why can't 5.56 be loaded with fast burning powder like 300 BLK?

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airwolf
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why can't 5.56 be loaded with fast burning powder like 300 BLK?

Post by airwolf » Wed Dec 15, 2021 5:44 pm

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.

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20X11
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Re: why can't 5.56 be loaded with fast burning powder like 300 BLK?

Post by 20X11 » Wed Dec 15, 2021 5:57 pm

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

airwolf
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Re: why can't 5.56 be loaded with fast burning powder like 300 BLK?

Post by airwolf » Wed Dec 15, 2021 8:26 pm

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

Thanks!

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Re: why can't 5.56 be loaded with fast burning powder like 300 BLK?

Post by ReadyAimDuck » Wed Dec 15, 2021 9:05 pm

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.

BJK
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Re: why can't 5.56 be loaded with fast burning powder like 300 BLK?

Post by BJK » 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.

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plant.one
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Re: why can't 5.56 be loaded with fast burning powder like 300 BLK?

Post by plant.one » Mon Dec 20, 2021 6:18 pm

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
Reloading info shared is based on experiences w/ my guns. Be safe and work up your loads from published data. Web data may not be accurate/safe.
This disclaimer will self destruct in 10 seconds.

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