try some other mags first:
http://www.landwarriorairsoft.com/airsoft-magazines-c3/high-capacity-c51/dytac-300rds-bravo-magazine-for-m4-aeg-black-box-of-10-p3058
get a m8 to go halves with ya - but they are good cheap mags
cleaning gun/mags - not really coz the hop-up must be clean and dry
some may clean barrel with alcohol wipes, some may use a tiny - and a I mean a tiny bit of silicone oil
in barrel only but if any of this gets in hop-up you will need to strip and clean/wash in warm soapy water
or will need replacing - so in general to avoid f**king it up DON'T
(it "can" help in some cases but to save getting into a row/debate avoid any chemicals especially as it might be mag related)
some mags are just pure crap - yup got a few that are pi$$ poor at feeding
pop one of the above Dytac's in - lovely - suffice to say most mags that came with guns are still in their boxes
bought some jumbo 500rnd ones from Hong Kong and they last for ages.....
because f**k all comes out the bastid mags !!!! (pile of crap they are)
OK I could change spring inside mag and pi$$ ball about but Dytac do job great & just over a fiver each
suffice to say we got another box recently