How to measure shoulder bump without rcbs precision mic?

Jed Eckert

Well-Known Member
Joined
Sep 21, 2019
Messages
57
Location
Left Coast
Howdy,

I use an rcbs precision mic setting my FL die for .30-06
Contemplating getting into a caliber that rcbs does not make a precision mic for
how do I adjust the die to only bump
.001?
Are there other tools out there?
thanks
 
To compare fired to sized brass, you just need a case that touches near the middle of the shoulder. Remove primer, square case mouth.
30-06 comparator_zpsnqfwilzp.jpg
 
243winxb, below is a .40 S&W case on a .223 case, now what do I do. (a "little" case humor) :)

kQTWyvB.jpg


Wait a minute, I have the Hornady cartridge case headspace gauge that works on any rifle case. And you can even calibrate it to read actual headspace.

Below a Colt 5.56 Field gauge at 1.4736

MLSZTeH.jpg


Below the same Colt Field gauge in my adjusted Hornady gauge.

kkoU6og.jpg


Below a "FIRED" Lake City 5.56 case in my Hornady gauge.

OJqNmQH.jpg


Below my RCBS .308 Precision Mic I haven't used since I got the Hornady gauge.

fXsKe7r.jpg


Advantage, the Hornady gauge because one size fits all.
 
Last edited:
The reasoning behind .002 to.003 is because you get various spring backs on your sized cases. If you only do .001 and the brass stays perfectly put your good. But if it springs back then it's not going to have clearence. Anytime you feel the bolt closing hard on a brass there is going to be verticle in your group. By going to .002 or .003 you still have clearence if you get a few cases that spring back a little. I always use.003 myself. I know a current world record holder that bumps .008. he likes his brass loose.
It obviously works for him.
Shep
 
Normally I use the RCBS Precision Mic. And I have both the Hornady and Sinclair comparators, take at least 10 readings with each, then average them individually, and have two references. I also have a Willis Innovative technologies Digital Gauge as another reference source. I recently picked up a Forster Datum Dial kit and suspect it will give me fourth tool. I am able to get pretty close with any/or all of these. And yeah, I am a bit of a gadget freak!
 
I use the method that Jim See posted somewhere. I resize, put a piece of scotch tape on the case head, and try to chamber the case. You have to work the die down gradually. When the bolt will close on the case with tape on the head, you have your clearance.

Note, test each adjustment on a different case to prevent work hardening. Then once the die is set, set the shoulder back on all the test cases so they are only sized twice.
 
Ok, I'll get yelled at for this. I have both tools, use neither. I will size and chamber, size and chamber the case till bolt closes with very little or no resistance. Lock the die, your ready to resize. Simple.

MOST important is DO NOT over lube cases when sizing, Hopefully you are using Redding FL dies with their carbide sizer button.
 
Warning! This thread is more than 5 years ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.
Top