AR15.Com Archives
 1-12 Twist Barrels and Non M855 62 Grain Rounds??
Blain  [Member]
8/16/2011 12:50:09 PM
It is well known that the traditional 1-12 twist rate wasn't enough to stabilize the new M855 green tip penetrator round. Due to the steel core, the bullet was much longer than even a traditional FMJ bullet. My question is, what about a normal fmj or sp 62 grain bullet that is only slightly longer than the 55 grain M193 bullet? Will the 1-12 twist rate barrels stabilize that more often than not? I always figured that the notion against firing 62 grain rounds in 1-12 twist barrels was due to the much longer M855 vs. necessarily the 62 grain weight itself.
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urbanredneck  [Member]
8/16/2011 2:47:15 PM
My dad used to have a Remington 788 with either a 1:12 or 1:14 barrel. Very accurate rifle but at 200 yards the 55gr bullets would start to keyhole. I would guess that 62gr would prob be too much for that barrel.
Blain  [Member]
8/16/2011 3:16:28 PM
Hmmm....that doesn't sound right. Even 1-14 twist should stabilize 55 grain rounds unless it is very very cold and dense out.
twoofswords  [Team Member]
8/16/2011 3:34:35 PM
According to http://www.6mmbr.com/223rem.html

More versatile is a 1:12" twist that will allow you to shoot the popular 60-64 grain match bullets. (However, a 1:9" twist is needed for the steel-core 62gr bullet used in the M855 military loads, because that bullet is as long as most 70-grainers.)
TeeRex  [Team Member]
8/16/2011 3:40:52 PM
There may be some 62 grain bullets that work. Just off the top of my head wideners has a bulk lead core 62 grain bullet, that my bolt gun with a 1:12 will shoot.
Blain  [Member]
8/16/2011 4:37:20 PM
Wonder if the 62 grain fed fusion and 64 speer gold dots will be stabilized.
Nichonator  [Team Member]
8/16/2011 5:33:44 PM
My old Weatherby Vanguard 223 w/ 1-12" would shoot 55gr ammo all day at 200 to 400 yards and not tumble. Not very accurate but I could ring the 9" steel gong consistently.
FMJ  [Team Member]
8/18/2011 2:07:02 PM
Originally Posted By Blain:
Wonder if the 62 grain fed fusion and 64 speer gold dots will be stabilized.


I bet it will stablize the fusion 62gr load
orthodoxwarrior  [Member]
8/18/2011 4:05:30 PM
We had no luck at .223 and .222 velocity with 1-14 with anything but 50 or 55 grain bullets;with 1-12 up to 55 worked good.at 22/250 speed and 1-12 it was good with 60 or 65 grain;of course some barrels do better than others and of course different but we stuck with 50s in the .222 up to 55 in the .223 and mostly 55 in the 22/250 cause we were ground hog hunters anyway.Just cause you get a good group at a 100 yards does not mean you will at 200 or 300 either.Most .223 were 1-12 in bolt action and that has started tochange to 1-9 recently;with ar 15s now most are 1-9 or 1-7.I remember not so long ago every .223 was 1-12 almost and everybody shot 55 grain bullets.
wolfganggross  [Team Member]
8/18/2011 5:59:53 PM
Orginal M16 rifles had a twist of 1-14, but when the bullets wouldn't stablize in cold weather they switched to a 1-12 twist. With the adoption of the 62.5 grain heavy bullet they went to a 1-7 twist but a 1-9 will work. A 1-7 is needed for the M855a1 tracer. wolfgang
ehryk  [Member]
8/19/2011 4:42:52 AM
Originally Posted By wolfganggross:
Orginal M16 rifles had a twist of 1-14, but when the bullets wouldn't stablize in cold weather they switched to a 1-12 twist. With the adoption of the 62.5 grain heavy bullet they went to a 1-7 twist but a 1-9 will work. A 1-7 is needed for the M855a1 tracer. wolfgang


Ding! Perfect answer.
Blain  [Member]
8/19/2011 11:31:55 AM
That answer is wrong because twist rate has more to do with bullet length than weight. a 62 grain green tip is almost as long as most 69 grain bullets. A 62 grain soft point or fmj is not much longer than a M193 bullet.
ehryk  [Member]
8/19/2011 1:57:13 PM
but long enough. You are correct in that spin rate is indeed based off of the ratio of length vs. calliber. Overall, and in answer to the OP, he is absolutely correct.
wolfganggross  [Team Member]
8/19/2011 2:31:23 PM
It is true that the rate of twist will be generally be determined by the lenght of the bullet, which is why round nose bullets require a slower twist rate than spitzers of the same weight, and copper monolithics require a faster twist for the same weight. However, ogive taper, boat tail lengths, melpats, velocity and station pressure, plus other factors determine the ideal twist. Also with cold dense air, a faster twist is needed compared to warm air at high altitude.
1x7 technically too tight of a twist for any .224 bullet widely available, including the 80 gr. Manufactured orginally to stablize ss109 and or tracer ammo (m856), but further military testing has shown other twists to be superior (1x6 for tracer, 1x10 for SS109/m855). The military compromised on the 1x7. Some of the heavy custom stuff (87gr) may work well
1x8 great twists for 69-80 gr bullets (80gr Sierra needs a 1x8.2xxx twist)
1x9 good all around twist ratio, best suited for 52-69gr, but either end of the envelope will be questionable
1x10 practically the same as 1x9, but favors the lighter side a little more
1x12 great for the 40-52 gr bullets, 55gr will work but not the best. Most often found on bolt actions as thier primary use is varmiting
1x14 will understablize the .224 bullet
This all came from www.highroad.org "Barrel twist vs bullet weight", and from Mr Sattler, Law Enforment Sales Mgr and Archival Records Mgr of Olympic Arms

wolfgang
SecurityForcesmember  [Member]
8/19/2011 4:59:56 PM
A buddy shoots an SPS 1/12 twist and it won't stabilize 62 grain ammo of any type. I've personally had an LTR in 308 1/12 that wouldnt stabilize anything over 168 grain.

Its important to keep in mind that while the formulas for establishing the proper bullet weight/length to barrel twist combos are correct, there is an "unknown". That unknown is the barrel maker themselves. Not all rifles are "true" 1/12 or 1/9 etc etc. Some may be faster, some slower. Remington is NOTORIOUS for this. Easiest way to find out what your rifling really is is to measure it.
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