What might be my issue? (AEG M4)

[Mr. G36!]

So I had a JG M4 and it worked very well. I've never opened the mech-box, so that should be good to go. I switched out the body for a Guarder metal one, and the barrel (inner & outer) for G&P ones. As such, I also replaced the Hop-Up twice, once with a G&G, and now with a Guarder.

Basically, there's some horrendous feeding issue. The FPS is consistent when it actually fires, and the Hop-Up seems to work as well, but the gun only actually fired now and then, leaving most of the BBs stuck inside the chamber.

It's not the mags, because I can't seem to find any by any company that work consistently. And I've tried different Hop-Ups, and have the same issue regardless. The barrel is fit properly, so the rubber isn't twisted or jammed, and like I said, when BBs do leave the barrel, the FPS and trajectories are consistent.

So what might the issue be? I can't shake the feeling that it's just a Hop-Up incompatibility, but since I've tried a few, I'm thinking maybe it's the fitting of the body? Or maybe the JG mechbox just won't work properly with other brands? I dunno...my work with TM items has never failed me, but this JG thing is really annoying me. I was thinking of just getting a whole new mechbox, but I don't know for sure that that's the issue, so I'm looking for some advice first.

Thanks!

[Styrak]

Tried pushing up on the mags when firing? Or twisting them forward or backward and then firing?

[Mr. G36!]

Yeah, makes no difference.

Is it possible that the receivers are just a poor fit with the mechbox? I could understand that throwing the rest of the components off...

[Styrak]

Has nothing to do with the mechbox (well actually it could be pressing on the hopup), and has everything to do with the receiver/magwell and hopup chamber interaction.
Your mags aren't high enough in the magwell it would seem (but you tried pressing up and it didn't feed either, which usually fixes that)

Not sure what your problem is. I'd have to work with it in person.

[Mr. G36!]

I think the receiver is slightly...not misshapen, but it's not allowing the mag to properly contact the chamber. Maybe, like, the hop-up is sitting too high, or the mag-catch is too low or something. I'll try some different things...maybe remove the mag-release altogether and see if the mag just isn't locking into place high enough. I guess it could be a number of small things, eh?