New AR15 upper with twist rates of 8 or 9 inches per turn

timujin · January 31, 2001, 07:05 PM

When our local gun show comes back in February I plan to buy a flat top upper with a stainless steel 16 or 20" barrel so I can mount my 12x Leupold for some 100-300 yard target shooting. I noticed some of the uppers come in 1 in 8
and 1 in 9 twists. Does it make that much of a difference?

I usually shoot 55 gr bullets and plan to shoot the heavier bullets that are now available. Thanx..........Mike

Jeff White · January 31, 2001, 07:52 PM

Mike,
The original AR15 had a 1/14 twist barrel. This twist proved not accurate enough for the Army during the Arctic Test phase, so they specified the 1/12 twist. This stabilized the 55 gr M193 bullet in the dense arctic air so that the rifle was acceptable for use in all climates.

This was fine until the adoption of the Belgian SS109 bullet as the Nato standard ammunition. This bullet is heavier (62 gr) and longer then the M193. The US Army adopted this round as standard for the M16A2 and the M249 Squad Automatic Weapon in 1985 and designated it the M855. The M855 was most accurate out of a twist of 1/8. Contrary to popular belief, it's not the weight of the bullet that causes it to need a faster twist to shoot accurately, but the length. Even 1/8 twist was not fast enough to stabilize the Tracer round that the Army adopted (M856) which is much longer then the M855 round. So the new family of weapons received barrels with 1/7 twist barrels.

There are a lot of old wives tales floating around that say you can't shoot the lighter weight bullets from 1/8 or 1/7 twist barrels. This is untrue. Some people have experienced problems with very light weight and thin jacketed varmint bullets out of 1/7 twist barrels, but the construction of the bullet has as much to do with that as the twist rate of the barrel.

The lighter bullets will be just as accurate out of the faster barrels but the zero will change. I/9 is a good compromise, fast enough for the longer, heavier bullets but not so fast that fragile varmint bullets will break apart in flight.

HTH

Jeff

Nukem · February 1, 2001, 07:40 AM

I like the 1-9" as a good all around twist in the AR. I built my Service Rifle in 1-8", just because I never shoot anything lighter than the 69gr. in it.

kgs · February 1, 2001, 11:48 AM

Go with the 1/9 twist. It's a good all-arounder.

kgs.

Don S · February 2, 2001, 07:20 PM

The 1 in 9 will stabilize the Hornady 75 gr. HPBT, and lighter weight bullets. It may stabilize the 75 grain Hornady A-max. It won't stabilize 80 grain bullets.

Or to put it another way, it will stabilize any bullets that will seat so the cartridge will feed through the magazine (except the military tracer).

timujin · February 2, 2001, 10:51 PM

Thanks for the info fellows, I will look for a 1 in 9 when I do my looking later this month..........Mike

January 31, 2001, 07:52 PM	#2
Jeff White Senior Member Join Date: October 29, 1998 Location: Kinmundy, IL, USA Posts: 1,397	You Need the faster twist to shoot the heavier bullets Mike, The original AR15 had a 1/14 twist barrel. This twist proved not accurate enough for the Army during the Arctic Test phase, so they specified the 1/12 twist. This stabilized the 55 gr M193 bullet in the dense arctic air so that the rifle was acceptable for use in all climates. This was fine until the adoption of the Belgian SS109 bullet as the Nato standard ammunition. This bullet is heavier (62 gr) and longer then the M193. The US Army adopted this round as standard for the M16A2 and the M249 Squad Automatic Weapon in 1985 and designated it the M855. The M855 was most accurate out of a twist of 1/8. Contrary to popular belief, it's not the weight of the bullet that causes it to need a faster twist to shoot accurately, but the length. Even 1/8 twist was not fast enough to stabilize the Tracer round that the Army adopted (M856) which is much longer then the M855 round. So the new family of weapons received barrels with 1/7 twist barrels. There are a lot of old wives tales floating around that say you can't shoot the lighter weight bullets from 1/8 or 1/7 twist barrels. This is untrue. Some people have experienced problems with very light weight and thin jacketed varmint bullets out of 1/7 twist barrels, but the construction of the bullet has as much to do with that as the twist rate of the barrel. The lighter bullets will be just as accurate out of the faster barrels but the zero will change. I/9 is a good compromise, fast enough for the longer, heavier bullets but not so fast that fragile varmint bullets will break apart in flight. HTH Jeff

February 2, 2001, 10:51 PM	#6
timujin Member Join Date: May 14, 2000 Location: magnolia, ky, usa Posts: 64	Twists & turns Thanks for the info fellows, I will look for a 1 in 9 when I do my looking later this month..........Mike

January 31, 2001, 07:05 PM	#1
timujin Member Join Date: May 14, 2000 Location: magnolia, ky, usa Posts: 64	When our local gun show comes back in February I plan to buy a flat top upper with a stainless steel 16 or 20" barrel so I can mount my 12x Leupold for some 100-300 yard target shooting. I noticed some of the uppers come in 1 in 8 and 1 in 9 twists. Does it make that much of a difference? I usually shoot 55 gr bullets and plan to shoot the heavier bullets that are now available. Thanx..........Mike

February 1, 2001, 07:40 AM	#3
Nukem Senior Member Join Date: January 29, 2000 Posts: 709	I like the 1-9" as a good all around twist in the AR. I built my Service Rifle in 1-8", just because I never shoot anything lighter than the 69gr. in it.

February 1, 2001, 11:48 AM	#4
kgs Senior Member Join Date: December 17, 2000 Posts: 142	Go with the 1/9 twist. It's a good all-arounder. kgs.

February 2, 2001, 07:20 PM	#5
Don S Senior Member Join Date: January 18, 2001 Posts: 100	The 1 in 9 will stabilize the Hornady 75 gr. HPBT, and lighter weight bullets. It may stabilize the 75 grain Hornady A-max. It won't stabilize 80 grain bullets. Or to put it another way, it will stabilize any bullets that will seat so the cartridge will feed through the magazine (except the military tracer).