Bullet Jump/Jammed - Is it the Bullet design or the rifle

asd9055

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Have you contacted one of the Master bullet smiths from a manufacturer? They might have the answer for you.
That's a good idea, Berger might be a prime candidate since they actually have a recommended procedure. I will think about that
 

Mikecr

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Bullet seating is no more tuning than primer swapping is.
Both are prerequisite to best tune,, they can both take you out of tune, but you cannot actually tune with either.
You tune with powder(right to the kernel) and neck tension.

Full seating testing, as Berger recommends, is a coarse process to find the land relationship that a bullet likes in YOUR barrel. This cannot be predicted but has to be tested for. JUST LIKE PRIMER SWAPPING.
Both cause huge dispersion changes, way beyond that of actual tuning with powder.
With full seating testing, you can make a 1/4moa gun open to 3/4moa & back. No amount of powder change(type or amount) can do that, and you will not recover from worst seating or worst primers -with tuning.
That's why it's vital, right up front, to determine best bullet seating, and best primer, as prerequisites to tuning.
Also, once you have determined best seating with a bullet/barrel, and best primer for powder/cartridge, this does not change. Even if you start load development over with a different powder, best seating remains just the same.
It is independent of tune.

If ~50yrs ago they knew just this much about it, then by now we would have our chambers cut to standards for particular bullets, and we could look up on a table exactly where best seating is.
You know what progress we've made in this regard, for ~100yrs? NONE
You can go ahead and ask bullet makers for reamer prints and seating tables for their bullets. If they even attempt to skirt around that with folklore & BS, at least know it for what it is: They know no more than you do.
So your endeavor to understand this is great, but you won't learn anything by asking around.
It's just the way it is with small arms and humans in general.
 

asd9055

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Joined
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Messages
361
Location
Texas
Bullet seating is no more tuning than primer swapping is.
Both are prerequisite to best tune,, they can both take you out of tune, but you cannot actually tune with either.
You tune with powder(right to the kernel) and neck tension.

Full seating testing, as Berger recommends, is a coarse process to find the land relationship that a bullet likes in YOUR barrel. This cannot be predicted but has to be tested for. JUST LIKE PRIMER SWAPPING.
Both cause huge dispersion changes, way beyond that of actual tuning with powder.
With full seating testing, you can make a 1/4moa gun open to 3/4moa & back. No amount of powder change(type or amount) can do that, and you will not recover from worst seating or worst primers -with tuning.
That's why it's vital, right up front, to determine best bullet seating, and best primer, as prerequisites to tuning.
Also, once you have determined best seating with a bullet/barrel, and best primer for powder/cartridge, this does not change. Even if you start load development over with a different powder, best seating remains just the same.
It is independent of tune.

If ~50yrs ago they knew just this much about it, then by now we would have our chambers cut to standards for particular bullets, and we could look up on a table exactly where best seating is.
You know what progress we've made in this regard, for ~100yrs? NONE
So your endeavor to understand this is great, but you won't learn anything by asking around. It's just the way it is with small arms and humans in general.
Thanks Mike, I appreciate your thoughtful reply. Never hurts to ask, right?
 

Mikecr

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It's great to see someone head for understanding -instead of merely what people do or think they're doing.
For every direction to look, be sure to consider other tests passing/failing.
Only truths pass ALL tests.
 

asd9055

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misterc01

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That's a good idea, Berger might be a prime candidate since they actually have a recommended procedure. I will think about that
I got a LOT of information from them on bullet seating and lot more. Not to step on toes, but experts such as Erik Cortina seem to indicate that getting the seating depth for the best accuracy is part of the tuning process for the best accuracy along with powder variations, primer swapping, neck tension, and whatever.
 

asd9055

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I got a LOT of information from them on bullet seating and lot more. Not to step on toes, but experts such as Erik Cortina seem to indicate that getting the seating depth for the best accuracy is part of the tuning process for the best accuracy along with powder variations, primer swapping, neck tension, and whatever.
I am not questioning it, I am trying to understand the what/why
 

