Redfisher60
Member
- Joined
- Jul 31, 2017
- Messages
- 70
In the AR world, is a 1/9 twist less expensive? I see from 1/7 to 1/9 twist in complete AR's.
Why would they choose 1/8 or 1/9 over 1/7?
Why would they choose 1/8 or 1/9 over 1/7?
Seems like they started with 14 and quickly changed to 12 but I'm not certain. ... This instability lead to poor performance at longer ranges.
the alleged .303 Mark VII tendency for the bullet to "settle down" and become more accurate at longer range than it appears when fired at shorter ranges.
The varmint rifle 14 twist was found not adequate to stabilize cheap 55 grain boattail FMJ in cold dense air. Nothing to do with lethality in the tropics. So they went to the 12 twist.
The USMC rifle team built some 10 twist rifles with the first free float handguards to squeeze the most out of the 55 gr M193.
After that, it was a continual process of longer/heavier bullets and the faster twists needed.
The 9 twist and the 68-69 grain bullets seem to have come along hand in hand.
And as said, a 9 twist is fine for the M855/SS109 but it takes a 7 twist for the very long tracer.
Target shooters seem to have settled down with 7.5-8 twist and 80 grain bullets for 600 yards. Magazine length 77 grain for shorter ranges.
I have a 6.5 twist barrel for 90 grain boattails but that seems to be a dead end.
Redfisher60 wrote:
Why would they choose 1/8 or 1/9 over 1/7?
Not in the 5.56/2231/7 is well known to blow up 55gr bullets at full speed
(1/7 is well known to blow up 55gr bullets at full speed) its a good all around number.
That's an interesting chart, but it doesn't account for the < 2 MOA groups I get from 1:9 with 75 and 77 (by about 3.5 or better MOA).You may want to look into this research.
https://plus.google.com/+LuckyGunner/posts/ZZPNiRXyqYm
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In the AR world, is a 1/9 twist less expensive? I see from 1/7 to 1/9 twist in complete AR's.
Why would they choose 1/8 or 1/9 over 1/7?
Not in the 5.56/223
may do fine out of a 14', may do fine with heavy jackets, but I have personally seen 55's explode into dust at the 75 yard mark with enough consistantcy to demonstrate for other people, and its not exactly an unheard of thing. You can find THR posts about it. I was chronoing 55 grain bullets at about 3300 FPS at the time and was keeping them in 2' at 50, and off paper, at 100. Looking out between the two you could see puffs of smoke about 4 feet up, 75 or so yards out when the rifle fired. Its was a neat thing to see. Im sure military bullets would be fine even at the speed because the specify jacket material and dimensions. Commercial bullets (especially the cheap ones I saw this happen with) are looser. I agree the military specifies to avoid them in the A2 because of accuracy/wear.I've never seen a 55 grain "blow up" in a 1:7. I fire them regularly through my multiple 1:7 carbines and have had nothing but consistent performance from a number of manufacturers. In addition, one of the advanced shooting schools I attended at Ft Bragg exclusively uses 55 grain M193 through standard issue 14.5" M4 carbines, and they literally fire millions of rounds of this stuff, with engagements out to 300 meters. I believe they use that round in order to minimize wear and tear on steel targets. Never saw or heard of this happening there.
https://www.thehighroad.org/index.php?threads/are-my-bullets-disintegrating-in-flight.821778/ this is what I found on the subject without looking, and while 52gr is not 55gr, its fairly close, and he's also producing velocity well below the max for a 55. I had numerous 55's explode out of a 1 in 7 using commercial bullets. 1 in 9 did fine. I think military bullets would be fine, but military 55gr bullets are not exactly the standard.Not in the 5.56/223