what about the chamber causes cases to grow?

[Deleted old_dood]

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.

 

[Tim Singleton]

Your chamber isn't the problem IMO
You are over sizing your 223 brass. The brass grows when sized the die squeezes it back into shape the material has to go somewhere. If your brass has to be trimmed that much after each sizing you are sizing to much for that chamber. Is the crack you mention at the base of the brass? If so this is case head seperation and is a clear sign of over sizing

 

[jlow]

A couple of things, one is cracks around the circumference (I imagine you mean the case mouth) is due to work hardening. I imagine your trimming might work hardened them apart from other sizing work – do you anneal? That would soften the metal out and prevent cracking.

Lapua brass I generally like but one thing that has puzzeled and troubled me is they appear to come short. For example, SAAMI spec for 223 is 1.7598 but my last batch of 27 new cases I measured range between 1.7520 to 1.74850 with an average of 1.74985. It of course means I don’t have to trim for a few go around but I guess I would like to have them a little longer so that less of the chamber would be exposed and also I could trim them to a consistent length without having to go down too low. Would be interested in what others think?

 

[Deleted old_dood]

Your chamber isn't the problem IMO
You are over sizing your 223 brass. The brass grows when sized the die squeezes it back into shape the material has to go somewhere. If your brass has to be trimmed that much after each sizing you are sizing to much for that chamber. Is the crack you mention at the base of the brass? If so this is case head seperation and is a clear sign of over sizing

I use the Hornady headspace gauges. I'm bumping the shoulder back minimally, .001 to .002. The die is Redding Type S, Forster Coax press. The press doesn't even cam over in order to get the amount of bump I'm getting.

Should I not bump at all until I get resistance chambering and then start bumping?

The cracks occur about 1/2" up from the head.

 

[coford]

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.

 

[Tim Singleton]

I found out through a similar experience as you describe that going by shoulder bump isn't the only thing to check when determining the amount your die is sizing the case. Take a set of dial calipers and a fired case lock the calipers down at the case shoulder junction. Size the case with your current set up then slide the calipers down the body of the sized case. Tell us how far they go down the case.
Research case head separation

 

[bigedp51]

old_dood

Was your Lake City brass once fired brass or was it fired only fired in your rifle?

If you have once fired brass it could have been fired in a machine gun that has a chamber .003 to .004 larger in diameter than commercial SAAMI standards and much longer headspace settings. Meaning it may have stretched a good deal in diameter and length when fired.

If your brass was new Federal ammunition with Lake City head stamps this brass did not pass quality control standards at Lake City Army Ammunition Plant and rejected by the military.This brass that failed inspection is then loaded by Federal in Minnesota, this brass is NOT unsafe to fire "ONCE" BUT it was rejected for a reason by the military.

If you didn't remove the primer pocket crimp, then the brass wasn't once fired no matter what was said when you bought the brass.

If you go to AR15 forums and read the posts by the people running AR15 shooting camps you will see there are some brands of cartridges they do not like and one of them is Federal made 5.56 ammunition with Lake City head stamps. Bad ammunition slows down the training with stoppages and many of these training camps will not let the students use curtain brands of ammo.

If it isn't the Lake City cartridge cases the only thing left is your chamber or your dies.

 

[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

 

[jlow]

Case head separation is caused by oversizing or oversized chamber. Since you are only bumping down 1 to 2 thousands then it is your chamber. Measure the headspace of a fired brass and compared it to SAAMI standard and/or a new piece of brass and you will have your answer.

 

[243winxb]

Re: what about the 223 chamber causes cases to grow?

Should I not bump at all until I get resistance chambering and then start bumping?

Yes, but keep in mind, the firing pin strike may set the shoulder back .006" Full pressure loads are needed to fully expand the brass to the chamber again.

 

[searcher]

As JLOW said, you need a "REFERENCE CASE" to use to set up your die properly. You may have used a case previously fired in your chamber, but that shoulder may not have been fully blown forward, thus giving you a bad reading when you measured it to set up your dies. Best to Jamb a bullet into the lands with a lighter load, thus you may get your shoulder blown to where it needs to be for an accurate measurement for die set-up.

Lake City brass will eventually get cracked necks sooner that lapua. Unlike Lapua (usually), it must be annealed to prevent this from happening. I do mine every 6 loadings or so and no problems after that. Of course, you can extend the life of Lapau by periodic annealing also.

You don't state whether your "s" bushing dies are full-length sizing dies or just neck dies. If they are full-length sizing dies - that explains a lot of the work hardening, especially if you still have the ball expander in the die.

I too believe you are over bumping the shoulders. ONCE you have a good case that the shoulder has been fully blown forward, use it to set up you bump to be no more than .001". You may wish to experiment with no bump till needed - or just go for less than .001". The more bump - the more you will see brass flow and trim.

If the cracks appearing are around the circumference of the base of the caee, say about 1/2" from the bottom, I'd discard all cases in that batch and start anew with fresh cases. The cases have just been overworked (and maybe some hot loads also?) and case seperations will likely continue to occur.

Lake City is great brass but is not on par with Lapua for longevity.

 

[Deleted old_dood]

As JLOW said, you need a "REFERENCE CASE" to use to set up your die properly. You may have used a case previously fired in your chamber, but that shoulder may not have been fully blown forward, thus giving you a bad reading when you measured it to set up your dies. Best to Jamb a bullet into the lands with a lighter load, thus you may get your shoulder blown to where it needs to be for an accurate measurement for die set-up.

