what about the chamber causes cases to grow?

[Deleted old_dood]

1/2" up from the head sounds like a case head separation. Was the LC brass new when you started shooting it or was it fired by someone else when you got it. If it was once fired I suspect it was fired in an oversized chamber that allowed the case to stretch badly. If it was new brass it may just be poor brass. I have some LC brass stamped LC72 that I have fired over 20 times and it is fine. .001 to .002 shoulder bump shouldn't cause the case head separations you are having.

LC60. the cases were new. So it's possible MY chamber is oversized. All along, that's been my suspicion. I've got about 150 ready to load. I'm going to start using my old RCBS, non-bushing, neck sizing die an see what happens

old_dood

Is your reply date above a typo, are your cases LC60 or LC06? Cases made at Lake City in 1960 would be during the testing phase of the M16 and the brass was too soft. The specifications for the cases were changed during the jamming controversy and the base of the cases were made much harder.

my mistake. they're actually 09

 

[Deleted old_dood]

Some very good replies and feedback here...but I can't help but wonder why anyone would EXPECT 25 loadings on lc brass in a factory chamber.


My only point is, that many firings from, even very good brass, which lc brass is, is quite good given that the chamber is factory. Custom dies or polishing yours, would likely help your dilemma, if you want to call it one. The fact that you are getting as much stretch as you are says that the brass is being sized too much, somewhere. You have control over how much you bump the shoulders, as you have stated, but diametrically, good die/chamber fit is critical also, to good brass life. That said, I wouldn't expect much more than you are getting from factory dies and chamber...even with proper die adjustment. If you want better, a smaller chamber or bigger die is likely going to be the remedy. Given good brass and pressures, brass life is all about proper die to chamber relationship....JMHO.

in my OP, I never said I expected 25 reloads. I said I was getting failures with less than 10. would you say that would be normal with factory dies/chamber?

 

[bigedp51]

in my OP, I never said I expected 25 reloads. I said I was getting failures with less than 10. would you say that would be normal with factory dies/chamber?

Two pictures are worth 2000 words..........the die below was setup touching the shell holder with the press reaching cam over, the rifle was a new Savage .308.

 

[savagedasher]

I've got two rifles, a Savage LRPV in .223 with original barrel and a Savage 12br in 6mmbr Norma with a Criterion barrel.

I'm using LC brass in the .223 and I trim about .002 off the cases every time I shoot them. I often get cracks around the circumference of these cases with less than 10 firings. The loads are not hot.

On the 6mm I use Lapua brass. I almost never have to trim. Most of this brass has over 25 firings. Out of the original 100 I've had about 4 necks split.

Is this just showing the superiority of Lapua brass or something to do with the rifle's chambers?

I've got a new box of Lapua .223 brass that I haven't used yet and I'm wondering is I should hold off using it until I put a new barrel on the .223. The original barrel has about 2K on it but it shoots and cleans up very well.

The camber design The cases aren't growing the brass is flowing or moving forward while the base isn't . The case has .019 body taper and very little shoulder angle to stop the brass flow. The .002 you trim was from where the case separation is. Po Ackley talks about it in his books. His answer was a straighter case with a stepper shoulder angle. I have both 223 and a 223 AI . 6 loadings on some cases it all I get with the straight 223. 15 loadings and my brass is good on the AI.
New and older reloads try to find Po Ackley volume 1 and 2 their the best books you will ever find on reloading. Larry

 

[Tim Singleton]

I've got two rifles, a Savage LRPV in .223 with original barrel and a Savage 12br in 6mmbr Norma with a Criterion barrel.

I'm using LC brass in the .223 and I trim about .002 off the cases every time I shoot them. I often get cracks around the circumference of these cases with less than 10 firings. The loads are not hot.

On the 6mm I use Lapua brass. I almost never have to trim. Most of this brass has over 25 firings. Out of the original 100 I've had about 4 necks split.

Is this just showing the superiority of Lapua brass or something to do with the rifle's chambers?

I've got a new box of Lapua .223 brass that I haven't used yet and I'm wondering is I should hold off using it until I put a new barrel on the .223. The original barrel has about 2K on it but it shoots and cleans up very well.

