Shaving a M4 mag

So it seems that Gen 9 drum barrels and trader mags are near impossible to come by. Any suggestions on how to shave the mag so it fits? I understand the idea but before I go ahead and potentially stuff up a nice working mag, I was hoping for some advice. TIA all

Not so much the mag but the mag well in the receiver. I have modified a lehui dual drum to fit an ACR. All it took was a little shaving off and it fits perfectly. Just take your time if you go down that path.

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Had success with gen 8 nylon drum mag, had to shave the back of drum to fit the angle of gen 9 receiver (circled part)