Bullets Taking a Set

F

Fla mac

Guest
All,
I had something happen the other day that got me thinking. I had loaded some 30BR rounds to do some load testing and find that the OAL was too long and that they needed to be reseated. I set my die to the right length and start reseating my rounds. When I would reseat each round it would take more force to break the bullet than it did when I first seated them. Has anyone experience this. The rounds had been loaded for about 3 or 4 days. If you let your rounds sit for 3 or 4 days does the bullet take a seat? Will this effect neck tension if you jam into the lands?
john
Mims, Fl.
 
Erratic OAL in the 30BR usually is caused by a high powder column compressed by the bullet base. I load 34.5 grs. H4831, and if the OAL is measured days later, it is usually higher than when fresh loaded. Some shooters believe the brass takes a set if not shot immediately, but usually the difference is felt in less seating tension.
 
John ...

Fla mac said:
All, I had something happen the other day that got me thinking. I had loaded some 30BR rounds to do some load testing and find that the OAL was too long and that they needed to be reseated. I set my die to the right length and start reseating my rounds. When I would reseat each round it would take more force to break the bullet than it did when I first seated them. Has anyone experience this. The rounds had been loaded for about 3 or 4 days. If you let your rounds sit for 3 or 4 days does the bullet take a seat? Will this effect neck tension if you jam into the lands? john Mims, Fl.
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RELOADING TIP--Neck Tension vs. Time

We've learned that time (between neck-sizing operation and bullet seating) can have dramatic effects on neck tension. Controlling neck tension on your cases is a very, very important element of precision reloading. When neck tension is very uniform across all your brass, you'll see dramatic improvements in ES and SD, and your groups will shrink. Typically you'll also see fewer fliers. Right now, most reloaders attempt to control neck tension by using different sized neck bushings. This does, indeed, affect how hard the neck grips your bullets. However, James Phillips recently discovered that another critical factor is at work. He loaded two sets of 22 Dasher brass. Each had been sized with the SAME bushing, however the first group was sized two weeks before loading, whereas the second group was neck-sized just the day before. James noticed immediately that the bullet seating effort was not the same for both sets of cases--not even close. Using a K&M Arbor press equipped with the optional Bullet-Seating Force Gauge, James determined that over twice as much force was required to seat the bullets which had been neck-sized two weeks before. The dial read-out of seating force for the "older" cases was in the 60s, while the seating force for the recently-neck-sized cases was in the 20s. (These numbers correspond to pounds of force applied to the bullet). Conclusion? In the two weeks that had elapsed since neck-sizing, the necks continued to spring back (get tighter) and stiffen. Lesson learned: for match rounds, size ALL your cases at the same time. If you want to reduce neck tension, load immediately after sizing.

Source: http://bulletin.accurateshooter.com/ :)
 
The high load required to move a bullet in the case is simply due to the difference between static and dynamic friction. When the bullet was seated in the case during reloading you were moving the bullet into place so it was dynamic or sliding friction you were working against. When you try to break it free you are then dealing with static friction which is always higher. This higher load required to break the bullet free is not due to any chemical or corrosive action.

The true load or stress that exists between metals in contact is often not recognized. Its actually equal to the yield strength which in the case of copper or brass is on the order of 10,000 - 50,000 psi. So it's this kind of true pressure at many very small points of contact that you have to work against to move the bullet in the case. Under very high loads there is also a certain amount of creep taking place which is a process where time enters in, thus the differences that are noted when some time has passed.
 
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abintx said:
In the two weeks that had elapsed since neck-sizing, the necks continued to spring back (get tighter) and stiffen.
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I can handle that brass might try to assume an earlier state over time, but when we size with a bushing or collet die, shouldn't we expect the brass to assume a larger diameter?
 
Pacecil! You're still with us!

pacecil said:
The high load required to move a bullet in the case is simply due to the difference between static and dynamic friction. When the bullet was seated in the case during reloading you were moving the bullet into place so it was dynamic or sliding friction you were working against. When you try to break it free you are then dealing with static friction which is always higher. This higher load required to break the bullet free is not due to any chemical or corrosive action.

The true load or stress that exists between metals in contact is often not recognized. Its actually equal to the yield strength which in the case of copper or brass is on the order of 10,000 - 50,000 psi. So it's this kind of true pressure at many very small points of contact that you have to work against to move the bullet in the case. Under very high loads there is also a certain amount of creep taking place which is a process where time enters in, thus the differences that are noted when some time has passed.
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Pacecil, I haven't seen any posts by you lately. I was afraid some of my smart a$$ remarks might have run you off, and I wouldn't want that. :) I'm serious.

