full length re-sizing verses neck sizing

[stevesmith]

You need the headspace (bump) gauge and comparator to measure your fired cases in order to know what actual dimension you want to push the shoulder back .001" or .002" FROM. Look up "headspace gauges" on a site like Sinclair International or some similar shooter's supply outfit. You will need the insert which matches the shoulder angle for your caliber (in your reloading data manuals the case dimensions should be given) and install the comparator with insert on one blade of your caliper. Measure about 10 fired cases (after a thorough cleaning) and use the average. Run these cases through your resizing die set up to factory specs (per the manual or my description above) and measure them again. Compare the two average headspace measurements. If the fired cases are (I am making up numbers, I don't have data for 338LM anyone out there who does please throw some real numbers our way) 3.555" and the resized cases are 3.553", then you are in good shape. If the resized cases are shorter than 3.553", then you might benefit from adjusting the dies/or using comp shellholders as previously described.

so basically measure 10 fired casings get a average...or measure one then resize it and see if it set it back .001-.003 and if its more then i need the spacers and if not enough i can adjust the die??
im admitting pure stupidity here on this..just trying to learn something.
thanks for any and all of your input and help..

Steve Smith

 

[7magcreedmoor]

First make sure you are running a tight press before you do any measuring. If the resized cases are slightly shorter than the fired ones, adjusting the die can tune that. If significantly longer, you've got a bad die set or a bad chamber. Doubtful the latter will be the issue, or you'd likely not be able to chamber the factory ammo without considerable force on the bolt handle.

 

[Bill Johnson]

so basically measure 10 fired casings get a average...or measure one then resize it and see if it set it back .001-.003 and if its more then i need the spacers and if not enough i can adjust the die??
im admitting pure stupidity here on this..just trying to learn something.
thanks for any and all of your input and help..

Steve Smith

It really doesn't matter how your fired cartridges compare to a headspace gage. You can't neck size forever anyway. Eventually you have to full length resize. So what you want to know is where to set up your dies to bump the shoulder back .002 from it's fired condition. This is relatively simple and inexpensive to do. Your cartridge's datum is where the shoulder measures about .458"

Using a 7/16 ID bushing with a slight bevel as pictured below, you take a reading on your 10 cartridges, average, then compare to a case full length resized. The differential reading between the 2 is how much you are bumping the shoulder back full length resizing, setting up the die per the die instructions. The bushing pictured came from Home Depot and cost $4. I have a 3/8 bushing for 30-06 and 308. You do not have to hit right on the datum. As long as you are somewhere around midpoint of the shoulder, your differential reading will tell you what you need to know.

Hypothetically, if you are setting the shoulder back .012, you want to raise the die .010 to get the .002 bump. You can do that by adjusting the die (put a .010 feeler gage on top of the shellholder and set the die per instructions) or you can use the die shims I mentioned previously or the different shellholders others have mentioned.

This is old-school stuff that's been around a long time before they came out with the fancy and expensive comparative tools available now.