Twist Rate For a 55gr 5.56 Bullet

[345 DeSoto]

I've given up on trying to find a 12 twist 20" barrel for the .223 AR15 I'm putting together. I HAVE found a few 9 twist 20" barrels that I'm interested in. Is this a good twist/length for accuracy out to 300 yards, using 55gr BTHP? I'm using 40gr BT in my 12 twist Savage Model 10, 22-250, and that weight bullet is a tack driver at 300 yards. I figure the faster twist in an AR autoloader could use 55grns. Need some solid advice on this, before I sink a lot of $$$ into something totally wrong. Thanks, guys...

 

[243winxb]

9 twist ok with 55gr bullet. http://www.6mmbr.com/223rem.html Twist Rate Stability Calculator http://www.bergerbullets.com/twist-rate-calculator/ I am shooting a Savage 1-9 with Nosler 55 BT bullets. Works well. Its the length of the bullet that counts, not weight.

 

[LocoGringo]

It's hard to say 'cause I'm not sure what kind of accuracy you are wanting at 300 yards.

I have a 20" melonited barrel that is a .223 Wylde chamber, 5-R rifling, 1:8 twist that is stupid accurate. I also have an 18" barrel with the same specs by the same maker and I'll give you a quick anecdote. Prepping for a major 3-gun match, I went to a 300 yard range to find my aiming point for that distance with 55 grain PMC Bronze ammo. After I found the aiming point, I tried for a 5-shot group using a 6 power scope. I managed 3 rounds in a perfect horizontal line that measured 1.1" with 1 more round at 3 o'clock about 2.5 inches from the "3" and another round at 6 o'clock about 3 inches away from the "3". Not stellar results, but I was impressed by the "3" considering the ammo and lack of scope magnification.

A 1:9 or a 1:8 may not be ideal, but they are still capable of excellent accuracy if it's a good quality barrel.

 

[spitballer]

No search is complete without checking with Jay at Pac-Nor barrels.

 

[Cemetery21]

Or John at White Oak...
http://www.whiteoakarmament.com/xcart/product.php?productid=17825&cat=312&page=1

 

[ArchAngelCD]

Why would you want to put a 12 twist barrel in an AR rifle? With all the new and high quality heavier bullets available today why would you want to limit yourself to bullets 60gr and under? My AR-15 has a 9 twist barrel but if I did it over it would be a 8 or even 7 twist barrel.

A 9 twist barrel will be just fine for shooting 55gr bullets. That is what I mostly shoot in my 9 twist barrel even though I could go heavier. I have a bolt action rifle with a 12 twist and I shoot 55gr bullets in that all the time with extremely good success so there is no reason why a 9 twist would do as well and better.

 

[MEHavey]

One-in-12 is a slow twist for 22-250/220 Swift velocities w/ light bullets out of 26" barrels, not a 223/AR.

Go with 1-in-9 for the AR.

 

[HexHead]

M16A1 used a 1:12 twist. It's the optimum rate for 55 grain bullets. According to a chart I saw from Brownell's, max bullet weight for 1:12 .223 is 63 gr.

Last year Weatherby changed the twist on their .223 Vanguard 2 rifle to 1:9. I'm glad I got my 1:12 when I did since I load 55 grain.

 

[MEHavey]

Having three AR-platforms, starting with a 20" Colt HBAR, I learned the hard way that twist rate matters if there is going to be any hope of wide bullet selection.

That 1-9 HBAR would not shoot anything over 65 grains w/o falling apart. So I called Bill Krieger to ask his opinion. His response was a replacement 1-7.7 twist barrel and I have never looked back:



So how does it do with light bullets ?
Not bad either:



My suggestion is therefore to go fast[er].
...unless you're going to drive thin-skinned 35gr grenades to 220Swift velocities that is.




Useful reference here:
http://thefiringline.com/forums/showpost.php?p=5538591&postcount=2

 

[bfoosh006]

I also believe in faster twist barrels.... all my 1n7 shoot Federal's 50gr Tipped Varmint ammo VERY accurately.

$7.99 / 20 at PSA.

I have only seen one instance 25+ years ago where a 1n7 AR barrel did not like a bullet... and that was the early very thin jacketed Fed. 40gr JHP.

 

[RugerOldArmy]

The only cases I've seen with a barrel twist being too fast causing problems are:

- Thin jacketed bullets designed for lesser cartridges being pushed much faster and flying apart.

- Patched roundballs in a muzzleloader

I'm in the 'Go with 1-7" or 1-8"' camp.

 

[joem1945]

The 1/9 twist should do well with 62 to 69 gr bullets. I built a retro SP1 that has a 1/12 twist and I use 55 gr bullets in it.

 

[NWcityguy2]

The barrels you are looking for are here...

M4 feed ramps: http://www.gmriflebarrel.com/m16-a1-5-56mm-20-1-12-twist-20-barrel/
M16 feed ramps: http://www.gmriflebarrel.com/gm-m32-m-16-pencil-profile-20-long-1-12-twist/

Green mountain makes good barrels too. I know guys who shoot 1:12 still, if 55gr in your max bullet weight then 1:12 is the perfect way to go. Remember with most AR barrels, and certainly anything chrome lined, your accuracy will be limited. That said I can shoot match bullets into 1 moa groups with my Green Mountain barrel which has a 1:8 twist.

Remember you can get accuracy from any twist rate. It's all about what bullet weight you want to shoot. All things being equal, I prefer 1:8.

 

[MEHavey]

1:8

that's a +1

 

[kerreckt]

Agree. 1:8