Acceptable case expansion ?

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Archer Sam

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What is an acceptable amount of expansion in the web area on factory ammo? If the case expands 10 thou over the unfired factory ammo size would you consider this excessive? The rifle has been checked and head space is correct.
I have seen other cases in same cartridge fired from same manufacturer in another rifle from the same maker and measurements weren't the same.
 
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Caliber?

It varies. A lot.

Download and compare the dimensions of a minimum size cartridge, to a maximum size chamber, and you will see what the manufacturers aim for.

Some of the older cartridges are very loose compared to a modern one, but it still can be a pretty big diff between what the case starts out at, and where it ends up.
 
Rifle is a Ruger American Predator
Before fire is.4655
After was .4755 IIRC(corrected)
I don't have any of the fired cases in front of me. Were sent with the rifle.
 
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I don't have the fired case in front of me. I know it was 10 thou bigger. It must have been .4755 then. Gunsmith said the cases were 8 thou larger than unfired by his measurement. Guess I put the wrong number in here.
The cases I resized only went back to .4715
The brass from another Ruger I resized at the same time measured .4705
 
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Ken Waters didn't like to see any more than a couple of thousandths per side meaning anything over four thousandths of an inch expansion was cause for alarm. There were exceptions in the semi autos that broke the rule but his values were based on the re-loaders perspective. If you shoot only factory ammo and don't care to fuss with hand loading then live with it, otherwise you have reason to stir up some dust. D.H.
 
You need to compare the saami spec measurements for the chamber to the fired brass... often some manufacturers make some brass considerably under size and every one of them looks terribly bulged when fired in a normal acceptable chamber.
 
I would call that chamber oversized. I would have to look at the SAAMI specs to know if it is officially over but I suspect it is.
 
OP it's entirely possible for rifles from the same manufacturer to have slightly different chamber dimensions. Even in this day of CNC machining.

Chambers are cut with reamers. Reamers are intentionally cut to give close to maximum chamber dimensions so they can be sharpened when they get dull, rather than thrown out. It's all about keeping costs down.

As the reamer gets sharpened the chambers it cuts get slightly smaller. When the reamer reaches the point that the chamber will be under SAAMI specs it is scrapped.

Without seeing your cartridge it's a tough call. You may have a chamber right on Max SAAMI spec or one thats had the reamer pushed forward a few thousandths to far. Have you compared the other dimensions to see if the shoulders have been pushed ahead as well??? Are you getting protruding primers???

Just not enough information.

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If the stretching is circumferential and you are having no issues with extraction or split cases along the length of the case than I wouldn't worry too much about it.

If you're experiencing longitudinal stretching and it's progressive than you could have an over pressure situation due to severe fouling. You might notice a pronounced indentation of the extractor on the base of fired cases as well.
 
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