Post by Mark
Actually,
The 20 round steel magazines really don't need much more than deburring the undersides of the feed lips as they ended up with many burrs and extremely sharp edges when they where stamped out. That, and the aluminum followers usually need some burrs removed as well (be careful though, these followers bend easily)
I recommend for you to disassemble your 20 round (standard) magazine and take sand paper or emery cloth and sand the undersides of the magazine lips smooth mostly to eliminate any really sharp or burred edges.
The aluminum followers also have another problem: The last shot hold open activation doesn't always work as the Marushin follower "Submarines" (the front of the follower isn't properly supported) and so the front end of the follower dips down while feeding the last cartridges and the activation pad misses the last shot hold open lever.
This might also be the jaming problem..There is only one fix that I have seen: Glue a small piece of ABS or some other plastic etc to the back of the follower ( The small "pad" ) and that might help.
Otherwise, to really fix the "problem" a new follower is really needed. Unfortunately, the Marushin 20 round magazine uses a really short follower that is due to the cartridge length block. The follower in this case doesn't interchange with the real cartridge follower that the AR15/M16 uses as they are much longer.
The 30 round magazines are much better made and they are further made from aluminum alloy and these rare magazines, resemble the real AR15/M16 magazines to the point that many times, I have had to look twice to confirm that I was taking the right magazines for my real AR15 to the range. These magazines have full length followers and no cartridge length block like the 20 round magazines have.
The only mod that I prefer on the Marushin 30 round magazine is to change the follower to the late model green plastic M16 as it helps the feeding as well as the last shot hold open functions better as the front end of the follower is supported better.
_________________
Wanted to buy: MGC Sten MK3....trades?(still)
MGC MP40 Marushin MP40 Nakata MP40 TRC MP40
Modelgun manufacturers, past and present:CMC,CAW,Hudson,HWS,LS,MGC(R.I.P. 1960's~2007) Marushin,Marui,Kokusai,Shoei,Tanaka and Western Arms