While there should be clearance between the hand guard and gas cylinder, the guard should fit tightly enough in the lower band so it cannot move back and forth. This movement can increase the size of the bullet groups on target, and should be eliminated.

Brownell's Acraglas kit
Masking Tape
Screwdriver or punch
File or #100 grit sandpaper
Front handguard
Lower band

Brush 2 coats of Brownell's Release Agent on the lower band, letting dry 6 hours after each coat.
Put the lower band on the hand guard. Be sure to press the band on as far as it will go.
Wrap masking tape around the inside and outside of the hand guard.
Press on the tape with your fingernail so it seals tightly. Be sure to do the inside,too.
Set the guard on its nose.

Mix the Acraglas using the Brownell's instructions.
Pour Acraglas into the area where the hand guard lip fits into the lower band.
Use enough Acraglas to bring it up to the top of the lip, but don't cover it. Too much will interfere with the lip of the rear handguard fitting in the lower band.
Check for Acraglas leaks every 15 minutes for 2 hours after pouring the Glas in, and apply more tape/pressure so the Glas doesn't leak out.
Let the assembly dry overnight.

The next day, peel off the masking tape.
There will be no movement of the hand guard within the lower band.You may want to make the hand guard and lower band separable without tools.
Use the hammer and screwdriver or punch to tap on and separate the hand guard and lower band.
Remove the release agent from the lower band.
Use the sandpaper to sand the outside of the guard where the new Acraglas is, and test fit the band until you can put the band on and remove it by hand. It should still fit tightly enough so it won't move back and forth when assembled on thrife.

After putting the rifle back together, make sure there is clearance between the gas cylinder and front hand guard by sliding a piece of telephone book cover between them.
If somehow the lower band wasn't on the whole way before putting the masking tape on, you'll have to file some of the Acraglas off the back of the guard so it fits correctly.