On a semi auto rifle, gas or blow back, the bolt velocity will be increased. The reason the empties were flung further and crud blows back into the action. The suppressor, like an automotive muffler will create back pressure restricingt gasses that normally blow forward out the bore and increase pressure - blowing back the bolt harder, or in a gas operated gun (ie: M4's with suppressors) increasing port pressure in the pressure of the gas and cylinder systems. Military guns require significant mods if they are going to be used suppressed for duty. May want to keep an eye on the buffer. AC