How can i tell

[battleship]

if my AR barrel has a 1 in 7 twist or a 1 in 9 twist etc etc, the barrel is chambered for the 7.62x39mm caliber, to be honest i dont realy know what that twist ratio means, anyone can educate me on this, thanks.

[postal]

1-7 means the rifling in the barrel makes 1 complete spin (360) for 7 inches of length.

To measure, use a cleaning rod with a tight fitting patch on a jag. Put the rod into the barrel a few inches. mark a spot on the rod about to enter the chamber- Slowly push the rod down the barrel watching for the rod to make 1 full revolution (another mark on the rod- to watch the spin helps), and stop at 1 complete revolution.. Mark the rod right next to the chamber- take the rod out, and measure the length between the first and 2nd mark- this is the length for a full revolution.

edit- rifling is to spin the bullet to stabilize it just like a good spiral throw on a football. The rate of twist will influence the best bullet weights to be fired from that barrel. For 30 cal, for example, a 1-10 twist is often the best choice because it will stabilize *almost* all weights of bullets common to a 30 cal round.