Has anyone tried a purge with aerosol keyboard duster or another inert gas for eliminating first round pop?My Gemtech 5.56/223 suppressor is hearing safe with the exception of if used indoors. Outside or at the range (even with an over head cover) all you hear of the sonic crack is it going away from you. The crack is somewhat like a standard velocity 22LR but it does not ring your ears. I've measured the decibels and the decibel reading is less than 22LR. I shoot a Contender carbine and my AR all the time with it on and hearing protection is not needed. Might pick up more noise if at a range with overhead baffles in front of the line but that is the sound echoing off those.
With sub sonic we must remember the larger the diameter, the blunter the nose the louder the noise will be. Also remember it is the speed of the air moving over/around the bullet ogive that determines when it will 'crack. It is not the velocity of the bullet but rather the velocity of that air moving around the bullet nose. Also, sub sonic ammunition in handguns may exceed the when fired out of a rifle and can "crack". Most subsonic 300 BO load in 10" +/- barrels will "crack" when fired in 16 -20" barrels because of the velocity increase. Some 45 ACP with pushes 900 - 1000 fps out of my 5" M1911 and is very quiet with the suppressor on it will "crack" when fired in my 16 1/2" Rhineland conversion barrel because of the velocity increase.
To minimize "FRP - "first round 'pop'" with M21s with Sionics suppressors on them just before departing we would fire a round, leave the next round chambered and put a small "patch" of 90 mile an hour tape across the suppressor muzzle. That works well as the oxygen and cleaning solvent residue (the cause of FRP) is burned off inside the suppressor with that first shot. I have done the same when hunting with my own 5.56 and 30 cal suppressors and it seems to greatly minimize the FRP.