Over sized chambers on 7.62x39 weapons

[Show Me]

Nothing exciting. Wondering what others have seen. Since I can't put away my latest project I've measured brass from both my mini thirty and my Ruger American.

When new or fully sized brass is fired in both rifles it grows a consistent. 013. And at the case head it swells. In modern times with computer machining why would they do that.

I deal with the same thing on some Garands. I size back with a .010 over shell holder. Gives me .009 or .010 over depending on the individual piece. For .004 head space.

I remember years ago the lacquered ammo that would stick in a hot chamber if you had a pause in the blasting. (Not a blaster for years now) maybe they do that because they don't know what someone might shove in the chamber. Arms manufacturers couldn't care less about reloaders.

So I thought maybe some might give their take on this.

 

[nettlle]

Fired rifle brass will swell and grow. Regardless.
The chamber is larger than the sized brass. Or should be for easy chambering.
What are you trying to fix?

 

[Blue68f100]

The length part growing you can control with not pushing the shoulder back as far during sizing. On a bolt gun you only need 0.001"-0.002", with a simi-auto you need 0.002"-0.003". Doing this will greatly increase your brass life.

Now if you have a set of case gauge and it shows the chamber is out of spec Ruger should take care of it. Now this only checks the shoulder position.

 

[Lefty38-55]

Yes, I too think you're pushing your shoulder too far back. Look up Larry Gibson's article on using the special RCBS 'X' Sizing Dies to reload for the M1A. Typically he'd toss the cases after 3 or so firings, but using the X dies per the instructions, he tested them up to 16 reloads per case when he stopped the test, as the premise was proved; i.e., that the X dies do inhibit case length growth.

 

[jmorris]

When new or fully sized brass is fired in both rifles it grows a consistent. 013. And at the case head it swells. In modern times with computer machining why would they do that.

"They" are only doing that to the new brass, the sized brass is on you.

There are tolerances in everything (+/- x.xxxx), they just made sure their chamber would accept anything within the range. Makes sense for ammo MFG's to try and end up on the small end of the tolerance and barrel chambers, the large.

If we move the ammunition to the large side and the chambers to the small, one not going into the other is more likely. People complain more about that, so that is what they are trying to avoid. Especially if they know to set their size die, to get the results they are after, after the first firing.

 

[243winxb]

at the case head it swells

More then .448" & .405" ? Measure fired brass.

 

[Show Me]

Yes, I too think you're pushing your shoulder too far back. Look up Larry Gibson's article on using the special RCBS 'X' Sizing Dies to reload for the M1A. Typically he'd toss the cases after 3 or so firings, but using the X dies per the instructions, he tested them up to 16 reloads per case when he stopped the test, as the premise was proved; i.e., that the X dies do inhibit case length growth.

Ya ok

 

[243winxb]

Not asking for help. Not asking for specs. Not wanting to fix. I plainly stated I've discovered an issue and have measured and adjusted for success

Please share your expertise on the topic. What was the measured diameter of the fired brass?(as ask above.)
Help us all learn with your wisdom.

 

[Show Me]

Please share your expertise on the topic. What was the measured diameter of the fired brass?(as ask above.)
Help us all learn with your wisdom.

Wonder why you quoted me but didn't answer my question.

 

[Show Me]

"They" are only doing that to the new brass, the sized brass is on you.

There are tolerances in everything (+/- x.xxxx), they just made sure their chamber would accept anything within the range. Makes sense for ammo MFG's to try and end up on the small end of the tolerance and barrel chambers, the large.

If we move the ammunition to the large side and the chambers to the small, one not going into the other is more likely. People complain more about that, so that is what they are trying to avoid. Especially if they know to set their size die, to get the results they are after, after the first firing.

That's fine but did you get the .012 to .013 head space part of my decreption. Do you measure chamber's and head space on many types of rifles. My Garands aren't this loose. That's why I only asked if anyone else has measured this.

 

[Show Me]

Yes, I too think you're pushing your shoulder too far back. Look up Larry Gibson's article on using the special RCBS 'X' Sizing Dies to reload for the M1A. Typically he'd toss the cases after 3 or so firings, but using the X dies per the instructions, he tested them up to 16 reloads per case when he stopped the test, as the premise was proved; i.e., that the X dies do inhibit case length growth.

