Dillon 308 die question ? using a headspace gauge ?

[243winxb]

Post #21 should read CARTRIDGE in stead of chamber

Use a "CARTRIDGE" headspace gauge to set up the sizing die for bottle neck type cases or better still, use a RCBS Precision Mic or Hornady Comparitor. (The edit button is missing.)

 

[Welding Rod]

+1 Here's how it works. You fire a factory round or a handload you made on new-unfired brass. Then you put that round (s) in the case gauge. it will tell you, in .001 accuracy, exactly what your chamber has for headspace. It tells you where your case shoulder is. Example, my .223 bushy, leaves the cases + .007 longer than minimum headspace for .223.

I would think you could do it either way, but for me i perfer the RCBS Precision Mic as i can see exactly what i am doing...

I know this is an old thread but I am replying as I see this practice as unsafe.

When brass is extracted from an auto loader its post-fired headspace length can be longer than the chamber dimension. I would never use this dimension as a reference for setting sizing dies for an auto loader as the headspace dimension on your reloads could then be too long.

My M1A's brass measures quite a bit longer than the measured headspace dimension of the chamber (using a RCBS Precision Mic to compare the lengths of both the headspace gauge and the fired brass).

The way to measure headspace is with a set of headspace gauges.

 

[Jdillon]

I use several different tools to set up my FL sizing dies including; Hornady, Innovative Technologies, RCBS Precision Mic as well as Wilson and Dillon case gauges. For my gas guns, I found the RCBS Precision Mic works best on fired cases due to irregularities in the shoulder of fired cases. I setup my Dillon 550B with the RCBS Mic to achieve a "bump" of approximately .003" on .223 cases. I run a number of test cases (10-12) through the sizing die after final adjustment to verify consistent sizing. Although somewhat time consuming, it takes the guess work out of setting up your dies.

Case gauges are fine but but will not give you the same level of precision as using the other tools mentioned. On bolt or single shot rifles, the IT, Hornady and RCBS all work very well.

 

[Walkalong]

I use a case gauge like Slamfire1 showed to check cases sized for autos. I use other methods to size for a gun when I do not expect to fire it in any but my gun. If you use a case gauge for that as well, it will ensure proper headspace in any gun with a properly installed barrel with a properly machined chamber. It eliminates measurement errors as well. Stick the case in and look at it. Very simple.