38-55 twist

[letfly]

Hi All, what would be the optimum twist rate for a 1.312 '' postell bullet at 335 gr. in a 38-55 at 1100 fps. Seem to be having stability problems at 625 yards. Thanks.

[SchuetzenDave]

The gyroscopic stability programs indicate a maximum length of bullet for my 18:1 twist barrel is 310 grains.
The Sg for a 325 grain in a 18:1 twist barrel is 1.37 (not enough spin).
Therefore for a longer heavier bullet a 16:1 twist would be more appropriate.


Caliber 0.378 Inches
Bullet Weight 325 Grains
Bullet Length 1.312 Inches
Barrel Twist 16 Inches/turn
muzzle velocity 1100 fps
Temperature 50 degrees Fahrenheit (59 is standard)
Pressure 29.92 inches of mercury (29.92 is standard)

Sg = 1.60

Sg shouldn't be less than 1.4. If Sg is greater than about 2.0, you may gain some accuracy by going to a slower twist barrel.

[SchuetzenDave]

The gyroscopic stability programs indicate a maximum length of bullet for my 18:1 twist barrel is 310 grains.
The Sg for a 325 grain bullet in a 18:1 twist barrel is 1.37 (not enough spin).
Therefore for a longer heavier 335 grain bullet a 16:1 twist would be more appropriate.


Caliber 0.378 Inches
Bullet Weight 335 Grains
Bullet Length 1.312 Inches
Barrel Twist 16 Inches/turn
muzzle velocity 1100 fps
Temperature 50 degrees Fahrenheit (59 is standard)
Pressure 29.92 inches of mercury (29.92 is standard)

Sg = 1.65

Sg shouldn't be less than 1.4. If Sg is greater than about 2.0, you may gain some accuracy by going to a slower twist barrel.

[letfly]

Hello Dave, the twist is 14. The load is #2 alloy. 335 lyman, 40 gr. Swiss 2F light compression, .030 veg wad ,BR-2, winchester case. The thing is that it shoots well with the 20.5 grain load of H4198 in the back of Dells book 'modern schuetzen rifle'. The 360 buffalo arms money bullet is sideways at 625 yards. ??? I would give up on this barrel if it didnt shoot so well with smokeless. It is a green mountian on a Higgenbotham roller. Thank you for your time

[SchuetzenDave]

Shooting only 1100 fps past 500 yards results in too much drag before it reaches the target.

You need to increase your velocities.

I was shooting 20:1 alloy bullets with 50 grains of Swiss FFFg in my .38-55 to get her to stay flat out to long distances.

14:1 twist will work well with your 335 bullet out to long distances if you increase your velocities to ensure you overcome the affects of too much drag that affects stability over long distances.

[letfly]

Thanks for the reply. Best way to increase vel. with black?

[letfly]

looks like i will need a compression die!

[SchuetzenDave]

Compress the powder.
Swiss FFFg will increase velocities up to 10% more than coarser BP plus Swiss is a bit stronger powder than many other makers BP.
Use a tapered bullet so you can extend it out further into the barrel and put more powder in your case.
Does not matter if your grease grooves are exposed as long as your base band has good tension in the case mouth.

[letfly]

Dave, can you suggest a bullet?

[SchuetzenDave]

With your 14:1 twist I would use the BACO 345 grain Tapered Creedmoor JIM378345CT .378" nominal diameter 1.33" overall length and 0.700" bearing surface length.

The Creedmoor has a better center of gravity with less nose angle deflection (less susceptible to wind drift) and is really good for long distance shooting.

For long distance shooting we like to over spin it (Sg>2.0) to compensate for drag over longer distances.

Caliber 0.378 Inches
Bullet Weight 345 Grains
Bullet Length 1.33 Inches
Barrel Twist 14 Inches/turn
muzzle velocity 1250 fps
Temperature 50 degrees Fahrenheit (59 is standard)
Pressure 29.92 inches of mercury (29.92 is standard)

Sg = 2.23

[letfly]

Thank you. will order bullet mold, 3F & compression die Monday.

[marlinman93]

I own and shoot a Schoyen barreled Ballard in .38-55 and the Schoyen is a 1:15" twist. I shoot a 320 grain tapered bullet in it, and it is extremely accurate with that bullet.

[letfly]

is the mold for your bullet available?

[beltfed]

JIM371310E.jpg

How about this Dual Diameter Elliptical Paper Patch bullet that will work in your barrel to 600 or more and
you can seat it out for more powder/velocity as others have suggested.
beltfed/arnie

[letfly]

Hello Beltfed, any particular mold in mind? I have not PP before, but as the ends justify the means ....