The model 31 was designed on the model 17. Remington was competing with the model 12 at the time and many shooters preferred the side loading feature of the model 12. The model 17 was redesigned to make it side loading and was renamed the model 31.
I have two model 17s, one with a 28" plain barrel with a weaver choke and one with a 30" solid rib barrel. I have a Grade B with a 28" solid rib barrel on the way.
I have only been shooting these guns for a couple of months, but long enough to know I love them.

Pete