Ooh no! The USMC rifle is still the M40 except that its the M40
A4 model. The stock is still by McMillan. 
The debate on bolt action & semi-auto sniper rifle; technical
snipers prefer bolt action because of the follow-through action
when the trigger is pulled, which doesn't result in any extra
disturbance to the barrel.
Semi-autos sniper rifle are not bad, in fact, in some country the
M16 is being used as a semi-auto sniper rifle for the police force.
But semi-auto sniper rifles cost more, PSG-1 & its latest model
is in the highend cost range. US specOps still uses the refitted
M14/M21 semi-auto because they has a large surplus but they are
looking into some newer semi-auto sniper rifle.
For the .50 cal Barrett M82A1, there is a company, that offer sound
suppressors for tactical teams, Tac Ops. 