Both of my old Hornady manuals show starting loads well above 4.7 gr of Bullseye, 5.8 gr (4th Edition) or 5.9 gr (7th Edition) for a 200 gr swaged SWC in 45 Colt. Both these loads claim 850 fps from a 7-1/2 in bbl Ruger Bisley Blackhawk. Your 4.7 gr load must be well down from 850 fps, but that should be O.K. with fast burning Bullseye. The exception might be a deformed, damaged, or internally defective swaged bullet. I quit using swaged lead decades ago. No matter how slow you drive them, they will eventually lead. If you mess up and push near 1,000 fps they shrink the bore of the handgun with lead right away. Why does Hornady show loads that push them this fast?? That big scallop on the side of the bullet came from either a defect in the lead wire, a cold joint or slag inclusion, or perhaps a gouged out on bullet seating, maybe from a case mouth not flared enough that carved the bullet O.D. on the way in. Evidence is gone for that mishap now that the case is "fired". Bullseye lights off right now unless the confinement of a defective bullet and/or seating makes it act like a Roman candle, which might account for the funny report you heard. Hot gas got into that small channel and made a big one out of it, obturating the O.D. of the bullet to the I.D. of the case and sticking it before the bullet could move. There was not much gas pressure pushing on the base. If powder got into that fissure before firing, then stage was set. Hot gas flame-cut down the side of the bullet and shaped that lovely spire on the bullet nose. When I was a stupid kid I did near the same thing with a soft air rifle pellet in a .22 long rifle case. I hate soft lead bullets. Will not use them. Soft lead is O.K. for patched round balls for muzzle loaders and not much else.

Edit: My bad. I was looking at .45 Colt loads, not .45 ACP. Lesson learned, never believe loading data on the Internet, especially mine. 4.7 gr of BE running a 200 gr. lead punkin ball to 900 fps is on the warm side for me. Swaged lead is better suited for caulking up joints in bell & spigot cast iron pipe. Just my prejudice.