A Remington 7615 magwell might work; it had a built-in feed ramp. A Galil AR adapter might work. MGI make a modular lower. I think the mag sits too high to use a standard AR magwell, the receiver interferes with the release; the 7615 magwell has a lowered mag release button. MSA (texasakdesigns.com) has an adapter and is promising to debut an all-in-one magwell/trigger guard assembly.