but they are definitely not the same. One can change to a greater or lesser extent relative to the other. However, I’ve spent a lot of time trying to think through how you can try to get the benefit of this kind of testing at shorter ranges, and I’ve talked to several people about it recently too. I hope to provide some tips in the next article, but there is still a little bit of experimentation I hope to do myself this week at the range before I start recommending something to other people. But, I have some ideas … I just haven’t figured out if they are good ideas or bad ones at this point! 😉 Ideally, you’d be able to test all this at distance, but I know that might be impossible for some and really inconvenient for most, so I’m trying to find a way that would give you the most benefit and resolution possible at shorter ranges. I will say I’ve already tried this out a couple times, but I think I have a few refinements to my methods that will help, and I hope to put those to the test this week. I plan to speak to this directly in the next post, which should come out within the next week or so. I just want to try out a few ideas myself before I start suggesting things. Thanks,
Cal
Thanks for your reply! I’ll be looking forward to the next installment. And, for what it’s worth, I am shooting a 6.5 mm Creedmoor using 140 gr Nosler RDFs with a jump of 0.080″.
JOHN GINGRICHVery interesting as usual Cal! I looked at my notes on the DTAC I had commented on the first write up on this that I look for round groups well testing and do 0.030 steps well testing with the dtac 0.060, 0.090, 0.120 had similar results. Thanks again for your time and effort! One thing I should say is this testing was done sub 200 rounds down the pipe 1200 and change later I have not changed my load still going strong (I’m using a 6 slr) I really like you sharing the different methods of finding the lands. That is something I have struggled with over the years as I was looking for the lands to make a mark. 6-8 years ago I spent a couple thousand rounds developing my load testing process using a 223 well running “relatively” 😇 stiff loads I discovered that I have a pressure spike as soon as the bullet started having any marks on them so I deducted that to me the lands start as soon as there is a mark.
I’ve found it interesting or affirming that different things that are coming out with load development I’ve been doing for a number of years and have felt that I’m just not a good enough shooter to see these differences that people talk about over a couple thousandths or a tenth of a grain!!
Has anyone noticed a difference in gun torquing/ twist with different seating depth? Maybe I’m nuts but with heavy bullets I feel the gun torque more with less jump particularly when jamming the bullet.
Thanks, John. This has been really interesting for me to learn about and analyze. I was excited to publish this series, and I know Mark has been as well. It is good to hear that the 115 DTAC data we published here seems to match your own test results. That is a sweet bullet. I ran it in my competition rifle for two years. I recently switched to the 110 A-Tip, but only because I like to tinker and I wanted to play around with those bullets. The 115 DTAC is still a killer bullet, and I think one of the best choices for a 6mm. It is a wind cheater. And it’s funny you say that about measuring the distance to the lands. I had the same experience. I was just using a technique to look for marks on the bullet, but then Mark told me about his method and I’ve been doing that for the past couple of months. I have been SHOCKED by how far off the old method was. It turns out the bullet is in contact with the lands for a considerable distance before it makes marks on the bullets. I have measured the distance to the lands with Mark’s very precise and repeatable method, and compared it to my previous measurements that I’d used for my load development, and it turns out most of my loads were seated into the lands a considerable distance … even those I thought I was off of them. In some cases it was so big that I’m too embarrassed to say how much it was. But, I know now! In fact, to get off the lands I had to seat the bullet in so far that now I’m back within magazine capacity with one of my loads, where I just had to single feed before. So it’s been an eye-opener for me. It does make sense that marks wouldn’t instantly appear when you first make contact, but I just hadn’t ever put much thought into it before this. I do think there will be an endless debate forever about what matters and what doesn’t when it comes to load development. We’ll all fixate on something (me included) as really important, and then we’ll figure out it wasn’t as important as this other aspect, and then we’ll all focus on a different part. We are a funny crowd, and I’m definitely including me in that. I often describe myself as “Strong opinions, loosely held.” If I believe something is true, I usually hold that conviction very strongly … but I’m open and willing to be convinced otherwise. I try to not be overly dogmatic or have a fixed mindset about things that can’t adapt to new information. So some of this is new information is coming out. More people are involved in the sport of precision rifle shooting than any other time in history, so there is a lot of passionate people and new research being done that is furthering our understanding. There are also new products coming out, and people trying to market them and convince all of us we need their new tools … so that is mixed in there. In this case, with bullet jump … we have nothing to sell, but sometimes people are touting new research because it leads you to “need” their product. That is where we all need to be careful. I also think our equipment is now capable of more than it was in the past. Our rifles and the tooling used to build them are 10 times better than 20 years ago! As shooters, we also have access to a lot of training videos and materials that has advanced the entire field of shooters, which wasn’t available to most people just 10 years ago. If you live in Michigan and don’t know one single person who knows anything about long range shooting … if you have an internet connection, you can get into this sport and actually become pretty proficient at it, even in isolation. Because of the huge leap in our equipment and ability, aspects that used to be “in the noise” and “not important” may now become measurable. If you were using an old rifle and you could only group 1.5 MOA and your muzzle velocity had an extreme spread of 50 fps, then using a mandrel to more consistently expand your necks probably isn’t going to produce a measurable difference. But today, you and your rifle might be capable of under 0.5 MOA and if you are careful in other steps of your loading process, then it might make a measurable difference to use a mandrel to expand your necks. So it was true that it “wasn’t important” in the past, but that may not be true anymore. It wasn’t necessarily that we were wrong before, it was just that things have changed since that time … as they always are! But, of course sometimes it was just that we were wrong when we thought it was super-important, or at the very least it wasn’t as important as we once thought it was. I have a friend in the industry who is deep into research and development and his company makes some of the most precise rifles in the world, and he has this quote in his email signature:
“You cannot overestimate the unimportance of practically everything.” – Greg McKeown
That will make you stop and think about it for a second! That quote makes me smile almost every time I see it, because it is just so true! My friend who has that in his signature could be privy to more cutting-edge research than just about anyone in the industry, but I see that quote as him having enough experience to know that we can often get too swept up into a specific thing being critically important. I’ve also heard it said, “If everything is important, nothing is.” If everything has the same level of importance, it is kind of like you saying you don’t know the list of priorities or you can’t provide any direction for what MUST be done. Another good one is, “If everything is life or death, we’ll all be dead a lot.” They all hit around the same idea of how we as humans can over-emphasize the importance of things. Sorry for the book-long response! I just resonate with a lot of your remarks, and it sparked a few thoughts that seemed relevant to this discussion. I don’t have any experience with torquing/twist that you were asking about, but maybe someone else reading this will chime in with their experience. Thanks,
Cal
