Looking for some insight on this one as I’m stumped. I’m working up a load for a new 308 and I had some confusing results. Reloading 1x fired brass, checking all the typical measurements, take em out to the range and fire away. Now the interesting part, I’m showing pressure signs on fairly low charge weights with varget seated 10 thou off the lands (42.5gr and up) and the brass growth at the shoulder is avg 20 thou growth. I’ve checked the rifles headspace with gauges. Checked this with factory ammo as well and same result. I’m not new to reloading and my process is very meticulous so I don’t really know where to go with this one. Any ideas?
Strange 308 issue.
- Thread starter gcoy19
- Start date
0.020" growth at the shoulder?? That is a lot, IMO. I take it you mean that the dimension from the case head to the 0.400" datum on the shoulder increased by 0.020"? This is a bolt gun? If the headspace gauges are correct, I don't understand how a round can grow that much unless something is shifting when the rifle fires.
Did this happen under wet conditions?
Any chance there's an oil film on the chamber walls?
Did this happen under wet conditions?
Any chance there's an oil film on the chamber walls?
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If your brass is "growing" or the shoulder is being pushed forward .020" when fired, the bolt would close on the "Go" Gauge and you would have too much headspace. The bolt should just close without force on the "Go" gauge. If you put a piece of scotch tape on the back of the go gauge the bolt should not close.
Mystic Precision
CGN Ultra frequent flyer
- Location
- Summerland, BC
Can you please confirm the dimensions again...
Headspace of the rifle chamber is within spec - confirmed with headspace gauges.
AFTER firing the brass gets 20 thou LONGER? Shoulder is moving forward vs after sizing in your die?
Or do you mean, the DIAMETER of the case shoulder is WIDER by 20 thou... the headspace stays within expectations?
"Growth" is unclear so please indicate WHERE the dimension is changing. It is alot but one option can be just not desireable but not dangerous... the other can be super dangerous.
If you need to post pics so you can mark/point where you see this grow and when...
I have a few ideas but lets clarify what you actually mean.
Jerry
Headspace of the rifle chamber is within spec - confirmed with headspace gauges.
AFTER firing the brass gets 20 thou LONGER? Shoulder is moving forward vs after sizing in your die?
Or do you mean, the DIAMETER of the case shoulder is WIDER by 20 thou... the headspace stays within expectations?
"Growth" is unclear so please indicate WHERE the dimension is changing. It is alot but one option can be just not desireable but not dangerous... the other can be super dangerous.
If you need to post pics so you can mark/point where you see this grow and when...
I have a few ideas but lets clarify what you actually mean.
Jerry
Yes after firing the shoulder grows forward .020” HS checked with both go and nogo. Also confirmed with factory ammo from Winchester, federal, and Remington. All ended up long. I was thinking it must be overpressure but this is also found with charge weights as low as 41.4gr.
FL sized to saami spec checked against headspace gauge. I also load for 3 other 308 rifles and am pretty particular with double and triple checking measurements both with the rifle I’m loading for as well as looking for any irregularities agains my other rifles in the same caliber so I’m pretty confident they are within spec.
Hmm.. semi-auto.. I don't know much about how that rifle works, but is it possible that the action is either not locking up tight during the firing event or beginning to open while there is still enough gas pressure to cause the case to expand? Have you talked with the tech support at Black Creek about this? There may be a problem with the rifle itself. Adjustment maybe?
I guess you've already Googled this problem, is there any indication others are having the same issue?
What are you getting for pressure signs other than the elongated case?
If you do find the problem, please post what you discovered.
I guess you've already Googled this problem, is there any indication others are having the same issue?
What are you getting for pressure signs other than the elongated case?
If you do find the problem, please post what you discovered.
Mystic Precision
CGN Ultra frequent flyer
- Location
- Summerland, BC
If the headspace is increasing by 20 thou AFTER firing and the sized cases are within SAAMI before chambering, please stop shooting this set up.
something is really off the rails.
The most likely problem is the rifle is grossly overgassed while being under sprung... the action is opening WAAAAYYY too early.
Only by memory but did you ever pick up a just fired case? was it screaming hot?
Brass cases will not tolerate more then 1 firing with this much change in headspace. Attempting to resize and reuse will lead to case separation and other nastiness.
You have a very dangerous situation... get it fixed.
Jerry
something is really off the rails.
The most likely problem is the rifle is grossly overgassed while being under sprung... the action is opening WAAAAYYY too early.
Only by memory but did you ever pick up a just fired case? was it screaming hot?
Brass cases will not tolerate more then 1 firing with this much change in headspace. Attempting to resize and reuse will lead to case separation and other nastiness.
You have a very dangerous situation... get it fixed.
Jerry
Well I feel REALLY stupid right now. I decided to recheck my findings and came to the embarrassing realization I didn’t remove the primers and in my rush to figure out my pressure issue, well you get the idea. Still gotta figure out my pressure signs problem but case length growth is a non issue. �� sorry fellas. Guess it just goes to show you need to take a second and make sure you’re following all the steps.
In a over gassed semi-auto there is still pressure in the barrel when the bolt starts moving to the rear. And this pressure can move the shoulder forward and longer than the chamber.
If your sure of your rifles headspace setting and if the fired case shoulder location is longer than your rifles actual headspace then the rifle is way over gassed.
Do you have a adjustable gas block? If you do shut the gas "OFF" and see what happens to the case shoulder length
You may be using to slow of a burning powder raising your port pressure and need other loading data for a AR10 type rifle.
You can find similar problems in M14/M1A forums where the reloaders are using the Hornady cartridge case headspace gauge. They are bumping the case shoulder back .003 to .006 from the cases fired length and the cases will not chamber.
If your sure of your rifles headspace setting and if the fired case shoulder location is longer than your rifles actual headspace then the rifle is way over gassed.
Do you have a adjustable gas block? If you do shut the gas "OFF" and see what happens to the case shoulder length
You may be using to slow of a burning powder raising your port pressure and need other loading data for a AR10 type rifle.
You can find similar problems in M14/M1A forums where the reloaders are using the Hornady cartridge case headspace gauge. They are bumping the case shoulder back .003 to .006 from the cases fired length and the cases will not chamber.
358Rooster
CGN Regular
- Location
- Central Saskatchewan
Please expand on this. If you're alluding to primers backing out, you still have a problem. It may be headspace, or it may be a gassing / timing condition that Jerry & Big Ed are trying to steer you to.
Are your primers protruding .020?
If they are it also shows the residual pressure from being over gassed can also move the shoulder forward. The amount the primers are protruding shows you how far the bolt moved to the rear with pressure in the barrel. Meaning you can get a false case shoulder length after firing when measuring case headspace length.
It also means if the primer pockets become loose you can end up with a primer ending up in the trigger group and jamming the trigger.
Primers and pockets are staying as they should and aren’t flattened. This bolt has a pretty sloppy firing pin hole and as I’ve experienced with all of my 308s the cci primers are fairly soft so the “crater” is tall by that .020” and with my caliper blade on that crater ridge, that was giving my bad measurements. I do have an adjustable gas block and that was my next thought on where to make some adjustment. Would have done it sooner but as Jerry eluded to, seeing what I thought was a bigger problem I quit shooting it before getting to the gas block. When I have time I will be shutting it completely off and running it manually until I am satisfied I have the rest of the gun running right.
