I didn't retire, just...
still waiting on the gunsmith to get around to my problem.
Since he still has my gun, I can't try any of the suggestions you have all given - but I appreciate all of the input.
One question was about how successful loading the first round went. The answer is that it was 100% reliable, coming out of the magazine and going into the chamber.
Also, the first round always ejected perfectly.
I'm wondering if the 2 & 3/4 inch shell cycling into a 3 inch chamber has anything to do with it?
Meanwhile, my 12 ga 870 WM, with 2&3/4 inch chamber cyles perfectly. I am shooting rifled slug loads in it, trying to find a brand it likes. So far, I have tried Fed Truball (Foster) slugs, and a Winchester PD (Foster) slug.
I get about a 3 inch group @ 50 yards with both of them, but I will try some Rem (Foster) slugs, also. The Win PD slugs shoot about 9 inches higher than the Fed Truballs @ 50 yards.
The barrel is a 1970's vintage smooth bore, 20 Inch (IIRC) with a Bushnel Magnum Phantom pistol scope mounted on it.
Artillery lends dignity to what would otherwise be but a vulgar brawl.