The camber design The cases aren't growing the brass is flowing or moving forward while the base isn't . The case has .019 body taper and very little shoulder angle to stop the brass flow. The .002 you trim was from where the case separation is. Po Ackley talks about it in his books. His answer was a straighter case with a stepper shoulder angle. I have both 223 and a 223 AI . 6 loadings on some cases it all I get with the straight 223. 15 loadings and my brass is good on the AI.
New and older reloads try to find Po Ackley volume 1 and 2 their the best books you will ever find on reloading. Larry

This brass flow happens during resizing. If the dies aren't properly set up or are a bad match to the particular chamber

 

[Geno C]

I'll have to say mine grow when firing more than I ever see after resizing. It's the same reason I went with a 243 AI and a 22-250 AI. The little extra speed is nice but it's most for less brass growth for me.

 

[Martin52]

old_dood

As long as you use a mid-range load and the primer is not flush with the bottom of the case the brass will not stretch.

Can you please explain why you say the primer should not be flush with he bottom of the case ?

 

[Baddog0302]

went to the range today with 10 cartridges definitely loaded too hot. 73g boat tails, jammed about .008" into lands, 24g. N140, new Lapua brass. After firing, I saw primers flattened much more that my normal load. When I rechambered these empty cases, I had no resistance closing the bolt. I just neck sized them with an inexpensive RCBS (non-bushing) neck sizing die set so that the necks were sized just short of the neck-shoulder junction. The case lengths were all within .002" of each other. I'm going to reload these exactly the same. Should I just keep doing this until the cases just start having to have some resistance chambering and, at that point, set my FL die bump? At what point can I determine if the chamber is oversized?

That is what I do for my bolt guns. One thing I find that helps is to clean the inside of the case necks, weather the cases are tumble cleaned or not. Then I dip the case necks in a pill bottle full of # 9 shot with HbN added, I feel this eliminates a lot of the drag/pull on the case neck when the expander ball is drug through the neck.
just my $0.02

 

[gunsandgunsmithing]

Some very good replies and feedback here...but I can't help but wonder why anyone would EXPECT 25 loadings on lc brass in a factory chamber.


My only point is, that many firings from, even very good brass, which lc brass is, is quite good given that the chamber is factory. Custom dies or polishing yours, would likely help your dilemma, if you want to call it one. The fact that you are getting as much stretch as you are says that the brass is being sized too much, somewhere. You have control over how much you bump the shoulders, as you have stated, but diametrically, good die/chamber fit is critical also, to good brass life. That said, I wouldn't expect much more than you are getting from factory dies and chamber...even with proper die adjustment. If you want better, a smaller chamber or bigger die is likely going to be the remedy. Given good brass and pressures, brass life is all about proper die to chamber relationship....JMHO.

in my OP, I never said I expected 25 reloads. I said I was getting failures with less than 10. would you say that would be normal with factory dies/chamber?

Ok...I took it as you were asking why you aren't able to get 25 firings with this gun and brass like you are getting with the other gun and brass. Everything I said is still true.

 

[BoydAllen]

For once fired brass, I set my FL dies so that the shoulder location is the same as it came out of the chamber after firing, and then check the first case in the rifle to see if there is a bolt close issue. Every time that I have done this, there has not been. This is because it takes more than one neck sized firing for a case to reach its maximum "headspace". It is this maximum that I use for a reference when setting shoulder bump. When I first get a rifle, or new barrel, I load and fire a case until it reaches its maximum dimension, set it aside, and use it for a reference.

As a case is fired, first the force of the firing pin, and the primer knock it forward in the chamber. Cases that have smaller shoulder angles are generally driven farther forward as this happens. This increases stretch at the back of the case, especially if the chamber finish is on the coarse side. As the pressure of the burning powder rises, the sides of the case cling to the chamber, and the back of the case is stretched when the pressure gets to the point that the head of the case is pushed back to the bolt face. This thins the brass a little way in front of the solid head, and will cause a bright line, and then a crack. If you modify your reloading procedure so that there is only enough clearance at the head and shoulder so that the bolt can be operated with only slight feel, then you will have fewer of these types of failures.

Back in the day, when I was loading for a Savage .220 Swift (as case with a relatively small shoulder angle, and quite a bit of body taper) I found that if I bumped once fired brass at all, that I got a bright line on the next firing. Setting the die so that a once fired case was not bumped at all solved the problem. By bumping the cases, I had let it have "a run at" the front of the chamber, which allowed it to be driven farther forward during firing, causing excessive stretching at the back of the cases, and the bright line, that was a symptom of thinning that would have eventually lead to a separation. Your 6BR has a sharper shoulder, and less body taper, and is therefore much less prone to being driven forward during firing.