rifling?

[munky]

When rifling is being talked about on a barrel, example. 1:12 or 1:7 what does this mean? Is it 1 rev. every 12" ? I know it has to do with the twist. what is a good or super accurate twist ratio?

Thank you

 

[manitou210]

1: 12 is like you mentioned one revolution in 12"
Best for accuracy depends on caliber and size of bullet you would what to shoot.
A .223 Rem with a 1:14 twist would not stablize heavy bullets like 80gr but a
1:8 or 1:7 would work well, but if you only want to shoot say 52gr the 1;14 would be great.
hope this helps

 

[mooncoon]

there is a formula called the greenhill formula which gives the minimum rate of twist to stabilize a given bullet. Normally you would use a rate of 1" faster than the formula recommends.
twist =150 x diam squared over length and you can interchange twist and length to figure out the maximum length a twist will stabilize

cheers mooncoon

 

[Woodsman]

h t t p ://en.wikipedia.org/wiki/Rifling

 

[sunray]

"...Is it 1 rev. every 12"?..." Yep.
"...what is a good or super accurate twist ratio?..." Depends on the cartridge and the bullet weight. There is no one rifling twist that covers all cartridges or bullet weights.
Heavy bullets for a given calibre tend to prefer a faster twist. "Heavy" for, say a .223, starts at about 60 grains. For a .243 it's at 85 grains. .30 calibres work well with a 1 in 10 twist and really like 165 and 168 grain bullets. Like manitou210 says, it has to do with stabilizing the bullet.