AR-15 Twist Rate information.

[Bill2905]

Buds Mini 14 ranch ( earliest model ) would rip apart Hornady 55gr SX. Dunno what twist rate was. Said bore wasnt the most smooth.

Got a .219 D Wasp and dunno what the twist on it is. 50gr Nosler BT do sub half inch at 100. Supposedly nips at 22-250 heels....I dont have a chrono.

Not interested either. Its hot enough and accuracy is there. No need to try to squeeze out more of either.

Do think 55s in an AR about perfect yote machine. Tried across 3 different ones.....the V max or Winchester Supreme stuff both shot well.

Exits kinda large but can be sewed up LOL

While fast twist barrels will stabilize the lighter bullets, some lightly constructed varmint bullets will come apart upon exiting the muzzle if they are spun too fast. I think it's just a trial and error process as it is hard to predict when it may happen.

 

[DadSmith]

While fast twist barrels will stabilize the lighter bullets, some lightly constructed varmint bullets will come apart upon exiting the muzzle if they are spun too fast. I think it's just a trial and error process as it is hard to predict when it may happen.

Which is why I think ar pistols should have a 1/9 or 1/12 twist so you can shoot the lighter bullets and gain velocity where you lose it with heavier bullets in a short barrel.

 

[Hkindiana]

The M4 has been 1-7 from the beginning even the M16 went to 1-7. It's been 1-7 since the 1990's at least. My 1-8 will shoot some 55gr good but not all. It likes 75gr bullets the best. The only 62gr bullet it shoots accurate is Wolf Military Classic 62gr HP that I have found so far. It doesn't like M193 or M855. At least the federal version. 1-12 will shoot 55gr and down to 35gr. My buddy has a varmint rifle with that twist and he uses 35gr and 40gr a lot for that high velocity.

1960’s to 1990’s IS 30 years, and 1/12 barrel twists WERE the US Military NORM with 55 grain bullets in the M16’s and variants of the day. The whole Vietnam war was fought by US trooos using 55 grain bullets in 1/12 twist barrels.

 

[DadSmith]

1960’s to 1990’s IS 30 years, and 1/12 barrel twists WERE the US Military NORM with 55 grain bullets in the M16’s and variants of the day. The whole Vietnam war was fought by US trooos using 55 grain bullets in 1/12 twist barrels.

"Testing soon showed that the British and Belgian designs were roughly equal, both outperforming the original U.S. design. In order to get full performance from tracer versions of the SS109, however, barrels would have to use different rifling. Existing 1-in-12 twist barrels reduced the effective range of the SS109 to 90 meters due to lack of stability. While the ideal twist rate for the SS109 projectile is 1-in-9, a 1-in-7 twist rate was chosen to stabilize the much longer L110 tracer. This tracer was designed to complement the SS109's ballistic performance. The M196 tracer (complement to the M193 ball round) had a burn-out range of 450 meters where the L110 tracer was bright to 800 meters. In the end the Belgian round was chosen. The U.S. Marine Corps was first to adopt the round with the M16A2, introduced in 1982. This was to become the standard U.S. military rifle. The NATO standard ammunition produced for U.S. forces is designated M855 for the ball round using a SS109 type projectile and M856 for the tracer using the L110 type projectile."

So according to the History of the M16 above the M16A2 came with a 1/7 twist in 1982. So M16A2 and up to modern M4 use 1/7 twist since 1982. Basically 39 years and counting for the 1/7 twist.

M16 Rifle General Information, M16, M16A1, M16A2, M16A3, M16A4

M16 RifleFrom Wikipedia, the free encyclopediaM16 is the U.S. military designation for a family of rifles derived from the ArmaLite AR-15 and further developed by Colt. It is an assault rifle which fires NATO standard 5.56 mm ammunition. It has been the primary infantry rifle of the United...

bravocompanyusa.com

 

[Hkindiana]

"Testing soon showed that the British and Belgian designs were roughly equal, both outperforming the original U.S. design. In order to get full performance from tracer versions of the SS109, however, barrels would have to use different rifling. Existing 1-in-12 twist barrels reduced the effective range of the SS109 to 90 meters due to lack of stability. While the ideal twist rate for the SS109 projectile is 1-in-9, a 1-in-7 twist rate was chosen to stabilize the much longer L110 tracer. This tracer was designed to complement the SS109's ballistic performance. The M196 tracer (complement to the M193 ball round) had a burn-out range of 450 meters where the L110 tracer was bright to 800 meters. In the end the Belgian round was chosen. The U.S. Marine Corps was first to adopt the round with the M16A2, introduced in 1982. This was to become the standard U.S. military rifle. The NATO standard ammunition produced for U.S. forces is designated M855 for the ball round using a SS109 type projectile and M856 for the tracer using the L110 type projectile."

So according to the History of the M16 above the M16A2 came with a 1/7 twist in 1982. So M16A2 and up to modern M4 use 1/7 twist since 1982. Basically 39 years and counting for the 1/7 twist.

M16 Rifle General Information, M16, M16A1, M16A2, M16A3, M16A4

M16 RifleFrom Wikipedia, the free encyclopediaM16 is the U.S. military designation for a family of rifles derived from the ArmaLite AR-15 and further developed by Colt. It is an assault rifle which fires NATO standard 5.56 mm ammunition. It has been the primary infantry rifle of the United...

bravocompanyusa.com

The history lesson you quoted gives the reason WHY we shifted from 55 grain ammo with 1/12 twist barrels. However, MY point was that 30 years of military service with 55 grain ammo in 1/12 twist barrels kind of negates your charts claim of 40 grain being the correct projectiles for use in 1/12 barrels.

