UPDATE!
My son's SBE came in yesterday, and I tried it this morning. I want to note that it is a "used" gun, but I am not sure how much. I tried some 3 3/4 dram high brass shells that cycled fine, but the 3 1/4 dram 7/8 oz "target loads" would not cycle at all. That was all the ammo that I had handy, but I intend to try a wider range of ammo to see exactly where the gun quits functioning.