Rifle: Colt HBAR 5.56 1/7 circa-1994
Brass: Winchester and Lapua
Die: RCBS full length with Lyman carbide expander
Press: Dillon 1050
Lube: RCBS Case Slick
Measuring tool: RCBS Precision Mic
For years, I've loaded for my .223 AR with the usual method of setting back the shoulder by about .003 from the fired case, as measured with my RCBS Precision Mic tool. I've never had a feed malfunction, nor was I ever unable to easily eject an unfired cartridge.
Recently, I experimented with chambering dummy cartridges made with cases that were deliberately not resized enough. To my surprise, the cases of the dummy cartridges came out with shoulders pushed back quite a bit more than I normally set them back while resizing. Here are the measurements using the RCBS Precision Mic tool:
Fired picked up cases read 0 or -1 on the tool
My "as-usual" resized cases are mostly -3 or -4 after exiting the resizing die
Experimental dummy cartridge case, not resized down enough reads -1
Same case after chambering from magazine and dropping the AR bolt on it is now -7 !!!
What's going on? Have I been setting back my case shoulders insufficiently all these years, and having the rifle do the rest of the job by press-fitting the cartridges to the chamber?
Should I stick with my tried and true shoulder set-back numbers or should I readjust my resizing die to push the shoulders back a few thousands from this -7 reading of press-fit dummy cartridge cases? If I readjust the die, it would be a huge change from how far I normally push back the case shoulders.
Brass: Winchester and Lapua
Die: RCBS full length with Lyman carbide expander
Press: Dillon 1050
Lube: RCBS Case Slick
Measuring tool: RCBS Precision Mic
For years, I've loaded for my .223 AR with the usual method of setting back the shoulder by about .003 from the fired case, as measured with my RCBS Precision Mic tool. I've never had a feed malfunction, nor was I ever unable to easily eject an unfired cartridge.
Recently, I experimented with chambering dummy cartridges made with cases that were deliberately not resized enough. To my surprise, the cases of the dummy cartridges came out with shoulders pushed back quite a bit more than I normally set them back while resizing. Here are the measurements using the RCBS Precision Mic tool:
Fired picked up cases read 0 or -1 on the tool
My "as-usual" resized cases are mostly -3 or -4 after exiting the resizing die
Experimental dummy cartridge case, not resized down enough reads -1
Same case after chambering from magazine and dropping the AR bolt on it is now -7 !!!
What's going on? Have I been setting back my case shoulders insufficiently all these years, and having the rifle do the rest of the job by press-fitting the cartridges to the chamber?
Should I stick with my tried and true shoulder set-back numbers or should I readjust my resizing die to push the shoulders back a few thousands from this -7 reading of press-fit dummy cartridge cases? If I readjust the die, it would be a huge change from how far I normally push back the case shoulders.