Bruce Treloar

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It's not rocket science so I'll keep it simple. All chambers vary re lead into the lands, slow powders usually shoot better well off the lands . Fast powders are usually better on or just off, however there are exceptions so start about 10-25 thou off then try by increasing the jump 10 thou at a time. I wouldn't think going more than 60 thou is necessary. You will be able to tell from the horizontal or vertical group which way to go in or out. One rifle I had used to shoot 1/4' 15 though off and after rebarreling it needed to be 55 thou off the lands to produce that sort of accuracy.
 

asd9055

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It's not rocket science so I'll keep it simple. All chambers vary re lead into the lands, slow powders usually shoot better well off the lands . Fast powders are usually better on or just off, however there are exceptions so start about 10-25 thou off then try by increasing the jump 10 thou at a time. I wouldn't think going more than 60 thou is necessary. You will be able to tell from the horizontal or vertical group which way to go in or out. One rifle I had used to shoot 1/4' 15 though off and after rebarreling it needed to be 55 thou off the lands to produce that sort of accuracy.
I am not looking for anyone to teach me how to figure out what the what the "bullet jump" should be in my rifle. You are right, its not rocket science, just read the question and if you can not answer it, don't!
Thank you!
Actually it has a lot to do with rocket science...just don't know how to figure out the equations!!!!
 

jeffwhitcomb

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With the knowledge of this group, I think the reason that you haven't gotten an answer to your question is because I don't think it really can be answered by an equation. The variables that would need to be measured and inputted into an equation would be almost impossible. For example, two identical barrels (what we would call identical) are built and chambered. The steel will have its own imperfections at different locations, the rifling process is impossible to perfectly duplicate, the chamber reamer will have different amounts of wear and lathe setup will all have an effect on how a barrel responds harmonically and how seating depth will effect accuracy. It was suggested before to speak to the bullet manufacturers and I believe that would be a great resource to understand a little more about why certain bullet designs are more forgiving in terms of seating depth, but all other factors (mostly human and tool wear) nearly prohibit a mathematical solution to what seating depth is the best and why it is.
 

Dragoon300

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I think the answer to your question is simpler than we want it to be. I am a machine design engineer by trade, and live in the precision machining world. I also enjoy shooting, and even more tinkering with my guns. In my experience with my primary precision rifle, a Desert Tech SRS 338 Lapua, I wanted to utilize all of the case capacity while using Berger 300 grain OTM bullets. I wanted to seat the bullet so the boat tail shank junction was at the case neck shoulder junction giving me the most capacity and the full neck for retention and bearing surface. Then I throated the chamber to give me .010" off the rifling so as to not jam the bullet into the rifling because I need to be able to unload without leaving the bullet in the chamber, simple as that. The OTM Hybrids are supposed to be "more tolerant" to jump and I must say that is true in my case, I did not see any real difference initially in testing, and now after 800 plus rounds with the throat eroded .020" more the accuracy is still 1/4 MOA. Mechanically the design shape of the bullet and the lead into the rifling are what make jump more or less tolerable. The benchrest guy's jam their bullets into the rifling because it is more accurate, as the bullet is started into the rifling before ignition. Practical shooters can't do this because they could induce a problem no one wants during unloading, so they must stay back some amount. Manufacturers design more throat into a rifle cartridge to allow for a greater range of bullets, but I believe mostly to reduce pressure as in Weatherby magnums and Remington ultra magnums where they have .300" to .400" to be safe. If you take a .300 ultra mag and load it with a 110 grain bullet it will space walk before entering the rifling. This is the other end of the spectrum from the benchrest guy's! So, I can only say what I know to be true in my case, I had lots of bearing contact in the case neck and only .010" to the rifling (when new) and this helps. I just had Dave Manson make a reamer to my specifications for my Lapua, and one for a 6.5 PRC with Berger 156 grain EOL's and plan on doing the same. I will see how it works out, but am quite sure it will with .010" jump and tuning my load to suit. Hope I didn't get too long winded and this helps.
 

