by Jim in Houston » Sun Apr 08, 2018 5:47 pm
I have used a variety of 20 round magazines, both steel and polymer. Brownells is one brand of steel; Magpul's P-mags for polymer.
You should be able to get up to 7 rounds loaded. If you will be hunting, some states limit the size of the magazine. In that case a 10 round mag may be what you want to hold four or five rounds.
The straight sided magazines work the best, as the 450BM cartridges don't go around the curve in 30 round mags very well.
I have used both with the 5.56 follower and with a 450BM (black or blue) follower.
Life Member, Texas State Rifle Association; Patron LIfe Member, NRA