Fun stuff but annoying: thanks to the design of M-16, the gas system funnels ammonia gas straight into the shooter’s face thanks to the back pressure from the suppressor. Dang thing asphyxiates the firer, which makes aiming a problem.
A few options are available to manage gas blowback with a suppressor:
Adjustable gas blocks:
The W.A.R. upper by Innovative Arms which has a suppressor setting:
And the PRI Gas Buster charging handle.
Each of these individually can significantly reduce gas blowback into the shooter's face when using a suppressor. Combine either of the first two with the charging handle and you should be able to lower blowback to unsuppressed levels.