[Glasshartt]

So, what are the advantages or disadvantages of a 1:7 over a 1:9 twist?

[dnthmn2004]

Correct me if I'm wrong, but 1:7 is more geared towards full auto with 5.56

[Jpyle]

Originally Posted by Glasshartt

So, what are the advantages or disadvantages of a 1:7 over a 1:9 twist?

Civilian use they are probably limited but I believe the 1:7 was developed for the M4 to get the heavier armor piercing and tracer rounds stabilized more quickly out of the 16" barrel.

[Quentin]

Originally Posted by Glasshartt

So, what are the advantages or disadvantages of a 1:7 over a 1:9 twist?

Well it depends on the ammo you normally use but in general you'd expect the 1:9 twist to do better with 62gr and lighter while the 1:7 would do better with 62gr and heavier. There is some overlap around 62 grains where either would be fine. Of course each barrel is an individual so we can only talk in generalities right now.

[Glasshartt]

So the only deciding factor would be what bullet weight you want to use??

[Quentin]

Originally Posted by Glasshartt

So the only deciding factor would be what bullet weight you want to use??

For which twist rate to choose, yeah that's it basically. But it's never that easy, first we're talking plural, which bullet weights (or lengths if you want to look at it that way). And then with any barrel there are compromises so you may find exactly what you want except with a different twist.

Honestly if you ever think you'll want to try out long heavy rounds, then go 1:7. Conversely if you think you'll want to drop down to 50gr or under then go 1:9. If you'll go exclusively with 55-69gr it probably doesn't matter which way you go. At the time the M16A2 was developed the military went with 1:7 mainly because their long tracer rounds wouldn't stabilize well in 1:9.

[Sniper03]

Quentin,

Just to explaining the 1:7 issue. The reason I kept the 1:7 specs at 77 grain max. Is that most all 1:7 ARs and military M-4s are tactical weapons and used for military. LE and similar weapons. Therefor to shoot the 80 grain bullets would in all probability require hand or single round loading due to the AOL of the round. Didn't want someone going out with a defense weapon thinking the 80s would feed without any problems in a critical situation. Like the guy that would load his magazine with some 80s and never check it to see if they would feed. Most of the guys that shoot the 80 Grains out of the 1:8 are varmint shooters doing some long range work. And feed a round one at a time or from the special single round sold follower magazines that are available or just hand load one round at a time in the chamber. If all that makes sense? You are correct about the 1:7 twist being able to shoot them for sure! Thanks for reminding me I should have explained that in the tread.

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[ZombieKiller83]

Figure i'll add that my BCM 16" 1:7 has fired 55gr 5.56 and 2.23 fairly accurately as well

[Vincine]

1:7, 1:9, 1:12, etc?

Clearly I don’t know much about this stuff, but wouldn’t/shouldn’t the rifling twist rate smoothly increase from where the bullet enters the barrel to where it exits the barrel?

[JonM]

1:x means the rifling twists the bullet 360 degrees of rotation in X inches of length. not sure what you mean about smooth.