Originally Posted by Warlock
Fitting issues could be related to the AEG Brand/model magwel.
Feeding issues could be related to poor hop-up alignment. A cheap hop-up unit like the stock one in most gun could cause misfeed, so replacing the hop-up for a better unit could solve this problem.
Green label PMAG fit and feed flawlessly in all Classic army m4 I saw
I think it's a lot simpler than that and not necessarily related to cheapness or quality. I'd say it's about specs and tolerances.
It's clear from just reading around and listening to players and looking at the most common fix -- holding the mag in manually or using tape -- it's clear that the Marui design for the hopup + mag mating sucks and is long overdue for a major reboot .. It's not without precedent. There have been other fixes to Marui designs (Ajax STS, etc). The tolerances for the mag-to-magwell/hopup feeding shouldn't be in the sub-millimeter range. It shouldn't be up to a tiny little mag release latch to be the only thing holding the mag up high enough so that the hopup tube can push the spring-loaded port open. Look how nicely the pistol grip's motor height adjustment springs solves a similar problem of bringing together two items made by separate manufacturers. I would suspect this problem can also be solved in a similar manner.
The current bug in the design is that the length of the feeder tube has to not only account for accepting BBs and not going too far into the mag, but also for forcing open the door which holds the BBs back. If the action of mating with the mag's BB exit and door/latch open were to be decoupled or moved apart, we could allow for wider tolerances in differences between manufacturers or even batches of production runs.
When I compare a G&G hi-cap mag (works unmodified in a G&G M4) to my green-box PMAG (requires mod), the difference in height of the mag's port is fairly obvious (from memory, approaching 1mm). As far as I know there aren't ISO specifications for these things, people are just making products to some close-enough range of dimensions and hoping for the best.
... Or maybe the walls of magwels should be lined with springs that are activated by the insertion of a mag.