a long time back some folks were asking about the excellent P-mag for use with the 5.45x39 round.
i did try to use the 5.45x39 in the early P-mag and found they couldn't feed more than a few rounds reliably.
last year a bought a new batch of P-mags and seeing a few people on youtube claiming that the new windowed mag will feed 5.45x39 rounds stock i thought i got to try this.
out of the latest batch of P-mags the standard non windowed types 8 out of 10 will hold and feed 26-29 rounds of 5.45
the two that won't feed the rounds are OLD STOCK and still have that little ammo divider thing at the front of the mag opening.
the P-mags without this are the new versions and will feed a good number of 5.45 soviet rounds without modifications.
several of these mags have run 29 rounds of 5.45 with no hiccups so far.
they run like their made for the 5.45 at about 20-25 rounds--
so the newer makes of the p-mag do work with 5.45 with a smaller amount of ammo. as all ways YMMV!