300BlkTalk

Reloading 300 Blackout using Siera 220gr subsonic with RX7, 12grains. COL 2.245 as per AR15 load book said COL of 2.260. Once I seat the bullet it will not chamber. Does any one have a suggestion? Brass is pre primered from Detroit Ammo Co.

Where are they hanging up?
Have you put any crimp on these?

improperly sized. Making a dummy round with no powder I'd pull the decap pin and run one through the die, and reseat a bullet. Try that. I always full length size new/primed brass, never trust them to do it. Right.

If I had to guess, it sounds like you are applying crimp with your seating die and deforming the case a little. Try backing the crimp off completely. If that works, buy a Lee FC die and crimp in a separate step.

can you post a pic of some of the ammo in question

Had same problem at first. Play with the crimp adjustment on dummy's till you get it right.
It's very critical of col.
Get a lee factory crimp die and do it in two steps. Not as critical about case legnth.

Man I love my Sheridan Ammo Gauge just for this reason

DragonAzz wrote:Where are they hanging up?
Have you put any crimp on these?

They won't even go in the feed ramp. End of the brass is almost even with the feed ramp. Bolt just hits them but won't move the bulletin at all.

What is the case legnth

And will the gun run with factory ammo?