Short/lite bullets on fast twist rates barrels

[civilian75]

Shooting 55gr or lighter bullets on a 1:8 twist barrel

I own a M4 with a 1:7, and plan to buy something like a RRA LAR-15 Varmint A4 (Wylde chamber) with a 1:8 twist. I have observed for a 1:8 twist, optimum bullet weights range from 67 to 75 gr. But, I bet there are lighter/shorter bullets that can shoot sub-MOA on a 1:8 bbl. If you have had such an experience, I'd like to hear about it. Please, specify as much as you can about your rifle, bullet/cartridge (factory v. handload), muzzle velocities, and of course accuracy @ distance, etc.

 

[civilian75]

err... anyone?

 

[Jim Watson]

Problem is, I don't have a 1:8. In a narrower range, I have a 1:9 that is more accurate with 52 gr bullets than anything heavier and a 1:12 that is more accurate with the 60 gr bullets that are as long as it will stablize.

My 1:6.5 is as accurate with 75 gr A-max as it is with the 90 gr SMK I bought it for. But if I want to shoot beyond 600 yards, I had better feed it 90 gr VLDs.

Unless you are working at the cutting edge of very heavy bullets for long range, very light fast bullets to blow up varmints, or grinding out that last .01" in benchrest matches, I think rifling twist rates are overstudied and overemphasized. There is a lot more flexibility there than many folks think.

 

[Pokyman]

I am of the opinion that specific twist rates are very important for bullet stabilization. That may seem like a dumb statement, but bullet accuracy suffers if shot out of a barrel that has a twist that is too fast for the length of the bullet as well as too slow.

I owned a 219 Zipper Improved (performance about like a 225 Winchester) with a 14 twist barrel that would shoot 55 grain bullets at a velocity of ~3350fps. 5 shot groups were consistently 5/8 inch or better.
I had the chance to sell the rifle. I had a bad case of sellers remorse. Since I had everything except a rifle, I built another one. I built this rifle with a 12 twist. Same ammo and load was used in the tighter twist. Chronographed 3320 fps. average. Accuracy with 55 gr. bullets is ~1". I tried 60 gr. bullets. Group size averages 3/4" with an occasional group at 5/8". I haven't tried heavier (longer) bullets yet, but expect even better accuracy with boat tail bullets in the 60 gr. area.
I have a 22 K Hornet with a 14 twist. Load data as follows: Velocities chronographed by me.

40 Gr. bullet 13 Gr. Lil Gun velocity 3283. 5 shot group 3" avg.
45 gr H.P. 9 (bullet designed for Hornet- that means it is fairly short)
11 Gr. Lil Gun 2800fps. 5 shot group 1 1/2 "

45 gr. Soft point 11 gr. Lil Gun 2772 fps. 5 shot group 7/8"

50 gr. Hollow Point.
8 gr. Lil Gun (mild load) 2160 fps. 5 shot group 5/8 goup.

22 6MM Ackley Improved. I call it my AT&T rifle. Just in case you want to reach out and touch something.

Krieger 8 twist.

44 gr. RL 22 75 gr. A Max. 3420 fps. 3/8 to 1/2 groups consistently.
44 gr. RL 22 80 gr. Sierra Match King 3390 fps. 3/8 to 1/2 groups.

I have another 22 6MM Ackley Improved with a Krieger 7 twist barrel.

44 gr. RL 22 75 Gr. A Max 3350 fps. 5/8 group avg.
44 gr. Rl 22 80 gr. Sierra Match King. 3320 3/8 to 1/2" groups.

While over spinning a bullet is not as critical as underspinning, shooting bullets out of fast twist barrels requires carefull consideration of bullet length if you want top accuracy.

 

[Float Pilot]

When our units went to the 1 in 7 twist M16A2s and the M249 Saws which also have the 1 in 7 twist, we still had tons and tons of the old 55 grain ammo.

So we were told to use that for qualifications and match shooting.... Including a huge supply of the old style tracers.

The 55 grains bullets were developed in a 1 in 14 twist and then the Army latter settled on the 1 in 12 twist.

However, that shorter, lighter-bulleted ammo worked just fine in the 1 in 7 twist weapons.

I even fired a M249 SAW at 700 meters during a match using the 55 grain stuff and other than some slight signs of bullet yawing at that extreme range, I was still hitting the targets.

