Yep, if it's not threaded for choke tubes, then it's generally called a "fixed choke". Fixed choke remington barrels usually have the type of choke stamped towards the rear of the barrel. The four main types of choke, in order of increasing constriction, are cylinder (no choke, AFAIK. also called open. Stamp will read "CYL") Improved Cylinder, (stamped "IMP CYL") Modified (stamped "MOD",) and Full (never seen one, so I'm not sure about the stamp.) Less commonly encountered are things like improved modified, and extra full or turkey chokes.
There's no problem shooting standard shells in a magnum receiver. In general, you can use shorter shells than what's stamped on the barrel, but not longer. You have to pay a bit of attention here, because the shell length refers to the fired length of the shell. Thus, you can chamber a 3" shell in a 2 3/4" inch gun, but you can't expect to fire it safely. (not sure what would happen, exactly, and I'm not eager to find out first hand-like.)