Timmies use about 70 psi to drive the ram back and forth. The reciprocating mass is relatively light, also, I guess about 50 grams. In a blowback, the same air that is propelling the balls is driving the hammer back to latch on the sear. That means cocking pressure is about 850 psi. Also, the reciprocating mass is much greater. When you multiple weight by 2 or 3 times and the air pressure that actuates things by 10, you get noticibly more recoil. Timmies aren't anymore blowbacks than Impulses, Angels, or Bushmasters. They all operate by having a chip send signals to a solenoid that pressurizes the chamber in front and in back of a ram or hammer or whatever at programmed intervals.