AR cast plinker 1:14 barrel twist?

[TenTea]

Larry Gibson and some of the old posters here used to speak well of a 1:14 barrel twist for an AR15 and cast bullets.
I have had a 1:12 on backorder for awhile but have a chance to acquire a 1:14 made by Green Mountain.
It's 20 inches in length and chrome lined.
I know that 1:14 twist is a popular choice for varminters shooting light bullets at high velocity but that is not my goal.
I am loading Saeco 221 bullets sized @ .225", lubed and gas checked, along with RL7, Unique and/or IMR4895.
The bullets weigh ~63 grains when they are all dolled up with lube and gas check.

Questions:
Will this combination (bullet & barrel) be accurate for 50 to 100 yard precision plinking?
Ought I remain patient and hold out for the 1:12 twist barrel?

Please post any thought or experiences.

Thanks!

[kbstenberg]

watching with interest.

[TenTea]

To add...

When I use Greenhill's formula, I get 11 for an optimal barrel twist.
Do you think that is set in stone? It's closer to 12 than 14, that's for sure...

The “rule of thumb” formula for twist rate, developed by George Greenhill, is:
Twist = (C x [Bullet Diameter in Inches, Squared]) / [Length of Bullet in Inches]
Where “C” is 150 when the velocity is under 2,800 feet per second, and 180 when above. There’s some extra bits that are thrown in when you don’t have a lead core projectile, but that’s the basics. This formula can be used to either figure out the ideal twist for a given projectile, or figure out what the ideal length of projectile for a given twist is.

11= (150 X [.2245 X .2245]) / .6845

[TenTea]

Some tidbits from the innerwebs (including here)...I'm trying to elicit some response to this thread from youse guys!

* I use Saeco bullet mould #221, 60 gr spitzer tumble lubed and sized .224 using Lee sizer. No gaschecks. Using 20 grains (recommended 22 grs) of Vitovhourri N120 powder and dried laundry lint as filler have shot 100 rounds for plinking in an Elisco M16A1 rifle, full auto sometimes with no jamming and no feeding problems. But I had to spray the chamber and gas port with WD 40 after firing as a precautionary measure to clean the gun . It was an experiment to try to do so if it will work. It did, but am now considering powder coating my cast bullets.

* I shoot the Saeco 221 in both 223 and 22-250, but both are 1-14 twist. My 221 bullet with gas check is 58 gr. WW and tin, 20:1. 21 gr. Varget in the 223 is about 2,200 fps and under 1 inch. The 22-250 with 24 gr. IMR 4895 is about 2,300 and under 1 inch. Both Kill small game well. For better groups I drop both loads down about 5 grains.

* Apparently [redacted] has a good handle on it and that's why he's wanting a slower twist AR for shooting cast bullets. As far as standard AR twists the 12" will be the best if he can find one. But since he is building the rifle there are many 'smiths out there that can turn a standard 14" twist barrel to AR contours. The standard 20" barrel would do if [redacted] wants a "handy rifle but if not a heavier 24" barrel would be better. The standard rifle length gas tube would work best for the milder pressured cast bullet loads. I also would get a military chamber for the M855 cartridge. This will allow the seating of 55 - 60 gr cast bullets so the GC stays in the case neck. One last thought; since this is a cast bullet AR consideration might be given to the .222. The .222 is easily formed from .223 cases, will feed from the magazine with no problems and the longer neck makes it more cast bullet friendly....just a thought.

* The use of medium to slow burning powders from 4895 to AA4350 would be where I'd start with a 14" twist barrel. The best all around cast bullet for the .223 for me has been the 225462 Lovern style. The down side is the 2 front lube grooves are outside the case neck. Some years ago i found success with that bullet using H4895 in a 12" twist Colt AR at 22-2300 fps. That load has served me well in other 12" twist ARs and just so-so in 9" twist ARs over the years. I've 7, 9 and 12" ARs so I guess I'm going to have to revisit cast bullets in the .223 in the AR. I really don't expect the results to be much different that they are in my 9, 12 and 14" twist bolt guns though.

* Definitely do the 14" twist barrel if you are putting it on yourself. I think you'll be quite pleased. You should get into the 24-2500 fps range with pretty good accuracy (2 moa if the rifle and cast bullets are up to it) without too much problem. Above that it does get a little tricky and requires attention to detail a lot more.

[TenTea]

To add...

When I use Greenhill's formula, I get 11 for an optimal barrel twist.
Do you think that is set in stone? It's closer to 12 than 14, that's for sure...



