For most shooters a round count is a best guess situation, even with written records a field gun is still a best guess 90% of the time. In this case all I do know is the rifle still shot well when put up. The owner stopped shooting rockchucks and ground squirrels, many years ago and the rifle has set dormant since that time. The loaded rounds are loaded with H-870/AA-8700 which has not been "made" by Hogdon or AA since 2002. And the owner was not aware that H-870 was no longer made. Yeh, sometimes you must be a shade on the detective side. But with 50+ years in gun buying, it is not my first rodeo.
I have started my normal bore cleaning sequence on used guns. Tonight I will fill the bore with Shooters Choice (copper solvent version) and do a week's soak. Any copper will come out in gobs and we will be back to bare steel and as new a barrel surface as there is in this bore.
By the way, I sat down last night and determined the shoulder's base on the 280 was moved forward the length of the factory shoulder. The capacity of the case is 72 grains of water. The cartridge has 1 grain more capacity than the 240 Super Varminter listed in the Ackley Vol 1. So we shall see, as always, "the proof is in the pudding."
Best,
Ed