Best twist rate for 62 grain and 77 grain 5.56 mm ammo?

[Grenadier]

Got a question for those who shoot AR-15-style rifles...

What kind of barrel twist will be best for the the 62 and 77 grain ammo?

Right now, my Bushmaster XM15-E2S carbine has a 1 in 9" twist, that's supposed to be good for stabilizing a wide variety of loads. I'm sure that it will handle the 62 grain loads fine, but what about the 77 grainers? Would a 1 in 7" be good for 55 through 77 grain loads?

 

[sgtmac_46]

Got a question for those who shoot AR-15-style rifles...

What kind of barrel twist will be best for the the 62 and 77 grain ammo?

Right now, my Bushmaster XM15-E2S carbine has a 1 in 9" twist, that's supposed to be good for stabilizing a wide variety of loads. I'm sure that it will handle the 62 grain loads fine, but what about the 77 grainers? Would a 1 in 7" be good for 55 through 77 grain loads?

The 1:7 is better for heavier loads.......you need to decide what loads you are going to shoot, as the 1:9 or 1:12 are better for lighter bullets.

1:9 is okay all around if you can't decide what loads you want to shoot.

 

[Grenadier]

The 1:7 is better for heavier loads.......you need to decide what loads you are going to shoot, as the 1:9 or 1:12 are better for lighter bullets.

1:9 is okay all around if you can't decide what loads you want to shoot.

Thanks.

I primarily shoot Winchester Q3131A 55 grain FMJ from my Bushmaster, which works great with the 1 in 9".

I am, though, contemplating buying a separate upper, or maybe just the barrel, in order to accomodate the heavier loads.

 

[sgtmac_46]

Thanks.

I primarily shoot Winchester Q3131A 55 grain FMJ from my Bushmaster, which works great with the 1 in 9".

I am, though, contemplating buying a separate upper, or maybe just the barrel, in order to accomodate the heavier loads.

Yeah, the super-fast twist of the 1:7 tends to play hell with really light loads......but nothing stabilizes a heavy load like the 1:7.

 

[Archangel M]

Rule of thumb:

Heavy loads 1:7

Lighter loads 1:9

Light loads in the 1:7 have a possible risk of separating the jacket from the core when "overspun".

 

[terrylamar]

1:8 twist in a match barrel is an excellent choice for 62 grain bullets, and a good choice for 77 grain bullets.

1:7 twist is an excellent choice for 77 grain bullets and a good choice for 62 grain bullets.

 

[searcher]

I am currently running a 1:7 for all of my loads in my M4. I am thinking I will get a 1:9 in my next rifle, itis going to be for some 45gr. loads. Seems to me like is is a matter of preferance. The more the twist the higher the spin rate which leads to more stability.