sorry yes I did try the mp5 midcaps and they are a solid unit so would say its a no go there. the mp5 hicaps might work with modification but dont think its to viable.
i did one of the m16 9 mm 100bb cap mags,
bit of a pain, but handy,
had to strip out the internals from a buggered mp40 for the pouter shell,
then mill down all the sides of the plastic 9mm m16 mag to slide in snug into the mp40 shell,
then open up the feed bay on the mag to fit the mp40 hop unit,,
all in all a handy mag, but a bit of a pain in the arse to make up, have a go but its quite alot of work even on a milling bed,,,, would hate to do it on a sanding bed or by hand 
i did think of offering them to costomers but its to much work for each mag,, so to much cash for one mag 
team shoot and scoot, TL
Ok, cheers. Looks like we're stuck with the lo-caps for now then. 
