What's the point of a 20" barrel anymore?
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Darrell
- Posts: 6586
- Joined: Mon Aug 18, 2008 11:12 pm
Re: What's the point of a 20" barrel anymore?
A guy at the range last weekend told me he wants a 24" 1 in 12" barrel, for shooting 40 gr loads at prairie dogs. Do they even make such slow twists anymore?
Eppur si muove--Galileo
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Whirlibird
- Posts: 1181
- Joined: Tue Aug 19, 2008 11:58 pm
Re: What's the point of a 20" barrel anymore?
Krieger will happily make one.Darrell wrote:A guy at the range last weekend told me he wants a 24" 1 in 12" barrel, for shooting 40 gr loads at prairie dogs. Do they even make such slow twists anymore?
https://www.kriegerbarrels.com/twist#ar15
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D5CAV
- Posts: 2428
- Joined: Tue Aug 19, 2008 2:48 am
Re: What's the point of a 20" barrel anymore?
It depends on what SAAMI Spec, factory loaded ammo you plan to use.
Not much point in a 20" barrel for 9mm Luger. The powder stopped burning at about 4".
With 50 BMG, you'll have a 12" flame coming out of your 20" barrel, so not much point in a 20" barrel for that, either.
With 7.62 NATO, the powder is still burning at almost 18", so I like 21" barrel on my standard M14s and my Winchester Model 70s have 24" barrels.
With 5.56 NATO, the powder is still burning at 15", which is why the "Shorty" M16s (the predecessor of the M4) had those long flash hiders. I like bayonets and a bayonet doesn't fit on a "M4 Style" barrel, because it's 16" legal length,so the bayonet rattles around 2" down the barrel. A true M4 barrel (14.5") requires an SBR tax stamp.
In addition, as was stated by others, you actually pick up a few fps of velocity after the powder has stopped burning. There is a point of diminishing returns, and that point is about 28" with a 7.62 NATO and about 26" with 5.56 NATO, where the friction in the barrel actually starts to slow down the bullet. There is a reason that the cartridges were designed with the charge, pressure and velocities they have - they were designed for 20" barrels.
I haven't SBR any rifles, but I have a couple of 5.56 NATO chambered pistols I bought as toys. They really are toys. I can see no practical use for them. They are loud flamethrowers. We put one on a chronograph, and the velocity out of a 10" barrel was under 2500 fps, and the flash was over 6" out the front.
If it was me, and I really felt a need for a 10" 5.56 NATO launcher, I'd load my own ammo with a powder charge that got me 2500 fps or better and burned all the powder in 10" (essentially designing my own wildcat cartridge optimized for a 10" barrel), but I don't have the time to mess with that.
Not much point in a 20" barrel for 9mm Luger. The powder stopped burning at about 4".
With 50 BMG, you'll have a 12" flame coming out of your 20" barrel, so not much point in a 20" barrel for that, either.
With 7.62 NATO, the powder is still burning at almost 18", so I like 21" barrel on my standard M14s and my Winchester Model 70s have 24" barrels.
With 5.56 NATO, the powder is still burning at 15", which is why the "Shorty" M16s (the predecessor of the M4) had those long flash hiders. I like bayonets and a bayonet doesn't fit on a "M4 Style" barrel, because it's 16" legal length,so the bayonet rattles around 2" down the barrel. A true M4 barrel (14.5") requires an SBR tax stamp.
In addition, as was stated by others, you actually pick up a few fps of velocity after the powder has stopped burning. There is a point of diminishing returns, and that point is about 28" with a 7.62 NATO and about 26" with 5.56 NATO, where the friction in the barrel actually starts to slow down the bullet. There is a reason that the cartridges were designed with the charge, pressure and velocities they have - they were designed for 20" barrels.
I haven't SBR any rifles, but I have a couple of 5.56 NATO chambered pistols I bought as toys. They really are toys. I can see no practical use for them. They are loud flamethrowers. We put one on a chronograph, and the velocity out of a 10" barrel was under 2500 fps, and the flash was over 6" out the front.
If it was me, and I really felt a need for a 10" 5.56 NATO launcher, I'd load my own ammo with a powder charge that got me 2500 fps or better and burned all the powder in 10" (essentially designing my own wildcat cartridge optimized for a 10" barrel), but I don't have the time to mess with that.
“None are more hopelessly enslaved than those who falsely believe they are free.” Johann Wolfgang von Goethe