Measure from the end of the muzzle to the front edge of the vent hole on the receiver on your Rem. This will give you barrel length. As to 22 in. vs. 24 in., ( and I'll probably hear about this one ), an OLD rule of thumb was you lose about 50 fps. for each inch of barrel length. This can be a very variable condition, but may be close enough to give you a rough idea.
I'm sure others on here will be glad to give you some further insight as to barrel length vs. velocity. Check some reloading manuals for data taken out of their test firearms and see what barrel length was used in load workup. We all know different manuals will give slightly different data, but it is a place to start, and give you some ideas.