To my mind, the model 6 is a true rolling block. The lock up is exactly the same. Remington made the receiver longer to give the barrel a 2 inch steel cradle to sit in making the take down joint much stronger. That made room for more space between the pivot points. The block still rolls down, but at a wider radius. They replaced the spur at the top of the block with a side mounted spur. The Improved version has a smaller extractor that comes through a slot in the breech face and the new half cock only loading feature. The one I saw had a 24" barrel and a longer fore end stock. Don't know if there were barrel length options or if they all came with longer barrels. Hard to research this stuff. Right now, An improved model 6 is my grail 22 plinker, but I did find a rossi Winchester 62 clone with problems on the cheap that I'm considering.