Browning A5 Magnum won’t cycle

As the title says I have an A5 magnum l. It sat for probably 20 years before we pulled it out of the safe and I shot it. We cleaned it since it wouldn’t cycle but it still won’t, it attempts to though as the bolt does come back a bit but not enough for the spent shell to come out. The only thing I could think is that it doesn’t like regular shells instead of the magnums but I wanted to be sure before I went out and bought some magnums. Could it be anything else?