Twist & 223 Remington...

[BCB]

First, before I get accused of being lazy, I did searches for a formula to help determine twist at certain velocities. I searched “223” as that is the caliber I am interested in and I searched “twist”…

I got hundreds of hits, but I could not find the equation someone posted a link to yesterday…

It was an equation (spreadsheet) to calculate approximate twist…

I did a 223 project about half-dozen years ago and it was pretty miserable. I was using a T/C 14”…

In that amount of time, I have learned considerable about shooting cast from this website and I thought I might just try it again…

Anyhow, the T/C has a 1-14 twist and I was going to check which boolits that I have (given to me by several members of this site when I first started the project)…

225646…225415…22596…225450…22-55-SP

Any help on a link to that spreadsheet?...

Thanks…BCB

[Larry Gibson]

I'm not familiar with the 22596 but of the others the 225646 will probably give the best accuracy at higher velocity. The 225415 and the 22-55-SP will probably do about equal. All will do fine in a 14" twist, better than in a faster 7-12" twist for sure.

Larry Gibson

[buyobuyo]

Here is an online calculator. http://www.jbmballistics.com/cgi-bin/jbmdrag-5.1.cgi

[BCB]

I'm not familiar with the 22596 but of the others the 225646 will probably give the best accuracy at higher velocity. The 225415 and the 22-55-SP will probably do about equal. All will do fine in a 14" twist, better than in a faster 7-12" twist for sure.

Larry Gibson

Actually, the 225646 is the heaviest. I was uncertain of that one as it weighs in at around 62 grains with the check in place. I don't know what velocity I am going to try to achieve. I would basically just like a round that would hit 12-ounce cans at 100 yards with very good consistency...

I know the 16" barrel that I have will shoot 1.25" groups at 200 yards much of the time with J bullets. The 14" that I have also was nearly as good of a shooter. Both were with 50 grain J bullets. Both have Burris 4x-12x 'scopes on them so seeing the target at those ranges is not a problem. Yet, with the cast some years back, I was only shooting around 2" at 100 yards. Sometimes a bit bigger. I wonder if I am expecting too much to try to get ≤ 1.5" at 100 yards?...

buyobuyo...

I will mess with that website and see if I can come up with some data that might help push me in the correct direction...

Thanks to all...

BCB

[Larry Gibson]

Cast bullets are generally shorter than an equal weight jacketed bullet. Proper stabilization is dependent on the length of the bullet and velocity of a given caliber, not the weight. If the 225646 is the same length of shorter than the J bullets that give you accuracy then it should stabilize quite well enough, especially at the "higher velocity" I mentioned.

Meaure the length of your bullets and run the equations projecting a reasonable velocity or the lowest you expect to shoot at. The answer (minimal twist needed) will give you an answer but only the gun, bullet and load will give you the correct answer. Also the faster you push the bullet the slower the twist can be within reason.

Larry Gibson

[oldpapps]

Here is the formula that I use:
Sg=(30*C5)/((C7/C4)^2*C4^3*C6/C4*(1+(C6/C4)^2))*(C8/2800)^(1/3)*((C9+460)/(59+460)*29.92/C10)
Where:
Sg - is the stability coefficient and should not be less than 1.4, but more is ok
C4 - Caliber in inches (.223 for both .222 and .223)
C5 - Bullet Weight in grains
C6 - Bullet Length in inches
C7 - Barrel Twist in inches per turn
C8 - Muzzle Velocity in fps
C9 - Temperature in degrees F (59F normally used)
C10 - Pressure in inches of mercury (29.92 normally used)

If the variables are plugged into a spreadsheet in the 'C' column at the appropriate row, the stability coefficient appears in the formula cell.

Remember, these numbers are only generalities.

Enjoy,

OSOK