Isn't there a Remington pump rifle that uses AR magazines?
Remington 7615P (Police). Based on a Remington 870 20 gauge shotgun chambered in .223/5.56. Takes AR mags. Mine has ghost ring sight, I believe the rear sight is Wilson Combat and the front XS (possibly). Surprisingly accurate. No longer made. Originally retailed north of $700. I have noticed prices going up on these as might be expected. Mine was a police trade-in and $325 pre-hysteria.