JG M4 S System

I have a DPMS M4 s-system and a JG M4 s-system aeg. I bought the both used from ebay. One is well used and the other is a good bit newer. I have noticed when fireing that both weapons will not empty the mag completely of the bb's that i have wound into the feed slot of the mag. And this happens randomly, I mean I may fire 10 rounds then it mis-feeds and after winding the mag it may fire 20 or 30 rounds. I wind until i feel good tension on the spring. Am i not winding enough or could the mags be worn out or is it a feeding problem with the weapons? Any info on this weapon would be helpful.

sounds like the magazine needs to be lubed?

most high caps i've seen give a click when wound all the way

Ive had a jg m4 s-system was a good gun no problems right out of the box.Sounds like a mag problem honestly.mags can get dirty and or might need cleaning.Make sure the channel is free of dirt or gunk and the bbs u use are high quality

thanks guys, i didn't get a manual with either weapon so it turns out i was not winding enough. was able to empty a 340 capasity mag with one winding today. looks like problem solved.

good 2 go mission capable