[Dynamo]

did you have this issue with the orriginal nozzle?
also is your gearbox orriginal or upgraded?

i have been having feeding and powerloss issues with my M4 for a while.
i finally found out the problem after trying different hopups, barrels and pistons. it turns out that the new gearbox i got sits farther back than the orriginal one, that and my new nozzle was also a bit long by 0.3mm.
so my orriginal nozzle was too short and my new one was too long.
lucky for me that the new nozzle is metal and i was able to turn it down in length, so now it fits perfectly.

this caused really bad misfeeding, the BBs would drag the hopup sleeve lip into the barrel and jam. 4 pistons later i got it all fixed.

try sealing the end of your barrel and dryfire in single shot, see if you get back pressure in the cylender or if you piston still slams forward.

getting everything to line up is a real pain, especially when mix/matching parts.

it's also a bad idea to bolt your stock bolt through the back of your gearbox.
like the others have said, see how big the gap is between the back of the gearbox and the inside face of the lower reciver extension, and make your self a shim so the bolt wont pull the gearbox back.