Need info on AR barrel twist rates.

[Cuz]

Hello,
I'm trying to get some information/research about the different barrel twist rates for AR15 rifles. I tried searching but kept coming up empty. I want to learn more about the different twist rates available with AR15 rifles and what are the pros and cons for each.
Thanks,
-Cuz.

 

[vellnueve]

1-12 - made for M193 55 grain ball. - was standard on vietnam era M16s and M16A1s
1-9 - made for M855 62 grain ball - I think this was used on the A2
1-7 - made for heavier bullets, such as 77 grain match stuff - standard on today's M16A4s and M4s

In general, heavier bullets are better off in a faster twist.

 

[Cuz]

1-12 - made for M193 55 grain ball. - was standard on vietnam era M16s and M16A1s
1-9 - made for M855 62 grain ball - I think this was used on the A2
1-7 - made for heavier bullets, such as 77 grain match stuff - standard on today's M16A4s and M4s
In general, heavier bullets are better off in a faster twist.

Thanks Vellnueve. That's a great summary to keep handy. I'll print it and keep in my reference pile for future use. If anyone has any in-depth research data or reading material regarding this subject please send it my way.

-Cuz.

 

[In_God_We_Trust]

1-12 - made for M193 55 grain ball. - was standard on vietnam era M16s and M16A1s
1-9 - made for M855 62 grain ball - I think this was used on the A2
1-7 - made for heavier bullets, such as 77 grain match stuff - standard on today's M16A4s and M4s

In general, heavier bullets are better off in a faster twist.

+1 Very good summary!

 

[LoginName]

+1 Very good summary!

+1

Now for the complicated version...

http://www.ammo-oracle.com/body.htm

 

[Chuck Would]

AR Education

If you REALLY want to learn about the AR, I suggest a couple different books that are available from Fulton Armory: http://www.fulton-armory.com/ Site Search for AR books and you'll find them:
The AR-15 Complete Assembly Guide
—How to build your own AR-15
—by Walt Kuleck with Clint McKee.

The AR-15 Owner's Guide (2000) by Walt Kuleck and Scott A. Duff.

Those two books will tell you more about the AR than you really want to know.

Hope that helps,

 

[Snapshot]

Bullet weight is a long standing myth. It's really about bullet length. It just so happens that the two usually are similar as long as you are always shooting jacked lead. The moment you start using Barnes copper bullets, hollow points, poly-tipped, tracers, steel-core, solid lead or anything else, the weight method will steer you wrong.

What you want use is the greenhill formula which is:
T=150(d/r) for velocities to 2800 fps
T=180(d/r) for velocities over 2800 fps

Whereas T = The slowest recommended twist rate needed to stabilize the bullet
D = Bullet Diameter
R = The Ratio of the bullets length to diameter

For the bullets I've tested, the twist rates are as follows
http://spreadsheets.google.com/ccc?key=pPyocBiTtKbBTw-058YWfcg&hl=en

As you can see from that spreadsheet: Both the Sierra 165gr Hollow Point Boat Tail and the Barnes 130gr Tipped TSX solid copper round both need a 1:12 (or faster) twist rate to stabilize the round even though there is a 35gr difference between them.

 

[doobie]

The barrel I just ordered is 16" and has a 1/16 twist.... for 22LR

 

[vellnueve]

I'm wondering how my .22 Ciener kit will perform in my 1/7 barrel.

 

[doobie]

I'm wondering how my .22 Ciener kit will perform in my 1/7 barrel.

Once I get my upper, you are welcome to come up to NH and we can compare.

 

[bpm990d]

The problem with the .22 kits has more to do with the diameter of the bore and grooves than it does with the twist rate.

The bore and groove of an AR barrel are typically .218 & .224. For a rim fire they are typically .215 ~ .217 with a groove diameter of .222. Spinning the bullet to fast is much less of a problem than spinning it too slow.

B