300 blkout 1/5 barrel twist

Discussion about rifles in 300 AAC BLACKOUT (7.62x35mm), hosted by the creator of the cartridge.

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dieselherb
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300 blkout 1/5 barrel twist

Post by dieselherb »

Anyone try the 1/5 barrel twist?
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dellet
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Re: 300 blkout 1/5 barrel twist

Post by dellet »

I have had one for a few years, do you have specific questions?

Great for subs, some problems with supers, length and velocity are limiting factors.
300 Blackout, not just for sub-sonics.
dieselherb
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Re: 300 blkout 1/5 barrel twist

Post by dieselherb »

I have heard the twist rate is hard on bullets not solid(copper) ? The 8.6blkout has the same issue. Do you load yourself? I have since I first bought the 300 blkout.
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dellet
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Re: 300 blkout 1/5 barrel twist

Post by dellet »

dieselherb wrote: Fri Mar 08, 2024 5:00 pm I have heard the twist rate is hard on bullets not solid(copper) ? The 8.6blkout has the same issue. Do you load yourself? I have since I first bought the 300 blkout.
The spin can be hard on a lot of bullets, even the solids that are designed for rapid expansion or fracturing. The key is to keep velocity under 2100 fps, unless the bullet is rated for a spin over 300,000 rpm.

A good example would be the Lehigh 194 ME bullets. They open in flight in a 1/7 around 1400 fps. That’s 144,000 rpm. A 1/5 twist hits that rpm at 1000 fps.

I shoot a lot of the 110 Varmageddon, about 2300 fps. or 330,000 rpm. A good clean barrel, slow rate of fire and it’s not a problem. Start shooting 3-4 rounds a minute and the barrel heats up causing the bullets to explode in flight. Takes about 20 rounds on a warm day.

You just really need to know the limits of your bullet choice and no matter what you’re told, test it yourself.

The problem is that the 1/5 twist was more or less designed for a short barrel, 5-5.5”. At that length it’s hard to get velocity up over 2100 fps. In an 8” barrel it’s no problem. But even with subs at 1000 fps, some bullets just won’t work.

Loading your own really is the best thing to do.
300 Blackout, not just for sub-sonics.
dieselherb
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Re: 300 blkout 1/5 barrel twist

Post by dieselherb »

I've on the Discord 8.6blkout forum. They've been saying the same about the 8.6 but most of them use suppressors. And warn some bullets will destroy the can. I don't have one so I can experiment close range on paper to see if they hold together. Most of them don't shoot Supers.
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dellet
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Re: 300 blkout 1/5 barrel twist

Post by dellet »

dieselherb wrote: Mon Mar 11, 2024 7:13 pm I've on the Discord 8.6blkout forum. They've been saying the same about the 8.6 but most of them use suppressors. And warn some bullets will destroy the can. I don't have one so I can experiment close range on paper to see if they hold together. Most of them don't shoot Supers.
I forgot to include this this morning, formula for spin rate if you don’t have it

12/twist x 60 x velocity = spin rate

12/3 x 60 x 1050 = 252,000

A lot of match bullets start failing around 240,000

1300 fps in a 1/3 is 312,000.

Look at the Maker bullets, if he has one for the 8.6, I would absolutely trust it.
I’m sure he does.
300 Blackout, not just for sub-sonics.
dieselherb
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Re: 300 blkout 1/5 barrel twist

Post by dieselherb »

I received some Maker 350 gr for the 8.6 yesterday. Will use those for hunting. I saw a pic of one expand in gel, amazing. I have some 160gr copper for Supersonic and 285gr for subsonic, but both are expensive for plinking
dieselherb
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Re: 300 blkout 1/5 barrel twist

Post by dieselherb »

Is there a video of the 300blkout 1/5 shooting into ballistic gel?
dieselherb
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Re: 300 blkout 1/5 barrel twist

Post by dieselherb »

I bought some Barnes 150gr MPG bullets. They say lead free, can I run them super in the 1/5 barrel. 308s
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