Range Report Bullet Stability Trade-Offs

[BamaAl]

So, I've been doing a bit of reading ( a dangerous thing I grant you) and a couple of inconsistencies have popped up. In 308 for example it appears that faster twist rates provide greater stability across the board. 1:10 for example seems to show the best stability across the board from 155 palma to heavy suckers.. But, I also read about many shooters choosing a slower twist rate, 1:11.25 seems to be pretty common. Soooo, what am I missing? They are trading off stability for something but I'm just not sure what. Is it possible that they are loading hot and the slower twist rate is less likely to yank the jacket off the bullet?

 

[GlockandRoll]

Re: Bullet Stability Trade-Offs

All things being equal, it is commonly accepted that faster twist rates (at the same BBL length) will stabilize heavier bullets.

let's say for example you have a 20" 308, and you wanted to stablize 175's, you could probably do that with a 10 twist. However if you wanted to go for a longer BBL for increased velocity, you could probalby shoot a 12" twist if it were 24-26".

The 11.25" twist the M40 uses with 5R rifling seems to have struck a sweet spot and I'm very happy with my 24" FN SPR that has 5 groove rifling and a 12" twist. It really sings with the 175's at a faster velocity than anticipated. NO problems getting to 1K with 44.5 grains of varget and I anticipate (as it's a 12" twist) that I'll be able to push the 155 scenars allong rather nicely. Assuming I can get velocities around 2900fps.

 

[tobias]

Re: Bullet Stability Trade-Offs

It's really a trade off. There are several effects due to spin that have an influence on accuracy. For example lateral throwoff increases with higher spin. Some Bench Rest shooters even accept a small instability...

 

[GlockandRoll]

Re: Bullet Stability Trade-Offs

I'm interested in progressive twist rates like the FN Balista.. cant wait to get my hands on one of those.

 

[okiefired]

Re: Bullet Stability Trade-Offs

Dosn't have as much to do with weight as it does with length of the bullet. Palma style bullets are very long therefore it takes a faster twist to stabilize them as it does the "heavies" that are also longer simply because of thier increased weight in the same bore.

okie