How much heavier of a projectile will a 1 in 12 twist handle, if any, as compared to the more standard 1 in 14 twist rate? Thanks for any help.

Its not the weight that determines twist as much as the construction of the bullet.
total length, nose length boat tail length and diameter.
also velocity is a factor out over 600yrds,.
from 3500f/s out to 4000 f/s a 11.4 to 11.5 twist is specified.

quote:

Originally posted by Leo M:
How much heavier of a projectile will a 1 in 12 twist handle, if any, as compared to the more standard 1 in 14 twist rate? Thanks for any help.

My 22-250 has a 12 twist and really likes WW 64 gr pills.

My 12" twist .22-250 shoots 60 grain spitzers nicely, down to ~3300 FPS muzzle velocity.

let me clear that up for you here's an example..
Gunsmiths generally use the Greenhill Formula to determine the optimal twist for a given bullet. The formula is T=150(d/r) for velocities from about 1500 to 2800 fps. Substitute 180 for the 150 value for velocities exceeding 2800 fps. "T" is the twist rate. "d" is the bullet diameter. "r" is the bullet length to diameter ratio (length of bullet divided by diameter). In .308, it works out fairly well. Sierra 168 grain Matchking is 0.308 inches in diameter. Bullet length is about 1.210 inches so we have a length to diameter ratio of 3.929. Plugging this value into the formula and using the 150 constant (the proven best velocity for the 168 grain MK is 2550 - 2600 fps), we get T=150 x (.308/3.929); T=150 x 0.078; T=11.76 inches or 11 3/4 inch twist …. One rotation of the bullet for every 11.76 inches of barrel traveled. This is very, very close to the "standard" 12 twist barrels. one of the reasons they shoot the 168s so well. The 175 Matchkings do not perform as well in the 12 twist barrels. Again diameter is 0.308 inches. Bullet length is 1.257 inches, resulting in an ld ratio of 4.081. … plugging into formula (optimal velocity is 2500 to 2550 fps so we will use the 150 constant again) T = 150 x (.308/4.081); T = 150 x 0.0755; T = 11.320. That approximate half inch twist difference makes a big difference . 12 twist barrels tolerate 175s but do not excel with them. The general rule of thumb is to use the fastest twist you can tolerate and match to the longest bullet (usually heaviest) you intend to use for the life of the barrel