Acer-m14
20×102mm Vulcan
i know this is late .. but if you need to block the 10 rnd pined mag to 5 ,,.. the Mosin 7.62x54r case works for the Grendel round .. and the rim sits just cozy on the spring .. no trimming needed ..
I have a few of those. Good for 4 rounds, won't accept the 5th. Might trim mine just a bit for the last round.Just buy a Magpul 10 round magazine and a Magpul 5 round limiter. Put the limiter in when you are hunting and take it out when you are at the range or whatever. Minus 5 Round Limiter – PMAG® AR/M4 GEN M3™, 3 Pack (magpul.com)
I had the same problem and I trimmed the limiter a little.I have a few of those. Good for 4 rounds, won't accept the 5th. Might trim mine just a bit for the last round.