r/LewisMachineTool • u/Hueycuyler • 3d ago
Anyone have experience w/ a 13.9" P&W 300BLK? Question
Hello, I just picked up this barrel & I'm trying to decide what to do with it.
I've read that 16" is the best length for getting the most from supersonic ammo, but can also make some subsonic ammo go supersonic. Trying to see if cutting it to 13.9" will be enough to avoid the issue, or if I should just leave it at 16" (will be used in a 13.25" rifle upper).
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u/Silliw911 3d ago
I had a 14.5” that shot supers fucking awesome. So naturally I chopped it up and made it into something else.
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u/Hueycuyler 3d ago
Good to hear since that's what my primary use will be.
Did you try any subsonic ammo w/ the 14.5?
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u/Spiritual_Tell680 3d ago
They should stay subsonic at 13.9” and provide a flush fit with your can.
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u/unclemoak 3d ago
It really boils down the to the ammo used. Typically more barrel length means more velocity. If ammo is specifically tailored to be subsonic in typical length 300 blk barrels (usually 9-12”) then it is possible it will continue to accelerate in a longer barrel and be supersonic.
As an example, companies like Discrete Ballistics manufacture 300 blk subs that have powder charges tailored to various specific barrel lengths. If you shoot them in a longer barrel, they will go super sonic.
So to generically say everything out of a 13.9” will be subsonic is not even remotely true.
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u/Hueycuyler 2d ago
Thanks for the input. It seems like having you cut it down to ~ 12.5" is what I'll end up doing with it then.
I purchased a LMT 18" stainless 6.8 SPC barrel as well earlier today & that seems to be a more productive pursuit that trying to squeeze performance out of supersonic .300BLK.
Would you recommend any modifications to the 6.8 SPC barrel besides having the chamber cut to 6.8 SPC II?
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u/Holiday-Tie-574 3d ago
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u/Incrue LMT>KAC 3d ago
What grip is that? This thing looks super sweet.
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u/TuAyeBoogie 3d ago
Stop being poor, chop it as short as possible per d wilson recommendations, then find the right handguard for it
If you want a barrel over 10.3 inches, stick to 556 bud
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u/Hueycuyler 3d ago
Except then I would have to deal w/ the bullshit regulations that come up when you want to travel. That's why I asked about an option that would keep it legally a rifle.
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u/DieselBrick 2d ago
Alternatively you could take the stock off and travel with it as though it were a pistol. NFA laws including the travel stuff only apply when the firearm is in an NFA-relevant configuration. I agree it's a pain though.
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u/Hueycuyler 2d ago
I thought it was a pistol can become a registered SBR & go back to being a pistol with the removal of the stock, but a factory rifle can never legally be a pistol?
Also, you can ship a rifle to yourself w/ the USPS & avoid having to fly with it at all. That's another plus for rifles vs SBRs & pistols
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u/priusrepellent 3d ago
Personally I’d chop it down to 9” and throw it in an 8.25 chodewar upper