[VTLO910]

My best friend and I were talking about AR's... No surprise there...

He stated that certain bullet weights work better from a 1:7 Twist vs. a 1:9 Twist...

Since I have limited knowledge in this area, I thought I'd open the discussion to see what everyone's thoughts were on it...

 

[Jeff]

The 1/7 are better with heavier bullets. I think the 1/7 was chosen for the military M4 rifles so they could stabilize both the ball ammo and the heavier tracers (77gr?). 1/9 will stabilize a lighter bullet better than a 1/7.

 

[Machinator]

What Jeff said. The twist rate is how many twists per inch of the barrel, so the lower number is the faster twist. Faster twist is required to stabilize heavier bullets.

A 1/7 likes 62gr and up ammo but would overspin (for less accurate shots) a 55gr. My 1/9 enjoys the 55gr well enough, but some have said 62gr is more accurate.

Slower twist rate ARs are usually intended for varmint hunting, using the 40-50gr bullets, whereas a fast 1/7 twist might spin those bullets to death or cause them to tumble.

 

[winemaker]

Here's a good source of all things .223/5.56:

http://www.razoreye.net/mirror/ammo-oracle/AR15_com_Ammo_Oracle_Mirror.htm#diff

 

[Les]

What Jeff said. The twist rate is how many twists per inch of the barrel, so the lower number is the faster twist. Faster twist is required to stabilize heavier bullets.

I think this is half right. The twist rate, like 1:7, is the rate of one turn in seven inches, not the twists per inch. But you are right in that the lower number would be a faster twist, 1:7 would be one turn in 7 inches where 1:9 would be one turn in 9 inches.

 

[Machinator]

I think this is half right. The twist rate, like 1:7, is the rate of one turn in seven inches, not the twists per inch. But you are right in that the lower number would be a faster twist, 1:7 would be one turn in 7 inches where 1:9 would be one turn in 9 inches.

Sorry, I said that goofy. You're right, twists over inches is correct. Per 7 inches of barrel, there's one twist of the rifling. Not per inch.

 

[tinker]

From what I know, everything posted is correct. In my experience, acuracy at under 200 yards is not totaly thrown off because of wieght to twist ratio. My Sig 556 has a 1/7 and seems to prefer 62gr, but I can still group almost as nice with 55gr. Last time I went up to Sig we were nailing steel plates at 300 yards with Federal 55gr using red dot sights.
So for me, I don't get worked up too much on bullet weights, but by no stretch of the word am I a marksman. Perhaps people who can shoot very tight groups at long distances will best see the effect of bullet weights.