Thanks for that suggestion, Richard. It does sound like that is more of a permanent adapter arrangement than I had in mind but I DO appreciate that input.
I do have the rubber adapter for the Mossberg 500 and we tried it out at the range yesterday. We fit 8 in the tube, cycled one into the chamber, and re-added the 8th for a total of 9.
We regular cycled, slow cycled, fast cycled, cycle at odd gun angles and the mini-s fed every time and extracted fully every time.
Recoil, as expected, was minimal. Accuracy at 50 yards was good (t/- 5 inches) considering we were free standing and had to make a few tweaks along the way.
Power at the point of impact was very good and, IMO, fell into the "Get 'er Done" category. Full pass through the 3/4" yellow pine backing with a big cloud of dust from the berm behind.
We had the Mossberg 535 that I had bought out of a pawnshop in Texas. Tested it out with some birdshot, switched to some rifled slugs, and all seemed fine.
Switched to the rifled barrel and 2 3/4" sabots and ran 3 boxes through. Again, all seemed fine.
My buddy had given me a shotgun shell belt holder full of Winchester Super X 2 3/4" slugs, so I figured I'd give them a whirl. I'm not sure how old these OLD shells were, but by the appearance of the brass casings, they weren't spring chickens, so if we were going to full test the 535, let's see what it would do with probably-not-top-notch shells.
Fired 3 tubes worth of the Super X's, and I called it quits. The 535 ate 'em up, no problem, but it was like I was firing a black powder muzzle loader. Smoke city !
I told my son that we'd keep the rest of the Super X's for last ditch effort level. Inspecting the receiver/breech was interesting: dirty as heck.
To give the 535 one last test, I swapped back to the rifled barrel, dug into the ammo box, and pulled out two Brenneke 3" Magnum Crush shells. 666 grains.
I told my son I'd fire the first shell, see how it went, then if he wanted to, he could fire the second shell.
I fired the 1st Brenneke using the lead sled, and was glad I did. A LOT of recoil, as expected, but the 535 checked out okay.
My son had developed a nice rhythm to firing the 2 3/4" shells: good stance, hug firm (but not to the point of choking) and rock straight back SLIGHTLY with the recoil. I warned of the much greater recoil, but he wanted to try it freestanding. He did, and managed to hit the 50 yard target level and about 4" right.
He said with a grin, "Well, that was a mistake". : ' ) He had used great form, though, and they don't call it "Magnum Crush" for nothing. The berm dust is probably still settling. : ' )