Do you know the old o-ring stretch trick?
 
	 
 
	Your airseal would have to be freaking horrendous to lose 200 FPS at the piston head/cylinder junction. For reference, I’ve done some work on certain Lancer Craptical guns that didn’t even have airseal between the head and cylinder, and still got over 300 FPS (supposed to shoot 375). I’m not kidding here.
 
	 
 
	When your nozzle is too long it can lose you FPS consistency, accuracy, feeding… usually not more than 10-12 FPS at max though.
 
	 
 
	My best bet is that you’re getting drag on your tappet plate/nozzle, if your tappet timing is off because of drag, it can easily cause that much FPS loss. Check for any friction between the GB shell and the tappet and the nozzle and the nozzle tube. Make sure you check with the GB screwed together tightly.
 
	 
 
	Oh, and also check and make your nozzle is at the right angle—if it’s angled it can do that.
 
	 
 
	Mag issues are a decent guess, methinks, but it’s been a while since I’ve seen mags do that—I’ve had feeding issues (darn you Lancer midcaps), and sometimes this causes FPS drop as well, but I’ve never seen 200.