Help needed on a 300BLK reload

[dellet]

Neck diameter is .339 to .340.

That’s your problem. Chamber is only .335-336

viewtopic.php?f=141&t=88599

[maxg]

So that means my sizer die isn't working correctly? What could cause that? Thank you for your help.

[maxg]

... or I'm using bad brass.

[dellet]

... or I'm using bad brass.

Check the thickness. No more than .013” and that pushing it.

.308+.013+.013= .334” that’s max and in a minimum chamber of .335 will likely show pressure signs early.

[BobinNC]

Neck diameter is .339 to .340.

I'll also say that's your problem. My 110 Grain Hornady's or 110 grain Nosler loaded neck diameter is .330". That's in Starline 300 Blackout Brass, not cut down 223.

[MaxG66]

Wow. I see. The chubby round never had a chance.

I've got some more reading to do, and a lot of measuring of my inventory. I'm surprised I haven't run into this before now.

Thanks all for the help!!!

[rebel]

What brand brass is that .339?

[BJK]

Sounds like you might need to turn some necks. It's not a big deal.

[dellet]

Considering a thread going on in another forum,....
I’ll put on my safety nazi hat

Max needs to throw those headstamps in the garbage and do some reading.

Most manuals will have version of the below drawing, simply looking at that would have given the answer. His potential problems don’t stop there. Because the brass is so much thicker, case capacity will me greatly reduced and pressure increased. Sounds like he’s using mixed headstamps, so a safe load in one case could be dangerous in the next.

Book pressures are measured with a certain amount of neck clearance. 300 BLK brass with a loaded neck diameter of .330” or less will created a lot less pressure than something that barely slips into the chamber at .3349”. Might even crimp the bullet to a point and raise pressure even more.

Then there is the question of load data and charge weight. This has come up before with Hodgdon data and Lil’gun. Their starting load of 13.6 grains with a 180 grain bullet is everyone else’s max. A few people tested their data when they changed it a few years ago, not to many were able to reach the published max loads without getting severe pressure signs.

Lots of little things can combine and ruin a perfectly good range trip, just some food for thought.

[20X11]

So, the round wouldn't fully chamber, the bolt wasn't rotated in place and the "design" prevented the firing pin from striking the primer. That is good because you don't want the round going off on an open bolt.