Thread: Twist Rate:Projectile Weight

Sako 30 cals (308 and 3006) are 1-11.
Mate has a winchester 70 (for a while I had it in my head it was a remmy) with a 1-13. 300 win mag, bloody waste.
Took a metric shit ton of powder and projectiles trying to get it to group with the heavier projectiles. Measured the twist and found the drama. Went to 155s used in the Palma match and instantly came good.
He has found a 178 that will work just.
He has been talking to the guy that had it built and he has done it again. 300 mag case with a 1-13 twist. Bit dumb really.

Originally Posted by Rn-85

For example, I've been told 165gr is too heavy for my 1:11 308.

That's exactly how I've been shooting lately (Sako factory ammunition). Accurate.

Originally Posted by No.3

Well, it kinda is - the light-for-length mono copper bullets need a very fast twist for weight to make em fly straight... But yes, there's a little more to it than that although for the most part that's the gist.

I'm not sure what part of what I said you think isn't quite right this time?

This thread jogged my memory of a short-lived cartridge the Spanish tried in the 50's. 7.92x41 CETME with an absurdly long aluminium bullet with a copper band: https://www.youtube.com/watch?v=3Njddshr3n8

And yes, the JBM stability calculator reckons this light-for-length bullet needs about a 1:5.5" twist. Making it heavier increases the stability. Although I don't know whether the unusual mass distribution of the bullet breaks the formula and what the actual twist rates used were.

Don't forget atmospheric density (altitude, temperature, and humidity) affects stability as well. Also a marginally stabilised projectile can shoot well but will have a reduced B.C.

Originally Posted by Pommy

I'm not sure what part of what I said you think isn't quite right this time?

Ha, thats what I was thinking as well...