I have a brand new barrel from CMMG that came with an A2 flash hider, a thin washer, and a thicker washer with a ridge around the edge which I think might be called a crush washer.  How do I install the hider so that the vents line up vertically?

I've never used the thin washer.  I put the crush washer on bevel out (towards the end of the barrel) and then screw the FH on hand tight.  Then tighten it until it's lined up.  The guides at the top of the Build It Yourself page recommend 15-20 ft. lbs. of torque.  

peel washer (probably the thin one you got--usually silver): simply use a thin knife blade or screwdriver to remove the layers til the desired depth

crush: hand tight, then torque down until timed; narrow end is suppose to go towards the recieiver/touches the bbl, wide end/base towards the base of the muzzle device  bbl -<ll muzzle device

remember: to vice your bbl properly!

How do you vice your barrel if it's short?  Under the handguards?  And, what do I use to avoid marring it?

Quoted: How do you vice your barrel if it's short?  Under the handguards?  And, what do I use to avoid marring it?

its best to use a bbl vice block (or you can jury rig two pieces of wood to go around the bbl while you vice it) to secure the bbl while installing on muzzle devices

*taken from oly arms

marring can be avoided if you CLP the finish and cover it w/ leather wrapping

using just an upper reciever block is primarily for bbl installation; using it to install on muzzle devices can result in one canting the FSB by moving the bbl itself already attached to the reciever