Hmmm…warning…
i just tried using the lower fps, stock MCX rattler spring, in the sig …to try a lower fps spring.
It bloody jammed up and seized.!
I think the smaller spring colied over itself and grabbed…
Very hard to release the rear tap… it must have been locked back under compression…
got it out, after some swearing, and hammer work…
Stiff spring required.!
Even the New M95 spring, sees 320-330 fps…
I dont know if i’d trust a New M90, not to jam again…
It’s literally a piece of piss to cut and shut magazines provided they’re roughly the same size, and even if they’re not it can still be done.
Years ago I grafted a stick mag lower onto an M4 stanag upper for an M4 pistol build. Looked cool, worked fine, albeit shit capacity. M4 receiver, Vector suppressor for a handguard, Scorpion EVO / M4 mag. 
Rear wired to an XT30 plug, concertina battery wire ran up to a box attached to the sling.
With any custom mag, once the shell’s sorted the terminal wires and feed tube are easy. Same principle applies when you make custom drum mags… of which I’ve made plenty. 
Long barrel, really good JG seals, and they do have a tighter barrel than most… PME risk is damn high especially any spring less that stock one.
it seems to go okay on the M95…
I might be " stuck" with 330 fps…!!
I wanted to try it at 300…
Long barrel with good seals and m90 is probably around 330fps anyway.
The nozzle to cylinder head spout will loosen up a little and drop slightly over time but about 320 was as low as I seen out of them.
And xforce Monday morning just got busier
" I really really want…
290 fps, and accuracy out of it…
So…
Ported cylinder, and cut the barrel down"
" Why the hell did you buy a Long Boi.?.?!!"
Dont worry, i can live with 330 fps…!! 
It’s just a number on a chrono in the end…
What the squishy round thing does when it exits the barrel’s the important thing.
It’s not like you can walk around with a t shirt on that says “My blaster does 330FPS!”
… or can you? 
Yep…!!
