Now see this is brilliant. This is a semi or automatic rifle so your dominant trigger hand has to be the closest to the body for ease of movement: but because the body's hugging the gun you canhave this half wheel innovation. It dovetails beautifully with the gun's construction because it braces the banana clip from getting knocked around. Also when the magazine is spent you can pitch it and use the semi circle as a pummel guard for your hand. After that you can just start hammering away at people.
I would say though the inside of the magazine slot needs to be angled so the clip can just roll straight in, guided by the hand guard. As is though I think a marine could simple shove the magazine upward and toward their body and it would slide in with ease.