Members,

What differences in penetration and/or stabilization would you expect to see in a 458 barrel, firing a 480 grain bullet at 2150fps, between a 1 in 10 twist and a 1 in 18 twist? What are the advantages and disadvantages of both rates of twist?

Perry

Perry,

The way I understand it, in theory at least, you should be able to get better penetration with a faster twist, but you might get lower velocity.

A 20 inch twist is sufficient to stablize a 480 gr bullet as far as accuracy is concerned while an increased rate of twist is to ensure stabilty after impact as Saeed has suggested. The fastest 458 I have ever seen was just under a 13 twist. 14 is more or less standard for the 458 and is absolutely sufficient. Regards, Bill.

There were some threads regarding this some time ago. Search under "Superpenetrator".

I wonder if a 1:10 twist will do for anything, any caliber, except maybe weak varmint type bullets at top speed.

Hermann

there are tons of recoil calculators out there, and it does make a diff. In short, if you use heavy for caliber bullets, the faster twist stabilizes the longer bullets, see 244 rem vs 6mm rem. This also applies to larger bores. A 358 in 1-18 (35 rem twist) will NOT shoot 250 gr rn, or 225 spbt bullets worth a crap.
also, you can have a pressure issue with a faster twist. the twist acts like "threads", and a faster twist, in the same bullet, WILL have higher pressure, all else being equal. Take the 358 for example, again, the higher pressure might be a good thing, as the case doesnt have a large capacity. I've got a couple 358s, and in the same maker barrel (okay, let's not delve into THOSE details) with different twists, I get different vels. And, contrary to popular believe, SOMETIMES faster twist give faster vel. It's purely due to case capacity and pressure. the 1-10 give me ~65fps faster (long string of averages) than the 1-12. It's also more accuarate.

go figure.
jeffe

Thanks guys.

Perry

I just read an article on the net that explained the rifling story. I thought I saved it but I can't find it. It explained how too much twist was very bad, just as to little is but in a different way.
The following site has a ton of good info and I believe it was a link I followed from the rifling info site so maybe check its links?
"http://home.sprynet.com/~frfrog/froghome.htm".

Btw, go there and click; "Miscellaneous Questions and Answers", there is a ton of cool info. I found the following formula under;
"Q: How do you determine the rifling twist needed to stabilize a given bullet?"

There is an old formula called the Greenhill Formula that, while it was designed for estimating twists for boat tailed lead core bullets of moderate velocity, does a pretty good job of estimating twist required for flat based bullets under "normal" conditions.
T = Twist in inches
K = Greenhill's constant = 150 (This has to do with the specific gravity of a jacketed lead bullet)
D = Bullet diameter in inches
L = Bullet length in inches

T = (K * D2) / L