.300 BLK routinely loaded with pistol powder?

I saw a video that stated that .300 Blk round are routinely loaded with pistol powder. I took this to mean supersonic loads included. It stated that the powder was completely burned in the first 9" of barrel, so longer barrels are irrelevant, at least from a velocity standpoint. Is this true?

If so, why bother getting a full length (16") barrel AR? On the flip side, does any major company load .300 BLK with rifle powder specifically for longer barreled guns?

And does this make it a better round for shorter barreled ARs?

Welcome to the topic of interior ballistics — it is complex.

Powder burns, not explodes, that is characterized on a pressure vs time graph. Fast (pistol) powders have short rise times, and quick pressure decay. Slow (rifle) powders have slower pressure rise and decay. If you look at the area under the curve as representing equal power (a simplification), a pistol powder will have a fast peak pressure, and a higher peak pressure to equal the area under the curve of a slower rifle powder.

The shape of the case and the ratio of case volume to bore diameter (piston area) also matter. A 9mm pistol case will uncork and drive the bullet down the barrel much more easily than a .243 Winchester case where you have to drive 10-15 times as much powder through a smaller (6mm vs 9mm) bore. The 6mm bullet, 105gr for example, also has a longer bearing surface than a 115gr 9mm pistol bullet, and is more difficult to force down the barrel.

So the 300Blk is a tweener. With 300Blk, you can load it with a slow pistol powder or a fast rifle powder. More case to bore than a 9mm, less than a 308Win. Slow pistol powders like H110 and 2400 work well with light bullets and short barrels. Heavy bullets benefit from longer barrels and slower powders, to allow all the propellant to combust before the barrel uncorks when the bullet exits the muzzle. Some powders like AA1680 and CFE-BLK work well with both weights.

If you want to shoot light 110gr bullets in a short 8-10” barrel, try H110 or 2400. Data listed here: https://load-data.nosler.com/load-da...-aac-blackout/

To address your other questions:

If so, why bother getting a full length (16") barrel AR? I have both 16” and 8” barrel 300Blk. They both shoot well, but one is a lot handier, especially with a can. And if you shoot 300Blk, you are going to want to suppress it. Trust me. It is fun.

On the flip side, does any major company load .300 BLK with rifle powder specifically for longer barreled guns? Unknown. I hand load all my ammunition.

And does this make it a better round for shorter barreled ARs? In my opinion, yes. 77gr 556 ammo out of a 10.5” barrel AR is really obnoxious. Loud. Antisocial. Even with a can. And I think the 110 VMax is a better short-barrel bullet in this scenario than The 556 of any weight. 220gr subsonics shot with a can are quite fun, and usually draw a crowd at the shooting range wondering what you are shooting that is quiet. 220gr do not expand well at 1000 fps, but Hornady does make a 190 plastic-tipped sub to address that need. .

My thoughts, TriggerF-16’s much better written words.

My fun handload for the 7.5” 300BLK pistol is 18gr H110 and 125FMJ.

https://uploads.tapatalk-cdn.com/202...3419a315e4.jpg

@Triggerf16 said it all.


I will add this - .300BO is specifically designed for that niche of fitting in a short barrel AR15 based weapon system and magazine, while being very easy to effectively suppress. The slowly but relentlessly growing support and flexibility of the cartridge is testament to other discovered 'sweet spots' available such as the supersonic loads with the Barnes 110gr bullet. So applying conventional 'rifle' thinking to .300BO loads is a great way to talk yourself out of buying one, because a myriad of other intermediate 7.62/.30 cal cartridges exist that can do it all with rifle powders from NFA-legal rifle length barrels.

Every factory AR I've seen in .300BLK uses a super short pistol-length gas system even if it's got a 16in barrel, too, which tells me that the loads that work all use fast powders. From a cartridge efficiency standpoint the .300BO is fantastic because the nearly straight wall case combined with a relatively small capacity with a relatively wide bullet base means it can get all that 'stuff' done well with a fast powder, without any issues or drama for all the additional reasons already mentioned.

I strongly suspect that if one started handloading with slower rifle powders in the hopes of getting more out of a 16in barrel, they'd deal with other function/cycling issues related to the gas system length in a typical .300BO AR. If we're being honest, the NFA is really the only reason that any barrel longer than about 12in exists for a .300BO.

A few things come to mind:

Because of the case capacity and bullet size, you cannot cram enough of the slower-burning rifle powders into a .300BO case to make a difference.

Ex: I'm currently running Shooter's World SBR-SOCOM for my supersonic loads from my Rattler. I am running a pretty damn close to max load of ~20.5gr (max is 22gr) and that charge is every so slightly compressed when I seat a 125-grain TNT over it. SOCOM is a very nice, uniform, ball powder, and it will pack into a case much better than any rod-type powder. It's one of the smallest 'rifle' powders out there; in that it has a burn rate very similar to VV N120 and IMR 4198. Yet, I can pack nearly 2 more grains of SOCOM into a .300BO case than I can N120, due to the shape of the powder.

The reality is - 20-22gr is the maximum amount of powder you can cram into these little cases.

By contrast, VV lists the beginning charge of N130 (the next slowest after N120) for .308 with a 125-grain bullet at 37gr, to produce a paltry 2684fps.

Remember too, that slower burning powders require MORE pressure to burn. And the .300BO has a fairly low pressure max for a centerfire rifle cartridge (55k psi per SAAMI vs. 62k for .308 WIN). So you run the risk of running into pressure issues quickly with a slower burning rifle powder in .300BO. N120/SOCOM/H110 can already get you up to 50-53k without working very hard. I could probably cram 23gr of SOCOM under a 125-grain TNT and compress is and create a 60k proof load without an issue.

Guys, lots of useful information in here. Thanks.

Quote:

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Originally Posted by JRB

[If we're being honest, the NFA is really the only reason that any barrel longer than about 12in exists for a 300BO.

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I agree.

Pic of the current situation. Work In Progress: Step 1

https://uploads.tapatalk-cdn.com/202...3cb0856983.jpg

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I see a lot of brass trimming in your future