barrels with different twists

[dirksterG30]

Can someone give me the lowdown on what the different rate of twists on AR-15 barrels? From what I've read, it seems that the different twists were to accomodate different types of ammo. The Rock River Arms models I am interested in have a 1:9 twist. Also, are there disadvantages to this twist?

[RMTactical]

http://www.ammo-oracle.com/body.htm

[switch625]

I beleive just about every AR is 1:9 nowadays. Getting a different twist would take some looking and cost more. Some of the fellas on arfcom like the 1:7, not sure why. Unless you have specific ammo or a special purpose just get a 1:9, shoot it and join the fun.

[G37 Commando]

I would go with the 1:7 if you intend on shooting only 62gr and heavier bullets, especially the 77gr type stuff.