AR-15 Twist Rates?
- Thread starter NaOH
- Start date
1:7 will shoot pretty much everything - some thin jacket light hollow point will experience catastrophic bullet jacket failure in it -- but that seems to vary from lot of lot as I have shot 40gr Federal Blitz (now discontinued) out to 100m fine thru 1:7's. Despite the popular myth 55gr will not be "over stabilized" by a 1:7.
Not good for .22LR usage due to excessive leading and gasport fouling
1:9 good thru most loadings - will not stablise C78/M856(US Orange Tip)/L110 tracer.
As well depending upon who made the 1:9 it may or may not stabilise the 75 and 77gr BTHP's.
Same issues as 1:7 with .22LR
1:12 55gr M193 type ammo and old Tracer (US Red Tip)
.22LR works well except gasport fouling
1:14 55gr M193 type ammo (not so good in cold weather)
good for dedicated .22LR (gasport same caveats)
Not good for .22LR usage due to excessive leading and gasport fouling
1:9 good thru most loadings - will not stablise C78/M856(US Orange Tip)/L110 tracer.
As well depending upon who made the 1:9 it may or may not stabilise the 75 and 77gr BTHP's.
Same issues as 1:7 with .22LR
1:12 55gr M193 type ammo and old Tracer (US Red Tip)
.22LR works well except gasport fouling
1:14 55gr M193 type ammo (not so good in cold weather)
good for dedicated .22LR (gasport same caveats)
KevinB said:
Also the 1:8 twist is good for Sierra's 69gr BTHP as well. And the Sierra 80gr BTHP shoot very well.
I am pretty sure that Sierra design the 77gr bullet so it can be seated to fit the AR15 mag length as well.
When I was down at Camp Perry, a lot of the AR shooters shoot the 69gr or the 77gr BTHP!
Yes -- not many AR shooters in Canada use the 80gr SMK since it is not mag length.
By general rule the barrels can stabilize any of the lighter bullets if it can a heavier one (depending upon bullet profile - the Hornady 75gr are actually longer (and thus harder to stabilize/requires a tighter twist than the 77gr SMK's and 77gr Nosler)
By general rule the barrels can stabilize any of the lighter bullets if it can a heavier one (depending upon bullet profile - the Hornady 75gr are actually longer (and thus harder to stabilize/requires a tighter twist than the 77gr SMK's and 77gr Nosler)
oppy said:
What Headamage said, lots of trial & error because projectile stability is achieved upon adequate velocity and gyroscopic spin for the given projectile. Adequate gyroscopic spin and velocity is dependant on barrel length, twist rate, twist and barrel design and of course cartridge and projectile design. But as a general rule 1/8 twist will stabilize most 223/556 projectiles... in my opinion 1/8 is the best for those who want the most versatility from the 223/556. This seems to be supported by many shooters of the 556/223 who own 1/8 barrels.
twist rates
1:8 is a good compromise twist rate for nearly all bullet weights. However, I have noticed that virtually all the 1:8 barrels available seem to be have a bull barrel contour, unlike 1:7 and 1:9 which are availalbe in lighter contours. Anyone seen 1:8 barrels available in regular contours?
1:8 is a good compromise twist rate for nearly all bullet weights. However, I have noticed that virtually all the 1:8 barrels available seem to be have a bull barrel contour, unlike 1:7 and 1:9 which are availalbe in lighter contours. Anyone seen 1:8 barrels available in regular contours?
