Too tight piston seal?

[spevie]

What happens if the piston seal is too tight? Is the gun underpowered, or if REALLY too tight, will not fire at all?

[Mark 611]

It'll shoot but you will have lost alot of power velocity wise!

[Motorhead]

Correct 

[spevie]

Thanks to you both. The AG, an early Walther LG55 was a worn club gun. The replacement piston seal (JG, only source I know of) was 0.4mm oversized, everything else about the gun somewhat worn...with the correct seal, it's quite accurate, smooth: nice antique match rifle!

[nced]

What happens if the piston seal is too tight? Is the gun underpowered, or if REALLY too tight, will not fire at all?

"Is the gun underpowered"
Yep

"if REALLY too tight, will not fire at all?"
Possible but not probable.

IMHO, there is more of a possibility that the gun might be damaged if the piston seal is TOO LOOSE!

[Roadworthy]

Yes, the seal being too tight can (probably will) cost you some velocity.  It can also set up a vibration as it travels through the compression tube.  You are unlikely to feel it due to everything else going on but it can manifest itself in slight variations in your groups.