 

[DadSmith]

The history lesson you quoted gives the reason WHY we shifted from 55 grain ammo with 1/12 twist barrels. However, MY point was that 30 years of military service with 55 grain ammo in 1/12 twist barrels kind of negates your charts claim of 42 grain in 1/12 barrels

The chart is showing what bullets work best for accuracy and stability with the different twists. It does not mean you have to use that specific weight. My friend has a bolt action in 223 and he runs 35-40gr for varmint hunting it's a 1/12. If he shoots 62 or higher they are very unstable. My 1/8 will definitely shoot his 35 and 40gr rds but not very well or much past 50 yards without tumbling. My 1/8 will shoot 55gr upto 77gr that I have tested but it loves 75gr the best. The only 55gr it likes is Fiocchi. When I say like I mean shooting moa at 100yds. I'm not saying 1-4 moa at 100yds.

Who knows some National Guard units may still have some very worn out M16's or M16A1 lol.

 

[Hkindiana]

The chart is showing what bullets work best for accuracy and stability with the different twists. It does not mean you have to use that specific weight. My friend has a bolt action in 223 and he runs 35-40gr for varmint hunting it's a 1/12. If he shoots 62 or higher they are very unstable. My 1/8 will definitely shoot his 35 and 40gr rds but not very well or much past 50 yards without tumbling. My 1/8 will shoot 55gr upto 77gr that I have tested but it loves 75gr the best. The only 55gr it likes is Fiocchi. When I say like I mean shooting moa at 100yds. I'm not saying 1-4 moa at 100yds.

Who knows some National Guard units may still have some very worn out M16's or M16A1 lol.

The US military, through testing AND “in the field use”, determined that 55 grain bullets “work best for accuracy and stability” with 1/12 twist barrels

 

[DadSmith]

The US military, through testing AND “in the field use”, determined that 55 grain bullets “work best for accuracy and stability” with 1/12 twist barrels

Now they use 62gr and it needs at least 1/9 and the longer tracer rds shot better in 1/7 so they went with 1/7 in 1982. That's 39 years almost 40 years with 1/7 twist. Things change they went from 20" barrels to 14.5" also. Like I said shoot what you want in whatever twist. However, for best accuracy and longer range stability try using the proper bullet for the twist you have.

 

[Bill2905]

I find it easier to look at this topic in terms of what is the heaviest bullet that a given twist rate will stabilize. It's a starting point from where you can experiment and determine what works best in your rifle.

This is the information posted on the Shilen barrel site for .224 centerfire and is what I have been using when selecting a new barrel or bullets for an existing barrel. These are generally accepted guidelines but they are certainly not written in stone. For example, many 223 shooters have good success in shooting 77 grain bullets in 1-in-9 twist barrels.

.224 CF
- 7" for bullets up to 90 gr.
- 8" for bullets up to 80 gr.
- 9" for bullets up to 70 gr.
- 12" for bullets up to 63 gr.
- 14" for bullets up to 55 gr.

 

[sloughfoot]

Age Verification - NRA

www.americanrifleman.org

A little information on twist rate and why the Army changed to 1-7

The 5.56 M855 was approved by use for use by NATO in the 1980's. One of the cartridges in that family was a tracer round. That bullet needed the 1X7 to stabilize it. That is the only reason because the 62 grain M855 stabilized fine.

The 5.56 FMJBT M193 was never adopted as a NATO cartridge, even to this day. Its proper name is 5.56 Mil-Spec. It is identical to the commercial .223 FMJBT in all respects although there are some commercial loadings at less pressure than Mil-Spec.

 

[Slapstick]

Now the solid copper 55gr rds you can probably shoot in a 1-7 because they are definitely longer than copper and lead 55gr. I think it is the length of the bullet that determines what twist will give it the best accuracy. Not an expert on this subject so I'm open for discussion and learning.

You are correct. It's not bullet weight that determine the best twist rate, it's bullet length. When almost all bullets where made of lead with a copper jacket it was a good rule of thumb to go by bullet weight since heavier bullets would be longer. That changed with the introduction of monolithic, (usually all copper) and light composite frangible , (usually made of pressed copper and tin with an epoxy binder) which are longer than their lead counter parts. So in short, longer bullet require faster twist rates.

 

[BigMoose]

One cool thing to me anyway, is the new Polish AK that Radom developed when they entered NATO, has a 1/9 twist. The reasoning being that when Deployed, the polish troops would often be supplied by another country with ammo. And they were never guaranteed if it would be 55 or 62.

the French were another country that has a lot of 5.56 in 55 grain laying about.

 

[blues bondsman]

 

[DadSmith]

Here is 62gr in 1/12 twist. He was shooting at 50yd and they were already starting to destabilize.

Now imagine 69gr, 75gr, 77gr, 80gr bullets in a 1/12 twist.

If all else fails try this.

Twist Rate Stability Calculator

Our newly updated Twist Rate Stability Calculator not only tells you what your SG is, but it also lets you know if you are reaching your optimized BC.

bergerbullets.com

 

[700 LTR 223]

My own experience with a 1 in 9" Remington 700 LTR with 20" barrel is very good accuracy with 52 Sierra MatchKing, 55 Berger and 69 Sierra MatchKing.

Have a 1 In 8" Rock River Varmint with 18" barrel that really shoots well with the Sierra 77 MatchKing and even shot the light 52 MK well.