[Flatlander]

Tephlon tape mod: Wrap tephlon tape (aka plumbers tape) around the hopup rubber and continue down slightly past the rubber onto the inner barrel (I go about 3/4" past). This prevents blow by: air blowing by between the hopup rubber and the inner barrel. Put a bit of oil or grease onto it to slide it into the hopup unit as it's usually a tight fit. I can only get one wrap otherwise the little C clip that holds the barrel will sit too high, causing the hopup/barrel to not bounce freely. I cannot stress enough how important this bouncing is with the hopup!

Me and a buddy were noticing low FPS on our m4's soon after upgrading. I did the tephlon tape to both of ours and it bumped up both about 40-50 fps. Now on some guns it has little to no effect as the rubbers are sitting tight enough on the inner barrels.