I plan to do bench shooting and prone position shooting - what size mag should I use? I've heard that the 30rd mag sticks into the ground... so that leaves the BATF approved 10rd and 5rd mags, or the 20rd.

I want something that is built in accordance with mil-spec and can be taken apart to be cleaned, etc... but also fitting my need to shoot on a bench or in the prone position.

Where are some places that I should go to buy quality versions of the recommended mag? I'm an AR15 newbie so please bear with me?

The 20s are great for the bench and prone. 30rd mags are fine for everything else. USGI mags are good, especially if they still have the alloy follower.
Check the EE (Equiptment Exchange) here or you might try CMMG (also on the EE)

Quoted: The 20s are great for the bench and prone. 30rd mags are fine for everything else. USGI mags are good, especially if they still have the alloy follower. Check the EE (Equiptment Exchange) here or you might try CMMG (also on the EE)

+1 20's work great, at leat the old style ones.  I don't know about the new cut down 30rounders.

I ordered some 20's from CMMG for $18, they got shipped out today.

-Tyler

I ordered the 20rd straight mil-spec mags... are those the ones you ordered?