Ar barrel twist vs bullet gr.
- Thread starter hotguns
- Start date
Basically, the heavier the bullet you want to use, the faster the twist you'll want. The old standard 1:12" twist rate on the original M-16 & civilian Colt AR-15 SP1, etc...was fast enough to stabilize bullets up to about 60 grs. Some shot the heavier bullets okay, some not so much. I've found that mine seems to really excel with bullets in the 50-55gr range, but it will work okay with bullets as light as 40 grs.
Current M-16s & M4s have a 1:7" twist rate so as to stablize the heavier bullets the military now uses in the 62-69 gr range. Target shooters have successfully used bullets as heavy as 77-80+ grains with the same twist, however, the latter required you single load them.
In between is the 1:9 & 1:8" twist rates. They can generally be counted on to shoot pretty much everything okay, with perhaps the exception of the very lightest and very heaviest bullets.
You have to bear in mind that every barrel is different, so it isn't unusual to find a barrel that will shoot a bullet weight well that the twist rates says it shouldn't even stabalize properly.
As to what twist rate is best for you, it all depends on what you want to shoot. Since you mentioned a target style AR, I'm guessing you're looking at shooting heavier bullets? In that case you'll probably be best served with a fast twist rate, such as 1:8" or 1:7" In a lot of cases, guys in this situation first decide on what bullet they'll be shooting and then choose the twist rate to match!
Current M-16s & M4s have a 1:7" twist rate so as to stablize the heavier bullets the military now uses in the 62-69 gr range. Target shooters have successfully used bullets as heavy as 77-80+ grains with the same twist, however, the latter required you single load them.
In between is the 1:9 & 1:8" twist rates. They can generally be counted on to shoot pretty much everything okay, with perhaps the exception of the very lightest and very heaviest bullets.
You have to bear in mind that every barrel is different, so it isn't unusual to find a barrel that will shoot a bullet weight well that the twist rates says it shouldn't even stabalize properly.
As to what twist rate is best for you, it all depends on what you want to shoot. Since you mentioned a target style AR, I'm guessing you're looking at shooting heavier bullets? In that case you'll probably be best served with a fast twist rate, such as 1:8" or 1:7" In a lot of cases, guys in this situation first decide on what bullet they'll be shooting and then choose the twist rate to match!
To further clarify, it isn't so much the weight of the bullets as it is the length of them. Generally speaking though, heavier bullets = longer bullets.
As indicated, the Hornady 75 grain Amax, 80 grain SMK, 80 gr. berger VLD, and a host of other heavy bullets are too long to seat to magazine length, therefore need to be seated longer and single fed into an AR action.
The 1:12 twist was designed for the 55 grain FMJ, and should shoot bullets in this weight/length well.
I don't see much point in having an AR that will shoot 40 grain varmit rounds, so a 1:7 or a 1:8 would be my recommendation. They will shoot 55gr and up well.
Wolverine carries a 1:8 twist 'NM' type barrel made by Armalite. The pricing is decent, and these barrels shoot really well.
As indicated, the Hornady 75 grain Amax, 80 grain SMK, 80 gr. berger VLD, and a host of other heavy bullets are too long to seat to magazine length, therefore need to be seated longer and single fed into an AR action.
The 1:12 twist was designed for the 55 grain FMJ, and should shoot bullets in this weight/length well.
I don't see much point in having an AR that will shoot 40 grain varmit rounds, so a 1:7 or a 1:8 would be my recommendation. They will shoot 55gr and up well.
Wolverine carries a 1:8 twist 'NM' type barrel made by Armalite. The pricing is decent, and these barrels shoot really well.
