I used to turn off the gas cylinder spindle valve and "fire-size" my match brass. and manually extract it from the chamber after a few seconds of cool-down.
That was in the days when I shot local matches. I would then use the RCBS case measurement gauge to get a numerical idea of my chamber dimensions and adjust my sizing die accordingly. Worked ok for my level of (non) proficiency
Sizing and/or measuring off an automatically-extracted case won't give you an accurate picture of the chamber due to the extremely close timing of the firing-extraction cycle in the M14
since extraction begins before all the gas pressure has left the barrel,,,,the case still has not fully relaxed its grip on the chamber walls........... the result is case stretch when the bolt starts yanking the brass out ...
which results in bad (oversize) readings of the chamber dimensions
all fun stuff....
the only consideration I would have in how you are backing into the the proper chamber sizing is the potential for case neck stretch from the expander ball in the die...
with repeated sizing to get the shoulder right, you could be tugging at the case neck with the expander ball which might give an off-reading.
If the case is trimmed back to 2.005 and you get a good shoulder before it pulls/stretches beyond 2.015 you should be OK.
Also....keep in mind that you have sized and resized one piece of brass down to the dimension you want. The next fresh case you size may not behave the same way when run through the "adjusted" die just once.
If you want to get really deep into this you can have a chamber casting made and have one of the die makers machine a sizing die to your desired/exact dimensions
At the end of the day I simply cannot out-shoot most of the M14 types I have put together...they are always better than I'll ever be so I need to draw the line somewhere...or move over to rail-guns in 6ppc
That was in the days when I shot local matches. I would then use the RCBS case measurement gauge to get a numerical idea of my chamber dimensions and adjust my sizing die accordingly. Worked ok for my level of (non) proficiency
Sizing and/or measuring off an automatically-extracted case won't give you an accurate picture of the chamber due to the extremely close timing of the firing-extraction cycle in the M14
since extraction begins before all the gas pressure has left the barrel,,,,the case still has not fully relaxed its grip on the chamber walls........... the result is case stretch when the bolt starts yanking the brass out ...
which results in bad (oversize) readings of the chamber dimensions
all fun stuff....
the only consideration I would have in how you are backing into the the proper chamber sizing is the potential for case neck stretch from the expander ball in the die...
with repeated sizing to get the shoulder right, you could be tugging at the case neck with the expander ball which might give an off-reading.
If the case is trimmed back to 2.005 and you get a good shoulder before it pulls/stretches beyond 2.015 you should be OK.
Also....keep in mind that you have sized and resized one piece of brass down to the dimension you want. The next fresh case you size may not behave the same way when run through the "adjusted" die just once.
If you want to get really deep into this you can have a chamber casting made and have one of the die makers machine a sizing die to your desired/exact dimensions
At the end of the day I simply cannot out-shoot most of the M14 types I have put together...they are always better than I'll ever be so I need to draw the line somewhere...or move over to rail-guns in 6ppc
