How to measure COAL with Bullet Comparator

The way I tell if a gas gun has an out-of-square bolt face is I use the trimmer on my Wilson case trimmer to hold the case backward and concentric and touch the case head. It's 1/2 wide and if it cleans one side before the other, the head has been fire formed out of square by the bolt face. I got lucky with both my M1A and my DCM Garand, as the Wilson marks their heads both evenly. A couple of other Garands I have for as-issued matches didn't do so well, and the as-issued rules don't let you do very much to the gun, so that was catch as catch can.

Whether or not you notice concentricity is partly about bullet length and shape. Short ogive, long-bearing surface bullets don't have room to tilt much in the bore. By way of comparison, Harold Vaughn got 0.004" of bullet tilt in a 6mm to open groups about 1/3 as much as A.A. Abbatiello measured it to do with the .30 cal M1 Type bullet.
 
Unclenick,

Are the "as issued" matches you mention different than EIC "leg" matches where external modifications are not allowed?
 
Unclenick,

Most of my loaded ammo off my Dillion RL550 is right around 1 thousandths runnout. The redding Competition seater die you recommend has greatly reduced my runnout.

Side note,

I noticed with my hornady concentricity tool that you can adjust the runnout but it drastically increased my group size because I think it was varying my neck tension. So lesson learned I reduced the runnout during the reloading process by getting a better press and better dies..
 
It's too bad that a given crooked cartridge will have different runout numbers across all runout gauges and how they are set up.

Some people have noticed velocity is less after straightening cartridges with Hornady's tool. I asked Hornady about that and they said that won't happen. In my tests, bending the bullet reduced the force needed to push it out of the case neck because it was gripped less by the case neck.
 
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Bart B

Same exact thing happened too me I could make almost perfectly concentric ammo but groups were worse than before. Stop using the adjustment and groups shrank drastically. It was killing my neck tension

I believe if its 2 thousandths or less the barrel actually straightens the bullet out , I watched a video by Erik Cortina and he said he isnt worried about run out at all so I figured I would just trust my seating die and I use the tool every so often to check it.

I use to sort ammo by run out not anymore it really didnt make a difference
 
Same here, I don’t use the tool to correct slightly less than perfect concentricity. I’ve also fine tuned my method to where 99% of my loads are under .002” or most of the time under .001”.
 
yes, changing to a competition seating die and using lyman m neck sizer die drastically improved my concentricity and seating depth which in turned shrank group size. I still use a slight taper crimp at the last stage but thats an old worn out subject for another time.
 
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