Please unravel the mystery of twist rate

[tmsand338]

Can someone tell me the relationship between twist rate and bullet size? Also if/how barrel length comes into play. I like the 62grn 5.56, but may start stockpiline 55grn .223 instead to save money. What twist rates are best for these bullets? I'd like to put an 18" barrel on this build, but will probably end up with a 16 incher.
Thanks.

[J]

Length doesn't affect stability nearly as much as twist rate.

The heavier the bullet, the faster the twist you want. Faster twist is a slower second number, which are read x_twists:x_inches. So a 1:7 twist does one full twist in 7 inches of barrel.

In you want to shoot 55&62, anything from a 1:7 - a 1:9 will likely be fine. I really like the 1:8 as I never go in to the 70's, but do go lighter.

My personal experience and opinion in general, which will not be the same for every bullet:

1:7 55gr and Up (77gr)
1:8 50gr - 69gr
1:9 40gr - 62gr
1:10 35gr - 55gr