300BlkTalk

I own both calibers and am familar with the advantages and disadvantages of both, not trying to get into a debate on that.

The 5.56 55gr bullet was originally designed to be fired from a 20 in barrel. When you go to SBR barrel lengths such as a 10 in barrel, you end up with a fireball of unburnt powder and a significant reduction in velocity to which the 55gr round no longer reliably fragments, from a combat standpoint.

Enter the 300 BLK, it is designed to effectively burn its powder in SBR length barrels. Why can't a 5.56 cartridge be loaded with fast burning powders?

I am very experienced with the AR15 platform, but have no experience on reloading. Prior to getting into the 300 BLK cartridges I was not even aware of the different burn rates of powders.

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

didn't cross my mind about pressure and bore size, but now it makes sense!

Thanks!

I'm glad you asked this question, it isn't something I thought of. I just took for granted. I'm somewhat of a beginner handloader, and now I have learned and thought about something new.

I used to load subsonic 80 grain bullets in 5.56. I don't remember the load and even if I did I wouldn't put it here. But there are thousands of subsonic loads using fast powder. I do remember that I didn't use double base powder.

BJK wrote: ↑Mon Dec 20, 2021 1:45 pm I used to load subsonic 80 grain bullets in 5.56. I don't remember the load and even if I did I wouldn't put it here. But there are thousands of subsonic loads using fast powder. I do remember that I didn't use double base powder.

subsonic rounds are a whole different animal.


and as noted, its an easy way to blow up your gun if you goof around