I purchased a Model 41 a couple weeks ago (made in 1982). Since I had never shot this pistol before I decided to give it a good cleaning before taking it to the range. As soon as I removed the barrel, the slide stop was unable to hold the slide and the slide moved to the forward position (if I hold the slide stop lever in the up position the slide will not do this.) Is this normal?

The slide stop is Spring Loaded to hold it away from the locked position.
If there is No magazine installed in the gun, The slide stop will not engage when you pull the slide rearward.
Once you remove the barrel, your next step is to continue pulling the slide to the rear, Removing it from the frame.