there is a post/statment that I made with reguards to a 5,56 boldt head and carier fit to 5.56 mags.
" like this ( photo), (photo). funney this you bring this up my rommy "G" B/C pass right thrue a 5.56 mag. when my camra recharges its batterys Ill post a photo of what my -47 B/C looks like with a SAR3 mag. muttman "
Biggun you were correct with reguards to the k-var 5.56 mags if they are made like the -74 mags.
first thing to eyeball is the mag feed lips span on a 5.56 mag.
promag - 11mm
-74 mag - 11mm at breach side and < 11mm (10.9mm) at the buttstock side.
next thing is the part of the boldt that pushes the case out of the mag, keep in mind that this part on a -74 boldt is 9mm wide.
bulgy 5.56 boldt head - 11mm. and the rommy B/C at the part that fits in the mag is 11mm
here are some photos of boldt head to mag and B/C to mag fit. the 3 mags were promag, sar3, bulgy-74. muttman