TM M14 airseal issue?
 

TM M14
-metal bushins
-good shimming job
-M120 spring
-metal bearing spring guide
fps: 398

(want to bring it to 450fps)

-Prom airseal nozzle
-PDI 560mm 6.01mm tightbore
fps: 320

(did I not grease it enough?)

-Madbull M130 spring
-lots of grease added
-280fps

(Maybe there's barrel suck because of the 560mm inner?)

-replaced piston o-ring with a new one off a stock TM piston
-installed a slightly larger o-ring inside the airseal nozzle
-swapped stock barrel back in
fps: 109

Unless mentioned above, the parts are stock. Battery is an 8.4V 4200mAh made from intellect cells. Chrony with BB Bastard 0.20mm BB's, chrony is the Madbull shoot through blue one. Chrony and BB's tested with my TM springer, records 210-2200fps, exactly what it should.

Anyone run into something like this before? I have tried removing grease, over greasing, and everything else I can think of and these are the results. At this point I'm ordering a Guarder full cylinder set to replace the entire compression assembly (piston head, cylinder, cylinder head, and nozzle.)

Did you ventilate your piston head?

stupid question but did you clean your barrel as well? a 6.01 is awfully tight and since you might of over greased it there might be gunk in the barrel

Its a stock TM piston and I haven't modified it at all. And yeah, the barrel was the first thing I cleaned, had issues with a very dirty 6.03mm a little while ago.

I think I may have found the problem though. Looks like a crack in the cylinder head and the brass tube the nozzle goes on is buckling so the air leaks right out of it.

That'd do it. I recommend getting a Prometheus cylinder head to match your Prometheus nozzle. It's always good to match brand.