11= (150 X [.2245 X .2245]) / .6845

I also read that using *180* as the constant for a .22 bore AR15 is appropriate, due to velocities being comparatively high.

(Where “C” is 150 when the velocity is under 2,800 feet per second, and 180 when above.)

So, then...

13.25 = (180 X [.2245 X .2245]) / .6845

When figured that way at 13.25, we are closer to an optimal 1:14 barrel twist for the Saeco 221 bullet.

I don't see loading to over 2800 fps, but I suppose one could.

[Moleman-]

Haven't used cast in my 223 ar's yet but have in a 9mm gas op, 357Max rimless, and soon a .44x1.7-1.8" rimless. I do have a 1:14 ar15 barrel and my only caution would be if you plan to shoot much j-word bullets above 55gr. Mine won't stabilize 62gr ss109 but does fine with 55gr. Thought it was a 1:9 as it was on a used A2 I bought up until it keyholed the first time out and found it was a 1:14"

[TenTea]

I do have a 1:14 ar15 barrel and my only caution would be if you plan to shoot much j-word bullets above 55gr. Mine won't stabilize 62gr ss109 but does fine with 55gr.

This iron sighted A2 upper will be purpose built for cast bullets only and 3-position shooting from 25 to 100 (maybe 200) yards.

[Harter66]

I had hoped to see other inputs also .
The 223 I had was 1-8 so no help there except that WCWW in NOE 225-55 @ 62 gr gives the same 2.5" as random fmj from the shelf of 55&62 gr . (PMC , Tula etc from the cheap seats) The load here is to mag length ,Tapco poly , and a start load of H322 for a a jacketed bullet of 65 gr based on combined data from Sierra ,Speer , Horn and Lyman books . ( Further disclosure, the rifle was a very inexpensive, no mods , zero nothing ATI Omni Hybrid with a Buriss 197? scope that was laying on a shelf from a pig in a poke box . Good sights and almost any flash hider other than the M4 bird cage would certainly improve groups.)


A 222 with I think a 12 twist shot as well with the 50 gr Bator and the NOE as with FC ,Horn ,Rem and Win 50 gr SP of each brand circa 1982 .

The actual real surprise came over the Chrony with the 50 gr original Bator clocking 1700 fps with I think 4 gr of 1968 lot Unique . H4198 ran into the 2300s delivering field groups of 1.5 with the NOE bullet .

Disclaimer this was a Savage 340 with a 24" bbl and all shot field positions ,so sitting sling wrapped or post/limb rest at 100 yd . I got groups as good as factory ammo that I'm certain were much bigger than the rifle is capable of and stopped the work up and loaded 140 rd in Winchester brass as that was what I had and worked up.

[TenTea]

So, my primary AR has a 1:9 twist tube and I have loaded and fired some cast bullets on a preliminary test basis.
Results were promising with good accuracy at 50 & 100 yards...perfect for my iron sight practice shooting needs.
My best load was the aforementioned Saeco 221 / gas checked, over 14 grains or RL7, which was the minimum powder charge to fully work the action of the rifle.
That rifle is topped with an optic now and I miss my iron sight practice.
I was hoping to get *even better* results downrange by assembling a dedicated cast bullet upper to use when the mood strikes.
My first instinct was 1:12 but the question regarding 1:14 has been on my mind.
If I wait long enough on backorder, I figure to get the 1:12 barrel someday, but a man gets impatient to continue on with handloading projects before the snow flies!

[Tackleberry41]

A cast bullet tends to be shorter than jacketed. So while 1-14 may be slow for a 55 gr jacketed, my 22 hornet H&R will shoot a 55gr lyman fine.

[TenTea]

A cast bullet tends to be shorter than jacketed. So while 1-14 may be slow for a 55 gr jacketed, my 22 hornet H&R will shoot a 55gr lyman fine.

I take it you would vote favorably for a 1:14 twist with cast bullets ~60 grains then?

[Rattlesnake Charlie]

Twist rate depends more on bullet length. A long 60+ gr bullet may well need 12".

[Tackleberry41]

it would depend on the bullet. In my subsonic experiments w 223. A flat based 60gr would work in a 1-9, but not a boatail. That little shift in point of balance changes things. And I only have the one 55gr mold so no experience w a cast 60 gr.

[TenTea]

In regard to bullet length and food for fmj thought...

[Tackleberry41]

The reason the US military went with the 1-7 twist was solely to stabilize the longer 62gr tracer.