Grows .013 and I push it back to get .004 head space. How is that too far. X die has nothing to do with what I described

 

[Show Me]

TMI. Done

 

[GHinNH]

Let me begin by cherry picking your words and quoting you just to set the mood, then I'll begin asking you questions instead of offering an answer to yours... It never ever fails, which is why I seldom ask questions.

To suggest an answer, I think you're pretty close with old steel ammo, as designed that's the only thing they ran, Only since reloading became a thing do we use brass cases and save them.

Purposeful design for all conditions from Siberian winters to 110% humidity jungles with single use ammo. They also came only in one flavor that included a third position safety selector so stopping to clean the rifle was not an option. Pretty much the cast was set decades ago and theirs no turning back now...

There's more to unpack but that would take all day....

If it were me, I'd cast the chamber with Cerrosafe, it would nag at me forever if I didn't.

 

[jmorris]

When new or fully sized brass is fired in both rifles it grows a consistent. 013.

Are you saying, you measure case length, then fire the round and it blows out AND gets longer?

Or are you firing it, then upon resizing, it gets longer?

 

[Show Me]

Are you saying, you measure case length, then fire the round and it blows out AND gets longer?

Or are you firing it, then upon resizing, it gets longer?

Thanks for asking. The chamber is so oversized on both the bolt and autoloader that measuring after firing they show .012 to .013 thou growth. So I use a .010 over shell holder and verify 2 to 3 thou bump back. Then the lead is so deep I'm at .035 thou over max length. Touches at .065 thou over length. That's the best I can explain.

So tonight I set up at 50yds because I still don't have this new knee broke in. 50yds is fine for these kid guns that won't shoot past 125.
Scoped bolt gun made one hole 5 shot group. The mini with a red dot shot three pretty close for that picky rifle. So I'm getting somewhere like I did with my Garands. good first test.
So I was wondering if others have found oversized chamber's in their mass produced rifles or does anyone even check when they have one that won't shoot so good.
You can adapt and over come. Thanks again for asking.
A custom barrel for each with a proper chamber would be nifty but these Rugers are too cheep for that.

 

[Show Me]

PS. This is why I got the Wilson case checker for x39 to go with my mic to see how much I was resizing. Very educational

 

[jmorris]

Thanks for asking. The chamber is so oversized on both the bolt and autoloader that measuring after firing they show .012 to .013 thou growth. So I use a .010 over shell holder and verify 2 to 3 thou bump back. Then the lead is so deep I'm at .035 thou over max length. Touches at .065 thou over length. That's the best I can explain.

What is the starting case length, case length after being fired and after being fired and sized but not yet trimmed?

 

[Show Me]

What is the starting case length, case length after being fired and after being fired and sized but not yet trimmed?

I'm measuring from datum line with a Wilson case checker and a Wilson mic. Not measuring over all case length. Such low volume they get trimmed and cleaned each time.

 

[Show Me]

Fired rifle brass will swell and grow. Regardless.
The chamber is larger than the sized brass. Or should be for easy chambering.
What are you trying to fix?

Thanks for your question. Between pain pills and the therapy torture lady I lost track of this. I always measure brass to check out chamber's since while reloading we can control amount of resizing. Target and hunting rifles I cut it close. Autoloaders slightly more space.

Well, when I got into Garands one built from a kit of parts and one with a new barrel , both have eleven to twelve thousands brass growth. I use a Redding. 010 shellholder , works perfectly. Peterson brass lasts a long time.

Mini thirty has the same oversized chamber. Brass grows. 010. Full sized brass shoots patterns like some people report.
When I use blown out brass it shoots much better.

Post #1 doesn't ask about fixing anything. Don't know how that got started.

 

[Show Me]

Please share your expertise on the topic. What was the measured diameter of the fired brass?(as ask above.)
Help us all learn with your wisdom.

Did you read the first post. It's not a debate. Statement of facts and a question of what others have seen.

 

[Walkalong]

TMI. Done

As you wish.


Better questions and better responses to posts get better answers, help those trying to help you.