You're one smart cookie and I'm not being facetious when I say that. I still wish I knew who you are. Whoever you are you're certainly a pro at what you do. Thanks for sharing your expertise here on the forum with rednecks like me. :)

Gene Beggs
 
John Kielly said:
I can handle that brass might try to assume an earlier state over time, but when we size with a bushing or collet die, shouldn't we expect the brass to assume a larger diameter?
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John, that was my impression of what would happen, that in "relaxing" after sizing the necks would become larger rather than smaller. Strangely I've noticed that bullets that seat very easily can be very hard to pull. I shoot only moly coated bullets too.
 
pacecil said:
The high load required to move a bullet in the case is simply due to the difference between static and dynamic friction. When the bullet was seated in the case during reloading you were moving the bullet into place so it was dynamic or sliding friction you were working against. When you try to break it free you are then dealing with static friction which is always higher. This higher load required to break the bullet free is not due to any chemical or corrosive action.

The true load or stress that exists between metals in contact is often not recognized. Its actually equal to the yield strength which in the case of copper or brass is on the order of 10,000 - 50,000 psi. So it's this kind of true pressure at many very small points of contact that you have to work against to move the bullet in the case. Under very high loads there is also a certain amount of creep taking place which is a process where time enters in, thus the differences that are noted when some time has passed.
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I recently loaded about 65rds using a loose seater stem (duhh)

I went back and reset them all DOWN (luckily) from about .002 to about .010. Not only were they hard to start, they varied considerably in force required.

al
 
We have discussed this before, but how many times have you shot some loaded rounds left over from a match a couple of weeks before, and have them all go in the same hole. One of those strange phenominas. It makes me want to pre-load 200 rounds for the up comming Unlimited Nationals and let them "age" a while...........jackie
 
This is another one of those instances where if you do a little of the math you will find that the bullet is only under the influence of neck tension for just a few thousandths of it's travel in the neck. Once the neck expands due to internal gas pressure, and the bullet has moved a little, the bullet will be "floating free". What this means is that normal neck tension, or friction of neck tension, has little effect on gas pressure or bullet velocity, and thus little effect on where the bullet hits the target.

It should be pointed out though, very high tension such as caused by a crimp or low neck clearance would allow the pressure to rise in the case before the bullet has broken free. This probably will affect bullet poi.
 
pacecil,
With all due respect to applied mathematics, sometimes although the calculations may be done correctly, there may be more happening than the engineer has imagined. If what others are reporting was merely the difference between static and dynamic friction, wouldn't this be seen when seating in two steps, as in when one seats part way, rotates the cartridge and then finishes? Do the stress strain curve, and yield points of brass change with work hardening? The reason that I ask is that I have seen considerable difference in the annealing of new brass, even from a high quality brand like Lapua. We ran into this when Fl sizing once fired .338 Lapua brass, as excessive variance in shoulder bump at the same die setting. Doing less than a full anneal of the neck shoulder area, with a machine, solved the problem. The reason for the question about physical properties as related to work hardening is that one of the results of working brass would seem to be disturbance of grain boundries, which may re-consolidate over time, sort of like disturbed earth. This is just a theory, but it might explain the experiences that many of us have had that abintx referred to.
 
To Boyd Allen

The difference you would expect to see if you stopped and started the seating operation is going to be very slight. The force needed to seat bullets is low to begin with so it is difficult to see the difference between static and moving forces. However when I seat bullets I can detect the difference in my press.

As to the effect of changes in the brass properties being the reason for higher load to unseat a bullet after it has been seated for some time - this would be possible but not for the reasons you think. Annealing or work hardening brass changes only it's strength not it's modulus of elasticity or stress/strain curve.. As I pointed out in a previous post there could be "creep" take place (on a micro scale) in the brass or copper between the surfaces that causes the two surfaces to "mate" or "fit" together better. Who knows, this may be partly the reason behind the difference in static and dynamic friction between all materials. This type of change is really a change to surface geometry rather than a change in the properties of the brass or copper.
 
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The one problem that I see with the creep theory is that it does not explain the radical (more than can be explained by a reduction in ID) change in seating force required for brass that has been aged between sizing and seating. I do believe in some sort of creep, because I have found that the fit of case necks on turning mandrels changes, with time, after expanding. I guess my grain boundary theory would explain both the creep and the difference in elasticity.
 
All,
I would love to do some work on bullet seating and pulling test with a UTM (Tinius Olsen Pull Test). We did bullet pull test on the Smaw spotting rounds when I worked at MDAC. We found that it would take more force to start the bullet moving than it did to keep it moving. The round was a 9mm jacketed bullet with a tracer that could only be seen from the back. The case was a 308Win. with a 22 hornet blank inside the 308 case. The copper jacket did not go the full length of the bullet, so you had copper and lead in the neck of the 308 case. We had data all other the place, so we just used the bullet hits on the target to qualify the round. I was thinking like you Jackie load enough to shot a match about a week before and let them age. When I go to a match I like to shot about 25 rounds the day before the match and reload them that night, but I think I will stop doing that, or just use the reload rounds to foul the barrel.
John
Mims, Fl
 
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