 

[Pokyman]

To continue with my train of thought.
If I were to err with twist rate, I would err on the side of faster twist.
One area of the accuracy issue that rarely gets proper consideration is bullet structure and design. If one does the math, it is amazing how fast bullets are rotating. Driving bullets at high velocities with high rates of spin puts an unbelievable rotational stress on bullets. Some bullets will deform or fly apart because of these stresses.
I built my 22 6MM IMP with the 7" twist to specifically shoot the Berger 90 gr. VLD.
I was disappointed to find out that even though the VLD is designed to use in 7" twist barrels that this bullet will not withstand the rotational force excerted on it being shot at high velocity.
I can't tell you how accurate this bullet is because they never reached the target. Even at 25 yards. When I say they never reached the target, I shot almost 50 rounds at the 25 yard target. I tried various powders and velocities. After the initial trail I did not try and chronograph. I was not happy that my chrono looked like it had been shot by a shotgun.


I wanted to see how well a 52 gr. bullet would group out of my 22 6MM IMP with an 8" twist barrel. Because of my previous experience with the Bergers I did not chronograph. Out of 5 shots only two hit the target at 100 yds. One key holed and the other was in the X ring. The target was 4' X 4'.

Now, after all I have said, let me say that bullets driven at reasonal velocities will shoot just fine out of standard or fast twist barrels. Short bullets shot out of fast twist barrels may not shoot as well as longer ones.

I realize that this is a lot more info than you had asked for, however the advice and data were free.

 

[Haxby]

Jim Watson said "rifling twist rates are overstudied and overemphasized."
I agree.

 

[gdcpony]

I wondered the same thing. Here you go.
http://www.thehighroad.org/showthread.php?t=564355
http://www.thehighroad.org/showthread.php?t=507874
1:9 but should help you out.

 

[Dr T]

One issue with fast twist rates and light bullets. Some of the light bullets are quite frangible with very thin jackets. They may disintegrate due to the rapid rotation. At 3300 fps, the little guys are spinning at about 340,000 rpm.

 

[joed]

I had a 1:9 Savage. Mine shot the 69 gr match bullets into 1 ragged hole. 50 gr bullets were 3/4". I tried 40 gr and best was 1".

I've always had the opinion the twist determines what weight bullet will be accurate and my shooting showed it. At least in my gun.

Now someone else will probably say they shot the 40 gr in a 1:7 and got great accuracy. I'd have to see it to believe it.

 

[Tim the student]

I have a 1:8 RRA. It shoots 50g on up very well. I haven't tried anything lower, other than the 36g Varmint Grenades, which are extremely long for weight.

 

[Jim Watson]

I built my 22 6MM IMP with the 7" twist to specifically shoot the Berger 90 gr. VLD.
I was disappointed to find out that even though the VLD is designed to use in 7" twist barrels that this bullet will not withstand the rotational force excerted on it being shot at high velocity.

I have a .223 with 6.5" twist as recommended by Sierra for their 90 gr MK.
It does fine if loaded to the rather mild Sierra specs. But it took heavy loads to get enough muzzle velocity to remain supersonic at 1000 yards. When I got to that point, I started losing bullets on the way to the target. If they didn't fail they were accurate; I had one string that was nothing but Xs, 10s, and misses. I tried this and that with powders and OAL but never did get it to work. I actually caught a couple of imprints of BENT bullets on paper at 100 yards.
However, my .223 will shoot VLDs satisfactorily. I use mostly JLKs but the few Bergers I shod did ok, too. I guess that .22x6mm just drives them that much harder.

My rifle will shoot 75 gr A-max accurately if not loaded so heavy as to spin them apart. So I use them and Sierras at bearable velocities at 600 yards. When I want to stretch the .223 to 1000, it gets JLKs.

 

[civilian75]

Thank you all for the feedback. It is all excellent. There is something to learn from each one. It is never too much. I appreciate you taking the time.

I have a 1:8 RRA. It shoots 50g on up very well. I haven't tried anything lower, other than the 36g Varmint Grenades, which are extremely long for weight.

Tim, since you own the platform I have my eyes on, I would appreciate you elaborate as much as you can.

 

[Tim the student]

I have a 20" Varmint EOP. I use it for paper mostly, and once a year prairie dogs.

The gun shoots 50 and 55g bullets really well. The only thing that won't shoot MOA or better are FMJ's. I rarely shoot those, but I without looking at my notes, I think I am better than 2 MOA with the best load I have found so far with those (which isn't much experimenting).

I predominately handload for it, and I don't really remember the last factory loads I put through it.

I really only load up 50-55g for it - very rarely anything heavier. My preferred powders are 8208 and Benchmark. I have had good results with others too, but I like those two the best.

As you might expect, it usually likes loads that are in the middle of the spectrum - no compressed charges for me. I'd need to go look at my notes for velocities. I can do that tomorrow.

Is there any other info you would like?