I have yet to start reloading, but I have been saving all my 10mm brass.
Last night, I fired most of a box of Armscor ammo- 180gr fmj.
I noticed that even though these are lower power rounds than the Sig Elites I was firing earlier this week, the spent cases looked even more bulged than those of the Sig.
Now, when I say "bulged" I mean a slight swelling near the web. Maybe .010"-.015" larger than the original diameter. Noticeable, anyway.
I just miked unfired Armscor ammo, Sig ammo, and for the heck of it, pinned my chamber.
Sig ammo diameter at the web: .4215"
Armscor diameter at web: .4182"
1006 chamber at .250" from breach face: .429 +/- .0005"

SAAMI specs say that part of the case should be .425" +0 -.005"
And the chamber at .200" from breach face (I went .050" more to clear the feed ramp) should measure .4281" +.004 -0

So, there's a full .010" air space in my chamber when using Armscor?
Doesn't seem like much, but I typically work with tolerances down to .00005" for my work, so .010" is enough room to build a stadium in my eyes..

I know .002" under tolerance wasn't the only factor in these cases warping and expanding, but I'm not buying the Armscor again I don't think.

Anybody else experience this?
Is it going to be worth me keeping these cases for future reload?

Here is new Armscor as measured Case: Diameter 0.4200" Crimp Diameter 0.4220"  New Starline Brass  usually is 0.4215"
Armscor is small and they are using uber fast powder Tight Group  6.4 grains, fast powders can have pressure spike that can be extreme and not good on the brass...

S&W chamber is  0.4285"  not a bad chamber size
Glock chamber is 0.4340"  Loose for combat reliability

My handloads run .422 when measured .225" from the base.  They measure .419 measured .400" from the base.

Your Armscor and Sig ammo are within .003" of each other, so I would not stress about this.

The real question is how well they reload and hold up over time.

Thanks, Shadow and sqlbullet.

This particular batch are just running on the low side. Didn't think it was a major issue.

And don't Glocks tend to have a less supported chamber? From what I've read, anyway.. This brass probably looks stellar by comparison..