Initial loading issues

[jinx44]

I assembled an AR in .300 whisper with parts from a local dealer. I believe the barrel is a J&T. My dies finally came in yesterday and I started to load some rounds last night but encountered problems.

Dies are Redding FL (adjusted down to touch the shellholder), brass is .223 factory remington, case length trimmed to 1.355", bullets are 220MKs.

I started by loading the OAL so they would fit in a standard metal LE mag. Then I tried to chamber one and the bolt wouldn't close. I shortened the OAL, and after several tries, it finally chambered. I fired this round and it was super-sonic at 9.7gr of AA#9. The case didn't eject. It was easily pulled by manually ejecting the case. I am sure I felt the action cycle, and there seems to be a mark on the case head from the ejector trying to pull it out of the chamber.

I then took a sized case and cut 4 slits in the neck and inserted a bullet so I could find where it touched the lands (read about this trick on a 300 whisper page that was linked from this site). This case wouldn't chamber either. The bullet was loose enough in the case that it should have easily pushed back if needed. So then I tried to chamber a freshly sized, empty case and the bolt still wouldn't close. It required considerable force to get the bolt to close. When I extracted this case, there were marks on the shoulder where it seems the chamber was pushing back on the shoulder.

I compared this case, a loaded case, and the fired case. The neck on the fired case is MUCH longer than the neck on a sized case. .265" on the fired, .221 on the sized. The shoulder also appears to be pushed downward, but is extremely hard to measure because the shoulder of a sized case is not very pronounced.

Obviously, either my chamber is too short, or the dies are loading the case too long. It seems my reloading manuals disagree on dimensions. Where can I find the correct SAAMI specs?

Also, sized case neck OD is .333", loaded case is .334", and fired is .336". Is that correct or a little tight?