1:7 in an AR seems optimal to me because it allows shooting of everything up to 80 grains. So why are most manufacturers offering 1:9?

possibly because of light bullets, i've got a old colt 1:7 that won't handle 50 grainers - it keyholes them. rare happening maybe, but does exist

I think the military went to the 1:7 twist for the use of the heavy ss109 ammo.
I have a 1:9 Bushmaster a3 with a bdc Springfield 4.5x14 that shoots Blackhills 69gr match in the sub .75 moa range and 55gr ball just at moa.
The 69gr is the heavest bullet I have tried. I have heard that some of the palma guys are shooting 1:7 long throated barrels with 90gr seated out (single loading) and keeping them ss at 1k.
hope this helps

The 1in7 was necessary to stabilize the longer tracers.

1in9 is a good compromise and usually shoots all factory length ammo good, ie up to 77gr.
I have a 1in8 bbl on my Service Rifle so I can shoot 80gr Sierras and heavy VLD's, loaded out to a longer oal and single loaded for the 600 yard stage.

500, note please the .mil is using rather short barrels and not getting all the velocity us .civ in our varmit rigs do. As such the spin diferential and occasional environmental issue (extreme cold) effects the performance the .mil requires. The specific use of ammunition types and it's fragmentation also require more spin than a Nosler BT to expand in our .civ terminology. Many now use a 1 in 8 for 18" and longer barrels, and I would suggest you querre Mr John Hollinger whom I undersatnd also graces this forum on occasion.

I have a Shilen barrelled 8 twist put together by White Oak that shoots 80 grn bullets just fine. The rifle is used in service rifle competition. John Holliger builds a fine AR.
Butch

Many now use a 1 in 8 for 18" and longer barrels, and I would suggest you querre Mr John Hollinger whom I undersatnd also graces this forum on occasion.[/QUOTE]



He would probably grace it more if he didn't get attacked by the forum "experts" every time he expresses an opinion.

Recent AR15 trigger discussion comes to mind.

For future reference, if you see Gasgunner and AR15 in the same post, pay attention.

Just a tip for those that actually want to learn something.

From personal experience, I have seen 9 twist rifles that will shoot 77 MK and others that will not.
I've never personally seen a 1/9 twist explode a light varmint style bullet.
I have seen 1/8 and 1/7 blow up blitz type bullets.

It depends on the rifle as a 1/9 rifle could actually be a 1/9.4 or a 1/8.6.
Some rifleing machines aren't as precise as we would like them to be.

Covey16

Why is there so many different rates of twist in weapons .

Well I suspect it has something to do with all those bullet manufactures offering almost every conceivable bullet weight in what ever caliber !.
Short twist heavy bullets long twist lighter bullets . ...