# 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?


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## sgtmac_46

Grenadier said:


> 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.


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## Grenadier

sgtmac_46 said:


> 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.


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## sgtmac_46

Grenadier said:


> 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.


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## 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".


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## 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.


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## 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.


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