300BlkTalk

By "barrel tube", do you mean the chamber, or the upper receiver where the BCG rides?

Photos can be posted by using a Photo hosting site and pasting the link in your post.

Call Dillon Customer Service?

So, I also need to ask what your trim length is after sizing?

Generally speaking, yes small base (SB) dies were designed to handle this. Mixed headstamp may include 5.56 bra6s that was fired from a machine gun (notorious for having this base issue), then chopped down and sized for 300blk. Or you can buy a roll sizer...or buy brass from HOSER or have Hoser proc...

They'll be fine. That said, the only primers I've EVER heard of slam fire with are Rem 6 1/2...the manufacturer specifically warns against using these.

You'll be hard pressed to find a better supersonic powder for 300blk than 300MP.
It's clean, meters well, very consistent and predictable throughout the load range, and is temperature stable.

Look for user name Hoser. THE BEST!

A. shoulder angle and depth.
B. Cartridge volume/diameter vs Bore Diameter

Fast burning powders in a high capacity for Bore diameter case will build pressure too fast and create an outright explosion rather than the controlled explosion propelling the bullet down the bore

Here is a link to another discussion on TNT 125s
viewtopic.php?f=141&t=109064

Well, some powders (H110 for example) can experience "flashover" on low volumes in a case. Google it if you need to, but it can result in SERIOUS over-pressure conditions.
Google - low powder charge detonation