asd9055

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Messages
361
Location
Texas
With the knowledge of this group, I think the reason that you haven't gotten an answer to your question is because I don't think it really can be answered by an equation. The variables that would need to be measured and inputted into an equation would be almost impossible. For example, two identical barrels (what we would call identical) are built and chambered. The steel will have its own imperfections at different locations, the rifling process is impossible to perfectly duplicate, the chamber reamer will have different amounts of wear and lathe setup will all have an effect on how a barrel responds harmonically and how seating depth will effect accuracy. It was suggested before to speak to the bullet manufacturers and I believe that would be a great resource to understand a little more about why certain bullet designs are more forgiving in terms of seating depth, but all other factors (mostly human and tool wear) nearly prohibit a mathematical solution to what seating depth is the best and why it is.
Jeff
I appreciate your thoughts. I was not expecting equations, its just that some people don't read the questions, and start typing. When something works, I accept it, and I use it, but then I want to understand the how/what/why. I read the same articles some people suggested, I even posted them here in other threads.
I started thinking about this because I have three rifles, one built in 1959, one in the mid 1980's and one around 2008 in three different countries. One has even a different barrel contour. Common thing is Brand and caliber. Yet they all shoot the same with the same bullet and load. So I started thinking. Is it the bullet, to rifle as a system, the chamber/throat or the caliber that is the biggest factor in bullet jump. I was looking to see if anyone has experimented or had any experience. I have learned a lot from the members of LRH and other forums.
Yes, the suggestion to reach out to bullet manufacturers was probable the best and I plan to reach out to Berger. To my knowledge they are the ones that talk about bullet jump.
Again thanks.
 

asd9055

Well-Known Member
Joined
Nov 15, 2013
Messages
361
Location
Texas
I think the answer to your question is simpler than we want it to be. I am a machine design engineer by trade, and live in the precision machining world. I also enjoy shooting, and even more tinkering with my guns. In my experience with my primary precision rifle, a Desert Tech SRS 338 Lapua, I wanted to utilize all of the case capacity while using Berger 300 grain OTM bullets. I wanted to seat the bullet so the boat tail shank junction was at the case neck shoulder junction giving me the most capacity and the full neck for retention and bearing surface. Then I throated the chamber to give me .010" off the rifling so as to not jam the bullet into the rifling because I need to be able to unload without leaving the bullet in the chamber, simple as that. The OTM Hybrids are supposed to be "more tolerant" to jump and I must say that is true in my case, I did not see any real difference initially in testing, and now after 800 plus rounds with the throat eroded .020" more the accuracy is still 1/4 MOA. Mechanically the design shape of the bullet and the lead into the rifling are what make jump more or less tolerable. The benchrest guy's jam their bullets into the rifling because it is more accurate, as the bullet is started into the rifling before ignition. Practical shooters can't do this because they could induce a problem no one wants during unloading, so they must stay back some amount. Manufacturers design more throat into a rifle cartridge to allow for a greater range of bullets, but I believe mostly to reduce pressure as in Weatherby magnums and Remington ultra magnums where they have .300" to .400" to be safe. If you take a .300 ultra mag and load it with a 110 grain bullet it will space walk before entering the rifling. This is the other end of the spectrum from the benchrest guy's! So, I can only say what I know to be true in my case, I had lots of bearing contact in the case neck and only .010" to the rifling (when new) and this helps. I just had Dave Manson make a reamer to my specifications for my Lapua, and one for a 6.5 PRC with Berger 156 grain EOL's and plan on doing the same. I will see how it works out, but am quite sure it will with .010" jump and tuning my load to suit. Hope I didn't get too long winded and this helps.
Dragoon,
Thank you for taking the time for a thoughtful response. I am an engineer as well, and I don't have to run my own experiment to accept the results, however I usually try to understand why.
So in your experience, if you were to shoot a different 300 grn bullets, one that is of tangent design and one that is of secant design, would the 0.010" of the lands shoot the same?
I believe in the articles on bullet jump, Mark suggests looking for the most "forgiving" bullet jump to allow for throat erosion down the road. For the OTM in your case it might be 0.010" of the lands which would mean bullet design might be the biggest factor. That is what I am trying to determine. I don't have the answers, was looking for people who tried different bullets in the same rifle and see what they experience
Again, thank you
 

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