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Old February 5, 2013, 10:20 AM   #10
Slamfire
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Join Date: May 27, 2007
Posts: 4,110
I really think small base dies are a safety critical issue for Garands/M1a's and even M1 carbines.

Standard sizing dies sometimes do not always reduce a case enough to drop in the chamber.

Gene Barnett cut me this reamer cut gage. He also cut me a 30-06 reamer cut gage. These gages are exact duplicates of the chambers of the match rifle barrels he cut as he used the same chambering reamer to cut these gages.

Wilson gages are excellent for their purpose: to measure length from shoulder to base. Wilson gages are cut large between the shoulders so that you can drop a fired case into the gage and get a very good idea of the headspace of a bolt action. It does not work for a gas gun, because cases are stretched during extraction in a gas gun. But, the limitation of these gages is that they don’t measure “fatness”.

The reamer cut gage will display “fatness”.

Range pickup cases unsized. One falls into Wilson gage, as expected, the other will not drop into reamer cut gage.






Case sized in Lee Die


Lee Die sized case does not drop into reamer cut gage.

Small based sized (actually sized in an RCBS small base die) drops all the way int.


I also bought reamer cut gages from Compass Lake Engineering http://www.compasslake.com/. Frank has a number of barrel stubs that he will cut with a chambering reamer to make you a reamer cut gage.

I will say that most of my range pickup cases dropped into the reamer cut gage after sizing in the Lee die, but you will run across fat cases in range pickups or once fired military cases.

But to continue pounding on this subject, but without additional pictures, is something happens when you stuff a bullet in the case. This is something that is not appreciated till you get gages, is there are dimensional changes when you stuff a bullet in the case.

My second out of battery slamfire, occurred with 30-06 cases which were sized in a Bonanza NM sizing die. That die sized cases down more than my RCBS standard but not as much as a small base die. I did not have small base dies at the time. Each of the Bonanza sized cases would drop into the reamer cut gage. But when I reloaded the things with powder and ball, and tested them by dropping them into the reamer cut gage, rounds stopped basically at the location you see in with the standard based sized 308. I sort of tossed it off because conventional wisdom was that only high primers and worn receiver bridges caused slamfires. To prevent high primers I had individually reamed each primer pocket to depth and inserted a Federal Match primer by hand and visually inspected each case to see that every primer was well below the case head. I reamed the pockets to an excessive depth, probably 0.006 to 0.008” below the case head in the errant belief that if high is bad, then really low must be good. Events showed the fallacy of that theory. I was sighting a new NM Garand with a new Barnett barrel. The receiver was cherry and the parts were virtually new in the box GI. That Garand slamfired out of battery, from the clip, and blew the back of the receiver heel into my face, busting my shooting glasses and cutting my cheek.

Except for the receiver, I am still using all the other parts from that rifle, including the trigger mechanism, and winning once a year “Garand” matches with the reconstituted parts. My trigger mechanisms have never followed.

There are a few things that can be learned about this 1) primer sensitivity is always important 2) cases change dimensions after you seat a bullet 3) even a slight interference fit increases the risk of an out of battery slamfire.
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