No luck with 1680 for subs

[Mbaker78]

Every sub load I’ve tried for 300aac with 1680 has been dirty, loud, and way slower than desired at around 950fps max. But it cycles flawlessly even at a pretty low charge. Is this pretty typical overall for 1680?

I’ve actually had better luck with IMR4227 for my sub loads, it’s much cleaner and seems to be noticeably quieter through the suppressor.

Ive always heard people talk about how great 1680 is for subs, but I’m not seeing it.

Maybe ill I’ll just try it for full power 6.8spc for my sons undergassed AR. Hopefully it’ll cycle that.

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[Jay Andrew]

1680 has been the go to powder for subs, it’s interesting you are having issues with it.

What are the specs on your rifle? Where is the gas port?

What are your load details?


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[Mbaker78]

The loads I’ve tried are all heavy bullets for caliber 220gr amax, 230gr Lee cast, and 240gr majestic powder coated.

the latest was the 230gr lee cast with charges varying from 9.1 to 10.7 grains. Chrono data below shows a comparison with set 6 being the 240gr majestic with IMR 4227 at somewhere in the neighborhood of 9.5gr

282658A9-206A-48C9-B582-939F30ECBE66.jpeg

The rifle is a 9.5” SBR, ballistic advantage barrel (pistol gas, port opened to 0.100” for improved cycling), standard weight buffer, standard carbine spring, form 1 6” suppressor (baffle type).

I’m mainly just surprised at how dirty and loud it is compared to 4227 though. After going though those 30 rounds (5 groups of 6 shots each) it felt like there was sand all over the bench I was on, which I’m assuming was just unburnt powder. And I had to put my ear pro back on even with the suppressor.

[texascavediver]

Every sub load I’ve tried for 300aac with 1680 has been dirty, loud, and way slower than desired at around 950fps max. But it cycles flawlessly even at a pretty low charge. Is this pretty typical overall for 1680?

I’ve actually had better luck with IMR4227 for my sub loads, it’s much cleaner and seems to be noticeably quieter through the suppressor.

Ive always heard people talk about how great 1680 is for subs, but I’m not seeing it.

Maybe ill I’ll just try it for full power 6.8spc for my sons undergassed AR. Hopefully it’ll cycle that.

1680 works for just about any weight bullet in 300 blk. That's why it's the default go to powder for 300 blk subs. However, its very dirty and not as quiet as other powders. I prefer VV N120 for 300 blk subs. Its much cleaner and quieter than 1680.

[Jay Andrew]

Ok that makes some sense.

The low velocity is due to the shorter barrel. I have to look it up but I believe the SAAMI test barrel is 12 or 14in. So if the date you are using was worked up in a SAAMI barrel the velocity will come in low.

1680 is a slow burning magnum pistol powder,it is so popular in 300blk subs because it produces a lot of gas needed to operate the AR-15 gas system. The beauty of 1680 is you cannot put enough powder in the case to over pressure the round. For a subsonics the targeted velocity is the limit not the pressure.

This is probably one of the few cases where adding more powder will help solve a few things.

1) you’ll get the velocity you want. ~1050fps
2) it’ll raise pressure enough to be closer to the pressure it needs to ignite (low pressure can cause partial ignition and “blow sand” out the end of the barrel)
3) It’ll help clean up the mess as it burns more completely.

Subs are very finicky and only a few powders have the right combination of burn rate and gas production. If you’re finding IMR 4227 is working better for you, then I’d stick with it. 1680 is a US made powder and is typically cheapest which is why it is found in so many factory rounds.


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[Mbaker78]

I just got the dies for 6.8spc, so we’ll see if the 1680 will be gassy enough to cycle my sons rifle (18” rifle length gas, standard buffer and spring) since it doesn’t seem to like factory ammo.