I own a new bushmaster ar15 vmatch carbine and want to put on a new four rail handguard i just bought.  My question is how do i take off the old aluminum handguard.  It looks as though the gas tube goes through it where the barrel screws into the upper reciever, so unscrewing the handguard isn't possible, right? or would i have better luck letting my gunsmith do it for me.  thanks for the help

You'll either have to disassemblethe upper and front sight assembly yourself or have a gunsmith do it.  FF handguards usually require the barrel to be removed from the receiver and the front sight assembly/gas block to be removed as well.

The forward 3/4 of the tube can be unscrewed using a strap wrench, leaving the barrel nut on the receiver, which you'll need either a barrel vice (don't recommend it) or an upper receiver block (strongly recommend it), a vice, and an armorer's wrench to remove.  But if you have a front sight base with the front sight intact, good luck to ya, Bushmaster FSB is hard to remove.  So far the advice from folks that have successfully removed them (without cutting them open as I have done) is use an oversized drift punch, a big hammer and a bad attitude [:)]