I believe it replaced the model 600 remington, which had a vent rib barrel. If i'm correct, they were chambered for several short action calibers. The Magnum version was chambered for 6.5 mm remington magnum and 350 remington magnum. The 350 is the most collectable. The 600 and 660 had a strange "dog leg" bolt design that caused a bit of knuckle bruising especially with the 350. I like the guns myself, but the 6.5 and 350 never really caught on. The magnums were short and lite, and the 350 killed at both ends if you know what I mean. Check me out on this info, cause it's been a while since I have dealt with them.