Lake City brass will eventually get cracked necks sooner that lapua. Unlike Lapua (usually), it must be annealed to prevent this from happening. I do mine every 6 loadings or so and no problems after that. Of course, you can extend the life of Lapau by periodic annealing also.

You don't state whether your "s" bushing dies are full-length sizing dies or just neck dies. If they are full-length sizing dies - that explains a lot of the work hardening, especially if you still have the ball expander in the die.

I too believe you are over bumping the shoulders. ONCE you have a good case that the shoulder has been fully blown forward, use it to set up you bump to be no more than .001". You may wish to experiment with no bump till needed - or just go for less than .001". The more bump - the more you will see brass flow and trim.

If the cracks appearing are around the circumference of the base of the caee, say about 1/2" from the bottom, I'd discard all cases in that batch and start anew with fresh cases. The cases have just been overworked (and maybe some hot loads also?) and case seperations will likely continue to occur.

Lake City is great brass but is not on par with Lapua for longevity.

what I'm going to do is just neck size until there's some resistance chambering. I'll also try some hot loads like you suggested.

 

[jlow]

That may or may not help you.

If your problem is oversizing then yes it will help. However, If you chamber is in fact oversized, then the very first time you fire a hot load the case will be over stretched to full chamber dimension. Since cases do not stretch evenly when that happens but usually at that point ½” from the bottom, you have already damaged your case irreversibly and it is just a matter of time before you get a case head separation.

 

[Deleted old_dood]

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?

 

[bigedp51]

old_dood

I collected milsurp rifles and all the chambers were over-sized by SAAMI standards, meaning larger in diameter and longer in headspace settings. In order to shoot some of these older milsurp rifles you just neck sized and occasionally bumped the shoulder back to allow the case to chamber freely.

If you look below at this SAAMI case and chamber drawing you will see that the distance between minimum and maximum headspace is .010. I have had old milsurp rifles that were over this .010 headspace limit and the fix was simple, "DO NOT OVER RESIZE" the brass meaning keep the shoulder bump to a minimum amount. Another way to look at it is the chamber isn't too long, the brass is just too short, and you are fire forming the brass to fit your chamber.

The worst rifle I have ever seen with the greatest differences between the American SAAMI standards and military standards was the British .303. And at maximum military headspace you could have .017 head clearance with commercial cases, with its long and fat military chamber. On top of this emergency war time headspace was .010 over normal maximum headspace settings or .020 between minimum and maximum.

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. What I'm getting at is sometimes "normal" methods for fire forming cases are very hard to do and if you fire the case with the above mid range and then full length resizing you can make the case "LONGER".

If you fire your cases with a mid-range load and when resizing them and have approximately a .010 gap between the shell holder and the die your brass will grow in length.

Look at the illustration below and pay attention to the blue, red and green dotted lines and the words "shoulder setback" you will understand what I'm saying.

On some of my old WWI and WWII Enfield rifles to fire form the cases a rubber o-ring was slipped over the case to hold the case against the bolt face to prevent case stretching in the web of the case.

You can jam the bullets into the lands as a fire forming method at reduced loadings or create a false shoulder on your cases and fire form. So again, the chamber is seldom too long the brass is just too short with considerations for the cartridge type and chamber pressure.

Then again if your headspace is 1/2 to 3/4 of an inch over maximum headspace you have to worry about the front of the case being sucked into a black hole and seeing the blue red light shift as the neck of the case reaches light speed.

 

[Tim Singleton]

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?

Most people do just as you describe if they run into a fat chamber. Neck size only and you can probably load many times before they feel tight when the bolt closes. The thing is to set up your full length die to size the very minimum amount when you do use it. Measure a brass that has not been fired in your gun at just above the extractor groove. Record this measurement. Compare to several you have fired and neck sized only. Then when you do full length size set the die so as not to size the base of the brass to much. See how they feel going into the chamber. Some dies set to bump the shoulder .001-.002 actually size the base a lot more than you know if you aren't measuring it this is the problem area over sizing the brass at the head

 

[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.

 

[243winxb]

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?

Neck sizing till the rounds are hard to chamber works for me. But if you think there may be a chamber problem, i would buy a Headspace Gage, Field Length, to check it. Field Gage: Field Gages correspond to the maximum safe headspace dimension. If a rifle will chamber a field gage, it should be inspected and repaired by a competent gunsmith prior to use. http://www.midwayusa.com/product/383456/forster-headspace-gage-field-length-223-remington What is the loading your using? High pressure may make the trim length grow from what i read. I know you said loads are "not hot"

 

[bigedp51]

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.

 

[Deleted old_dood]

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?

Neck sizing till the rounds are hard to chamber works for me. But if you think there may be a chamber problem, i would buy a Headspace Gage, Field Length, to check it. Field Gage: Field Gages correspond to the maximum safe headspace dimension. If a rifle will chamber a field gage, it should be inspected and repaired by a competent gunsmith prior to use. http://www.midwayusa.com/product/383456/forster-headspace-gage-field-length-223-remington What is the loading your using? High pressure may make the trim length grow from what i read. I know you said loads are "not hot"

I checked with PTG GO and NOGO gauges.