One of my favorite firearms is a Remington 7615. It is a pump action rifle like the Remington 760, but is chambered in .223/5.56 and it takes standard magazines. I can attest to the fact that 10 round Bushmaster and PMAG magazines operate well. The gun is well-made and sturdy. Only problem is that the original recoil pad, from a well-known manufacturer, gets gooey and needs to be replaced. I think the original thought behind it was to provide a high capacity -- but not semi-auto -- patrol rifle. Another selling point was that it operated like the widely used Remington 870 shotgun.
Curiously, as of today, July 15, 2019, there is not a single Remington 7615 for sale on GunBroker.
Here is an Internet picture from a 2006 online auction: