need advice on twist rates for .223/5.56

[edmo01]

If you think you will be shooting bullets over 70 grains, get a 1-7" twist.

However, if you will be sticking to 55 grain bullets (like most of us), I suggest a 1-9" barrel. Depending on the individual barrel 1-9" twist rates can easily stabilize a bullet up to 69 grains and mine loves both 45 and 55 grain bullets.

Below are two groups at 100 yards while I was sighting in a scope. It is out of a 16" Colt heavy barrel with a 1-9" twist. The ammo is bulk Federal 55 grain FMJ.

Not bad accuracy from a barrel I bought in the mid-80s which has more than a few rounds through it. Although it isn't the latest military twist, it apparently spins them fast enough for 55 grain bullets and likes my handloads even better.

Edmo

 

[socalbeachbum]

wow edmo very nice.

when people speak of group size, is it measured center to center? so that caliber has no influence on the measurement?

so a MOA of .17 looks smaller than in .50 but the center to center is still MOA?

 

[Theohazard]

Yes, a group is technically supposed to be measured center to center.

 

[tuj]

77gr Fed. Gold Medal, 1:8 RRA upper, 20" bull barrel.

 

[Reloadron]

wow edmo very nice.

when people speak of group size, is it measured center to center? so that caliber has no influence on the measurement?

so a MOA of .17 looks smaller than in .50 but the center to center is still MOA?

Yes, hole center to hole center. However, sometimes the true hole center can be hard to see or use so you can measure edge to edge and the subtract one bullet diameter. So for example if I am shooting 308 Winchester and edge to edge of the two holes (furthest apart in my group) measures 1.000" using my calipers I would have 1.000 - .308 = 0.692" group size or roughly a 0.7" group.

For Internet posting I then take that 0.7" and automatically subtract an additional 50% and post I shot a 0.35" group. Just kidding on that 50%.

MOA (Minute of Angle) is just an angular measurement, one MOA is 1/60th of a degree, each degree in a circle consist of 60 minutes. That works out to be actually 1.047" at 100 yards but for simplicity we say 1 inch and drop the .047". So at 200, 300, 400, and so on the MOA would be 2", 3", 4" respectively. At 50 yards it would be 0.5".

Ron

 

[Dr.Rob]

I've never had 'spectacular' accuracy with any 55gr fmj commercial or M193 in my 1:7. Ditto for M855/SS109. None of it is loaded to push the accuracy from a rifle.

I have noticed: the 1:12 twist of an old Mini 14 even with a cold barrel throws wildly inconsistent patterns with bullets over 55gr.

I have fired 50 gr varmint handloads loads from a Colt 1:7 and an ER Shaw 1:9 with good accuracy--better than M193.

I finally bought some 77 gr match king bullets to see what sort of accuracy I might push out of my AR's.. and you can clearly see how much bearing surface there is on each bullet compared to a 55gr pill. Stabilized fast twist + more bearing surface SHOULD = more accuracy.

 

[Arizona_Mike]

1 in 8" will do everything . . . 70gr, 77gr, etc. You do not need 1 in 7" except for tracers. All the military designated marksman or sniper guns are between 1 in 7.7" and 1 in 8". They know what they are doing.

Mike

 

[Rugg_Ed]

I'll go with MistWolf

When people say "over stabilized" to describe a bullet that's spinning so fast it hurts accuracy, they are incorrect and are causing confusion. The more stable the bullet, the more predictable it's flight path. In other words, the more stable the bullet, the more accurate it flies.

Bullet weight has little to nothing to do with how fast it must spin to be stable. It's bullet length and shape. The longer the bullet, the more RPM needed to stabilize it. "But a longer bullet is always heavier", you say. No, that's not true. A bullet made from less dense material to the same size and shape will be lighter. Bullet shape also affects bullet length.

I shoot 22 Cal with 1 in 12, 1 in 10, and 1 in 9 twist rates each has preferred bullets that it likes best.

 

[sirgilligan]

I was doing some testing last fall with my .223 bolt gun with a 1:9 twist. It had no problems from 35 grain to 75 grain bullets, the 35 and 75 grain were Hornady Superformance.

These shots were resting on the hood of truck. There were six of us shooting my rifle that day and I didn't log who shot which. I do remember my Uncle shooting the 35 grain. The point is the 1:9 twist shot everything well and there were no keyholes or tumbling. We didn't take any particular time between shots, some consider the barrel to be hot on the majority of these.


This one isn't really a group. My Uncle just picked up the rifle and said he was going to shoot for the bulls eye. Don't mess with my uncle. ;-)








We were taking turns shooting the same target, these three are a group, ignore the other shot above, it was someone else shooting.