Case head separation

[Rat Rifle]

To measure for pressure your measuring at the web just ahead of the extractor groove. Even a small base die doesn’t size that far.
Wayne

Ok, then I don’t have a problem … never mind.

 

[ricco1949]

If this is true, then none of us should be reloading. There should be no such thing as a small base die. We should all trash our brass after the first firing.

OK, LETS HEAR IT

IIRC this pressure measurement method only applies to subsequent firings....after the first firing.

I believe Barnes recommended this for their blue coated bullets back in time.....few decades starting to be a little sketchy in the memory bank though.

 

[Will Henry]

Measuring expansion of the solid head of the case, to determine max pressure, is a viable method to show when you have reached the elastic limit of that particular piece of brass. This was once and accepted method for determining a max load. The reason one wants to use once fired brass is that there is some distortion of the head from expansion of the case ahead of that, on the first firing, so you can get a false read.
The thing is, this method is predicated on three things. First, it requires that the brass be consistent in size and hardness. Second, it requires that the chamber dimensions be within tolerance. Third, it requires that the case be the weak link in the system. In other works, it's not a viable system to use to work up loads for your Krag or Lee Enfield.
The brand of brass, and even the lot, can affect the results. Rocky Gibbs used to specify certain lots of GI brass to achieve maximum performance from his cartridges. In commercial brass, he liked Winchester over Remington because it was harder. Rocky wasn't timid when it came to working at the edge, but he was also aware that this method of determining max pressure was absolutely dependent on the strength of the brass.
The point I'm trying to make is that the case expansion method cannot tell you what your pressure is, it can only tell you when it is too high for your particular brass. By the way, if your primer pockets loosen, the head is expanding, and your load is too hot for that brass. WH

 

[Tom S]

To measure for pressure your measuring at the web just ahead of the extractor groove. Even a small base die doesn’t size that far.
Wayne

 

[Tom S]

Not to beat a dead horse, my thought is you will be catching an over pressure load almost immediately, before the primer pockets loosens, saving your brass & preventing premature failure. Your not looking and you won’t get pressure numbers for your load you just looking to stay below excessive pressure or .0005 growth in the said area.

TS

 

[bozo699]

Not to beat a dead horse, my thought is you will be catching an over pressure load almost immediately, before the primer pockets loosens, saving your brass & preventing premature failure. Your not looking and you won’t get pressure numbers for your load you just looking to stay below excessive pressure or .0005 growth in the said area.

TS

Hey Tom,
Not sure what you’re asking or stating for sure. You really don’t want to see any growth but .0005 max, any more than that primer pockets will start to loosen possible extraction issues. I don’t bother with it unless I’m running a opc , changing brass or powder lots. Once I find a load I may periodically check a few pieces. Also not going to lie some of mine has shot better with some pressure signs and I’ve ran them there but not condoning or suggesting anyone does as a matter of a fact just the opposite,…. Stay within pressure limits.
Wayne

 

[bozo699]

Not to beat a dead horse, my thought is you will be catching an over pressure load almost immediately, before the primer pockets loosens, saving your brass & preventing premature failure. Your not looking and you won’t get pressure numbers for your load you just looking to stay below excessive pressure or .0005 growth in the said area.

TS

I reread your post several times and I think the answer is yes you are correct in your thinking.
Wayne

 

[Old Navy]

While .0005" is common on the first firing it not going to stay there for three firings even with Lapua brass. I just starting shooting a new .22 BR. It went to .0015 at three firings and then stayed three for several more reloads. That is one of the reason Harrell's ask for three times fired brass. 105 Bergers over 30 grains of Varget seems to be the normal safe load for a lot of folks here. Try it for yourself.

 

[moe africa]

I measured up the cases again with a caliper and headspace comparator
My bump is between 2-3 thou inch
Interesting thing I noticed that the cases with signs of separation, measured 2 thou longer than my fired brass

 

[Dolomite]

I measured up the cases again with a caliper and headspace comparator
My bump is between 2-3 thou inch
Interesting thing I noticed that the cases with signs of separation, measured 2 thou longer than my fired brass

on the cases with signs of separation did you have a heavy bolt lift? It could be you were bumping the shoulders too much if you don't get a heavy bolt lift.

 

[novice]

Do you know the unfired length of the cases?
Yes, accumulated stretching and bumping can lead to a separation.

 

[BoydAllen]

Measuring expansion of the solid head of the case, to determine max pressure, is a viable method to show when you have reached the elastic limit of that particular piece of brass. This was once and accepted method for determining a max load. The reason one wants to use once fired brass is that there is some distortion of the head from expansion of the case ahead of that, on the first firing, so you can get a false read.
The thing is, this method is predicated on three things. First, it requires that the brass be consistent in size and hardness. Second, it requires that the chamber dimensions be within tolerance. Third, it requires that the case be the weak link in the system. In other works, it's not a viable system to use to work up loads for your Krag or Lee Enfield.
The brand of brass, and even the lot, can affect the results. Rocky Gibbs used to specify certain lots of GI brass to achieve maximum performance from his cartridges. In commercial brass, he liked Winchester over Remington because it was harder. Rocky wasn't timid when it came to working at the edge, but he was also aware that this method of determining max pressure was absolutely dependent on the strength of the brass.
The point I'm trying to make is that the case expansion method cannot tell you what your pressure is, it can only tell you when it is too high for your particular brass. By the way, if your primer pockets loosen, the head is expanding, and your load is too hot for that brass. WH

For the other readers, one advantage of loading at the range is that you can take one case and load it several times to see what the effect is on the primer pockets. There are a lot of other advantages, but this one is worth mentioning. Also, harder brass is stronger, and if you can harden it a bit, you will have made it a bit stronger. One successful F Open shooter has said that for new brass he uses a load that is the next node lower than his usual one. This hardens the heads and he gets longer brass life out of the hotter loads than shooters who start out with their normal hot load. I spoke with a production manager of one of the fancier brass manufacturers, who had spent 12 years working in brass production for Remington, and he confirmed that this approach works. For measuring solid head expanion the classic tool is a blade mic. They can fit into the bottom of the extractor groove on most cases.