Low fps with 1.4J spring
 

Ok gents, I've got a 1.4J KM (120M) spring in my V2 GB and it's only shooting 330. The rest fo the GB internals are as follows; TM piston and piston head, gears, tappet plate; SRC nozzle, cylinder, and cylinder head.

It has been suggested to me that there is an air leak. Schwag suggested I check my hopup sleeve and see if it was in a oval shape instead of round. I did and it is round. Now I personally think that some of the problem has to do with the SRC parts but I don't know enough to make a fully informed decision.

What gun is it and what inner barrel (bore & length) do you have?

It's an M16A4, It believe it's a standard size M16 inner barral, sothing like 509mm.

Could be your nozzle isn't mating properly with the hop up unit you have. I've experienced that by changing a square nosed G&P nozzle in an SPR with a rounded one, about 60fps airloss was common. I swapped the hop up unit out for a different one, gained about 40-50fps in increased velocity.

Might also want to check your piston head's o-ring seal.