300 AAC Blackout Case Head Sizing Problem

[jmorris]

I love the idea of roll sizing back to factory spec.

I don't love the $900 price tag....

Try this then.

https://www.midwayusa.com/product/1012847155

[popper]

Small bae die sizes lower on the case and a smidgen smaller. If you reloaded and shot those cases in your gun, without problem, continue. You may have a larger chamber so they won't fit in SAAMI gauge. Range PU of BO or 223 may be from another larger chamber gun. Chamber the large cases in your gun and see if the bolt closes. Note also. Over pressure loads expand the case by the head first. I got one that looks like a belted magnum due to an over pressure load. Had to prey the bolt open.

[ulav8r]

well there is probably your problem.
I do not shoot the 300AAC BUT DO SHOOT .223REM and have done so for years using a sack of milserp brass I was given...if I sort headstamps there is 4 different types,one of which has always given me trouble so it gets chucked out..I BELIEVE this was possibly a hotter tracer or heavier load ,powder charge ,projectile weight or both.... so the case got a jolly good whoomph on its one use and hasnt shrunk back as small as it should.... if you think about it,how can that rim be wider unless it was to begin with,EG was manufactured bigger to begin with...the only possible way it,the rim.could grow outwards would be brass flow....and when do you get brass flowing that way,that much????? the issue I had was case jamming in LEE auto prime,oh man did that do my head in,remove tray of primers,making sure to clear the on ramp,try forcing primer in deeper and then try to get case out,some would stick in shell holder on press too,it was like the rim itself was out of shape/off square or too thick.
in the .308 the only brass we have ever had issues with was S&B it was just too hard and felt like press handle was going to tear off.
chuck a micrometer on a not fitting case and see whats going on....
but you over thinking it,if it fits in rifle n fires..where is the problem again????

The problem is he wants to use a case gage to check for proper sizing because the barrel does not facilitate easy plunk testing. His solution of checking the rims before conversion to 300-AAC is his best no extra cost solution.

[Liberty1776]

well there is probably your problem.
the issue I had was case jamming in LEE auto prime, oh man did that do my head in, remove tray of primers, making sure to clear the on ramp, try forcing primer in deeper and then try to get case out, some would stick in shell holder on press too, it was like the rim itself was out of shape/off square or too thick.

I run into that problem with my Dillon shellplate, too. Most brass slides in and out just fine. Every once in a while one piece is persnickety and sticks. It's a mystery.

[Omega]

I convert 99% of my 300BLK, and 277WLV brass from LC brass and never had this issue, it may just be a combination of dings on the rim and gauge variation. Since I form my brass, I bought a Sheridan slotted gauge to see exactly where my sizer was having issues, and at first I had a few. Turned out that my Lee case holder was a bit tall, I took a bit off it and worked, but RCBS case holder worked right off (wish I tried that first). Though I figured out the issue using Lee dies, the Hornady, and RCBS didn't have this issue. One thing I noticed on the LC brass was that cases fired through the SAW were harder to size, and the extractor dinged the rim more, so it may be cases like that that are giving you issues.
These are 277WLV but they look the same.

[gwpercle]

Rims too large ... pick up an Acme Rim Trimmer ... trims them pesky oversized rims back to where they fit the case gauge .
Gary