Thoughts on partial case separation

[gunsandgunsmithing]

Ya... I was thinking after I ordered the no-go that I should have ordered the field gauge instead.

Jmho, but if it left the factory outside of a no-go, it should be taken care of but they "could" see it differently is all.

 

[searcher]

I had a chamber cut for a .20 Practical a number of years back and an uncleared chip or something put a gouge on the inside of the chamber, about 3/4 of the way up the case. The line (a 1/16th" wide ring) that is left around a fired case is noticeable and I was worried that it would greatly shorten the life of my brass fired from that particular A/R. That turned out to be not true - and I have gotten the normal 8 to 9 loadings on the brass over the life of that barrel. The primer pockets give out before any problems associated with the "ring" left by the scratched chamber have manifested.

 

[doninreno]

I've spent a good deal of time CAREFULLY examining this case stretch problem/question and there is one thing that I have found to greatly affect your measurements when comparing brass (fired vs unfired vs just been run through a sizing die) and THAT is the presence of a primer or no primer and then fired brass with a primer in it still and also a piece of fired brass without a primer but not yet been through a sizing die (so it is pretty close to the size of the chamber it was fired in). From many years of shooting and reloading, I have found that some (many) firing pin to bolt face hole size (for the firing pin to pass through) clearance combinations can leave a slight "crater" effect with a rim around it that stands slightly proud. MANY box stock rifles produce this "crater rim".....Now, I am NOT saying that this is a bad sign or anything like that! Many things can contribute to this effect including firing pin shape, pressure inside the bass upon firing, hard vs soft primers etc, etc. that are NOT signs of excessive pressure, BUT if you're trying make measurements for use in comparisons BE SURE THAT you don't have a fired primer still in the primer pocket (possibly with a with a crater and rim) as its presence can easily throw your measurements off around .004" to .OO5" and THAT will screw up all of your headspace calculations!

A second thought here is that some primers "back out" some when the round is fired and that can contribute to the "rim" around the primer strike being even higher than is the one on a primer didn't back out. Watch for that one, too!

After finding this to be something that skewed my measurements by enough to make my efforts kind of useless, I became VERY careful to be comparing apples to apples and oranges to oranges....that is to say...be sure that all cases used in measurements/comparisons of case size/headspace numbers MUST be the same and the best way to do that is to ALWAYS be sure that the primer is either seated to be below the face of the case OR to be not there!!

This has led me to pretty consistent headspace in my rifles after reloading and has led to longer case life and fewer case failures.. A tip to consider is to use Redding shell holders that are called a Competition Shellholder Set (or something similar) and they come calibrated in .002" inch steps. As an example, I use the Size # 01 set for my 6mm BR reloading (the number 01 is for standard shells such as 308, 30-06, 270, etc. And is, in essence, a "#3 shellholder substitute for use in your press.

 

[gunsandgunsmithing]

I've spent a good deal of time CAREFULLY examining this case stretch problem/question and there is one thing that I have found to greatly affect your measurements when comparing brass (fired vs unfired vs just been run through a sizing die) and THAT is the presence of a primer or no primer and then fired brass with a primer in it still and also a piece of fired brass without a primer but not yet been through a sizing die (so it is pretty close to the size of the chamber it was fired in). From many years of shooting and reloading, I have found that some (many) firing pin to bolt face hole size (for the firing pin to pass through) clearance combinations can leave a slight "crater" effect with a rim around it that stands slightly proud. MANY box stock rifles produce this "crater rim".....Now, I am NOT saying that this is a bad sign or anything like that! Many things can contribute to this effect including firing pin shape, pressure inside the bass upon firing, hard vs soft primers etc, etc. that are NOT signs of excessive pressure, BUT if you're trying make measurements for use in comparisons BE SURE THAT you don't have a fired primer still in the primer pocket (possibly with a with a crater and rim) as its presence can easily throw your measurements off around .004" to .OO5" and THAT will screw up all of your headspace calculations!

After finding this to be something that skewed my measurements by enough to make my efforts kind of useless, I became VERY careful to be comparing apples to apples and oranges to oranges....that is to say...be sure that all cases used in measurements/comparisons of case size/headspace numbers MUST be the same and the best way to do that is to ALWAYS be sure that the primer is either seated to be below the face of the case OR to be not there!!

This has led me to pretty consistent headspace in my rifles after reloading and has led to longer case life and fewer case failures.. A tip to consider is to use Redding shell holders that are called a Competition Shellholder Set (or something similar) and they come calibrated in .002" inch steps. As an example, I use the Size # 01 set for my 6mm BR reloading (the number 01 is for standard shells such as 308, 30-06, 270, etc. And is, in essence, a "#3 shellholder substitute for use in your press.

You bring up a good point Don. It's easy to forget about something that basic but if you don't address it, you are very likely to get bad measurements. I often drag the case head with the cratered primer or even one that looks fine, across a file for a couple of swipes or so. Just enough to make sure the surface of the case head is flat all the way across. Not really removing any material on the case itself but just enough to see that nothing can hold the case proud for whatever reason. Won't hurt a thing and can prevent a headache.

BTW, is this Don Lahr by chance? If so, how ya been doing?

 

[doninreno]

Nope. Johnson. And I don't have a red Ferrari nor do I have a pink sports jacket.

 

[gunsandgunsmithing]

Nope. Johnson. And I don't have a red Ferrari nor do I have a pink sports jacket.

Funny! Don Lahr is a good bullet maker. He moves around a lot but last I knew, he was in Nevada somewhere...I think near Vegas though.

 

[doninreno]

Could be. I have never heard of him, but Las Vegas is a 7 hour drive from Reno even if you haul *ss!