Aim surplus have dedicated 300. B/0 mags
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Pmag has come out with a dedicated 30 round blackout mag, with a wider front edge. I haven’t tried it yet. Git one and give us a review.
https://gunmagwarehouse.com/magpul-pmag-gen-m3-ar-15-300-aac-blackout-30-round-magazine.html
https://www.aimsurplus.com/product.aspx?item=MMAG800BLK&name=Magpul+PMAG®+30+AR+300+B+GEN+M3™.300+AAC+BLACKOUT+-+Black&search=Blackout
^^^^^^^
I hope the mags work for you, however, the bullet profile is what's getting you hung up, not the mags. I had the same problem with round-nose 110gr supers. The feed-ramp profile is cut the same as 5.56 and requires a pointed projectile.
If you want to stick with the flat nose...you may need to get the file.