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Discussion Starter #1 (Edited)
Hey guys, ran across something and ended up down a rabbit hole i didnt expect today. hoping to share this and collaborate with you all.

try to keep the story part short.
i was sorting through my brass and came across some 7mm mauser brass my brother had given me after he shot it with a bunch of other brass he collected. he inherited an old military surplus rifle from our grandfathers collection that was unmarked. i Took said rifle and another one that was unmarked to a "gun smith" to have the chambers miked cause you tend to want to verify the caliber before you pull the trigger. said smith claimed one was a 7mm mauser and the other a 6.5x55 swedish mauser.

i didnt think anything of it and sent the gun on its way with my brother.

since all this happened ive put a few years of reloading under my belt, my general experience has been that bullet cases tend to come out of the chamber looking uncannily similar to how they looked when they went in to be fired, with some marginal differences usually only notable with a micrometer measuring in the thousands of an inch.

having not ever touched a 7mm mauser round before i didnt question the odd shape of the brass when he gave it to me other than noting that it was odd shaped, away it went in the scrap bucket.

back to me sorting through brass. i noticed the primers were backed out of the 7mm cases he gave me. googled it and it apears to be a common problem in surplus military 7mm mauser rifles, headspace issue. then i googled 7mm mauser ammo cause my brother said it was expensive. turns out its not from the sites i found it at but... red flag... the fired cases i have look NOTHING like the cartridges on these websites that are stamped 7mm mauser.

into my sierra reloading manual i went. 7mm.jpg this piece of fired brass meets NONE of these measurements. This brass is headstamped 7mm mauser, and best i can tell that means 7x57. but none of the measurements match up. the only measurement i could get to sync was where the shoulder used to be. at 1.728 as shown in the sierra manual picture the dark line on the case right above the 3.065 maximum word... that dark line measured from base to dark line=1.728. and its obvious that the case is missing a lot of neck. the over all case length of this fired piece of brass is 2.206. thats a lot of shrinkage.

I do understand that a case doesnt exactly fire form to a chamber and especially in this case we cant guarantee that we can determine the caliber of this round by going off the new fire formed case dimension but i wanted to try and see how close i could get.

well. i started with the case mouth. new dimensions are .310 i.d.; like for a .308 calibur bullet. sierra says it should be .284: o.d. is .340 sierra says it should be close to .321
next i measured to the shoulder 1.921 sierra says it should be 1.728 which is where that dark line is.
i measured right on the web .463 sierra says it should be .471

well ****. this explains the headspace issue and why my brother complained it was innacurate. at the time i chalked it up to a shitty barrel and a potentially worn out crown. ( a different smith put a bore scope down both mausers, didnt look good, pits and other issues)

i then rifled through the other 30 caliber potential suspects and landed on the 30-06 as the closest contender. i also happened to have a few pieces of 30-06 brass. 7mm fired v 30-06.jpg

i know in these types of situations its not safe to jump to conclusions and we should probably cast this bore to be sure. however. the dimensions of this fired 7mm mauser brass are within 5 thousands from base to the shoulders and within 1 or 2 thousans every where else measurable to this 30-06 brass.

what are your guys thoughts guys?

anyone elses 7mm mauser brass come out of their gun looking like this?
 

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First off, your "gunsmith" is a moron. Secondly, if that brass was originally 7MM Mauser, you are shooting itt out of either a 30.06 or a wildcat using 30.06 cartridge necked down to 7MM (.284) which was a popular wildcat in the day. Known as 7mm-06. In any case DO NOT continue shooting 7X57 ammo in this gun! Go to a real gunsmith to do a chamber casting.
 

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Discussion Starter #3
Thanks for confirming my suspicions, my brother has since sold this rifle to a "collector" whatever that means. i will be ordering some Cerrosafe to cast the chamber of the "6.5x55 swede" cause i dont believe its what he said it is.
 

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I hope your brother warned the buyer on this. There was a guy at my range a few years ago that bought an Arisaka sporter from a guy who "thought it was a 30.06" When he rammed the bolt on a round it detonated and blew the bolt into his shoulder (thankfully he hadn't put his face down yet). He bled like a stuck pig but was not seriously hurt.
 
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