Primer pockets shrinking?

[cuesandmore]

A friend of mine says primer pockets shrink upon firing. He uses a primer pocket uniformer on new brass before reloading. After firing he uses it again before reloading. He says he gets brass every time he uses it. Therefore the pockets shrink when the cartridge is fired. I say he is nuts. What do you all say?

 

[Blue68f100]

If that was the case we would never loose brass to loose primer pockets. I'm with you. He's not using the tool correctly. Not square and cutting the sides away.

 

[ReloaderFred]

Deleted. Not pertinent....

 

[Walkalong]

Pressure will push brass into the bottom of the pocket, that is where he is getting brass from. They are not shrinking. Primer pocket uniformers only remove brass from the bottom of the primer pocket, squaring up the bottom.

 

[Toprudder]

I saw an article some time ago about the effects of multiple firings on brass - specifically .45acp. The length of the brass shrunk, and it was determined that the head of the brass was being compressed slightly with each firing. It that is true, it would make sense that the pocket depth would shrink. A uniformer removes brass from the bottom of the pocket, not the sides.

 

[cuesandmore]

If pressure is pushing the brass back to the bottom of the primer pocket, why after multiple firings don't I get high primers? Same load in both guns. Is it that slight?

 

[1KPerDay]

It is a very small amount. Hard to tell the difference between a thousandth or two. And your loads might not be hot enough to really make a significant impact.

 

[Schwing]

I have, personally, never experienced a primer pocket that became tighter after being fired... Lots that get looser though.

 

[Walkalong]

Yep, they can be loose after firing and still get some brass off the bottom with a uniformer.

 

[Ole Joe Clark]

It's .000000025 shrinkage per shot if the sun is shining, somewhat less if it's cloudy and below 40° F.

 

[murf]

yes. i uniform primer pockets after every firing and get brass shaving on almost every one. there will be a shiny ring around the outside edge of the pocket base and a small shiny ring around the firing pin hole.

murf

 

[Wis-Harpo]

I just bought a primer pocket uniformer due to posts on TRH. I sized 50 new Starline 47-70 brass some time ago and have not primed them yet. I was under the assumption that the uniformer only had to be used once on the primer pockets. I used the advice here and bought one with a set stop rather than an adjustable one.

 

[murf]

I just bought a primer pocket uniformer due to posts on TRH. I sized 50 new Starline 47-70 brass some time ago and have not primed them yet. I was under the assumption that the uniformer only had to be used once on the primer pockets. I used the advice here and bought one with a set stop rather than an adjustable one.

you actually don't have to use one at all. most people get by without one. but i use mine every time i prep cases. the first go-around can remove a lot of material from the bottom of the pocket. the second go-around usually only takes a tiny amount from the bottom. most only do the operation once and that takes care of any shallow pockets for the life of the case.

luck,

murf

 

[spitballer]

Not surprised. I've always suspected this with moderate loads and thin-cupped primers.

 

[mdi]

Nuts...

Although I've read a theory on semi-auto handgun brass getting shorter over time. According to the author the driving the brass against the bolt face will shorten the distance in the extractor groove. If this happens, perhaps the "peening" and resulting shortening, displacing metal could flow into the primer pocket. Nah...