So I quickly found my Ruger AR556 MPR doesn't play well with my reloads. Plenty (too many!) failures to fully chamber and extract the fired cases on that rounds that did chamber, like 1 in 4 or 5 or so. Functioned 100% with factory brass and steel cased ammo. When it fired, my loads seemed nicely accurate. No case mouth or shoulder bulges to interfere with chambering.
So I get out my micrometer and SAAMI .223 specs and find that my Lee sizing die is sizing at or near SAAMI max spec, with a few cases being around .0005 or so over max. Yes the sizing die was tight against the shell holder. As best I could figure from measuring cases fired in the MPR, its chamber is at or near SAAMI minimum specs (fired cases in the body and case head (aka web) would be smaller than what my sizing die was sizing by 1-2 thousands). Measuring factory loads, the cases were 3-4 thousands smaller than SAAMI max specs...no wonder they chambered fine.
Looking through my stuff, I found 2 more Lee sizing dies (included when I'd buy somebody's whole reloading set up, mainly going for the powder, cases, bullets, primers and other equipment). Found 1 Lee die sized brass exactly like the Lee die I'd been using for years. Found the other extra Lee sizer would size the case head and about 1/3rd up the case body .001" more than the other 2 dies. Immediately set that tighter die up to use for regular use, but did not try it in the Ruger, as my RCBS small base die arrived shortly thereafter.
The SB die would size brass cases .001" smaller at the case head and body than the "tight" Lee die. On steel cases it reduced the body part by .001", but did not seem to reduce the case head (web) any smaller than the tight Lee die (springback?). Ran a quick small test of 27 brass cases and 2 steel cases reloaded after running through the SB die. All chambered, fired, and extracted with no problems. I need to do more testing before loading a quantity of ammo for the Ruger MPR, but even if they don't function in the Ruger, I know they'll do fine in my other more generous chambered AR bbls. For now, I'm shooting factory steel in the MPR, as I now have a good use for it. I am contemplating just using the SB die for all my .223/5.56 reloading.
So I get out my micrometer and SAAMI .223 specs and find that my Lee sizing die is sizing at or near SAAMI max spec, with a few cases being around .0005 or so over max. Yes the sizing die was tight against the shell holder. As best I could figure from measuring cases fired in the MPR, its chamber is at or near SAAMI minimum specs (fired cases in the body and case head (aka web) would be smaller than what my sizing die was sizing by 1-2 thousands). Measuring factory loads, the cases were 3-4 thousands smaller than SAAMI max specs...no wonder they chambered fine.
Looking through my stuff, I found 2 more Lee sizing dies (included when I'd buy somebody's whole reloading set up, mainly going for the powder, cases, bullets, primers and other equipment). Found 1 Lee die sized brass exactly like the Lee die I'd been using for years. Found the other extra Lee sizer would size the case head and about 1/3rd up the case body .001" more than the other 2 dies. Immediately set that tighter die up to use for regular use, but did not try it in the Ruger, as my RCBS small base die arrived shortly thereafter.
The SB die would size brass cases .001" smaller at the case head and body than the "tight" Lee die. On steel cases it reduced the body part by .001", but did not seem to reduce the case head (web) any smaller than the tight Lee die (springback?). Ran a quick small test of 27 brass cases and 2 steel cases reloaded after running through the SB die. All chambered, fired, and extracted with no problems. I need to do more testing before loading a quantity of ammo for the Ruger MPR, but even if they don't function in the Ruger, I know they'll do fine in my other more generous chambered AR bbls. For now, I'm shooting factory steel in the MPR, as I now have a good use for it. I am contemplating just using the SB die for all my .223/5.56 reloading.