cjmac said:
So havent loaded much for auto rifles ... is 3 thousands shoulder bump enough for an AR 15 ?
cjmac
Below is a fired case from my AR15 carbine, I'm loading for three different make AR15 rifles, two are mine and one belongs to my son. Meaning I'm "averaging" the shoulder bump but it varies less than .001 between all three rifles.
Below is the same case after full length resizing and .003 shoulder bump or setback.
Below is a unfired Federal M193 cartridge in the Hornady gauge, meaning my full length resized cases are .002 longer in headspace than factory rounds. And the factory loaded ammunition is over .005 shorter than my chamber, and I'm sizing to make my cases last longer.
Below are some of my .223/5.56 dies, the RCBS black box is a small base die and makes the base of the case .0005 smaller in diameter than the standard green box RCBS die. The big difference between these two dies is the small base dies will size the case further down the case.
Ignore the comment about the shell holder preventing small base dies sizing further down the base of the case by fguffey, small base dies "DO" size further down the case. And if the case needs to be sized around the shell holder area then your loading way over max and need your head examined.
Bottom line, the AR15s military chamber is .002 larger in diameter and has longer headspace settings than a standard SAAMI .223 chamber. I only use my small base die when I purchase once fired or range pickup brass to bring these cases back to minimum SAAMI dimensions. Thereafter I use my standard RCBS full length die and with .003 shoulder bump I have had no problems with this ammunition used in three different AR15 rifles.
NOTE: We live in a plus and minus manufacturing world and your dies and chamber may vary, The small base .223 Redding body die above will make my cases .001 smaller in diameter than my standard RCBS .223 die so nothing is written in stone. Also the brand of case you are using and the hardness in the base web area will affect your sizing methods. Lake City cases are the hardest and .223 Remington and Federal are the softest, and any commercial contract 5.56 cartridges made for the military will comply with military hardness requirements.