Unknown Mags for MP5 don't work on my MP5J TM
 

I bought these high cap MP5 clips for my Tokyo Marui MP5J. I place the BB's inside the mag and inserted the clip to my rifle. I wind the gear under my Mag. I shoot a few round then it jams. Everytime I pull the trigger, the noise sounds muffled. When I take out the clip, BB's that were in between the Mag and tube, where BB's are feed through, drop out (not uncommon). When I pull the trigger, the gun seems to work fine. The high Cap mag that came with my TM works fine. Same concept. To me it sounds like a feeding problem or the mag just won't fit in my gun. Does anybody else have an idea? Any help is much appreciated.

Try dropping a couple of silicon oil in your empty mag then load it to spread the oil and finally fire the gun to test.
I had a similar problem with some King Arms mags and was able to "fix" them by doing just that.

There is more info about this here

Thanks Dao. I will try that first and let you know.

Silicone oil is what I'd suggest too, although it seems to have less of an effect on highcap mags than on spring-fed mags

Had the same problem with mine. Couple drops of oil fixed it for me too.

Same here. Had 8 mags only one fed correctly. Lubed them all with silicon, loaded and now they work great. Your gun may shoot a litle eratic as there will be a fair amount of silicon lube on your BB's for a while. Makes your hopup do some wierd stuff, till it settles down.