Range time today, electricians tape holding the magazine tube to the barrel until I shorten it to match the shortened, rechambered barrel.
Still having some feeding issues as a result of substituting a 3/8" shorter cartridge for the one for which the mechanism was designed. The magazine, metering stop, and lifter worked pretty well with up to ten cartridges in the magazine, but any more than that and any additional cartridges were too difficult to worm into the oversized tube.
Good news is the lockup is absolutely solid, the firing mechanism works well, and it shoots just fine.
The feeding jam is due to the lifter being kicked out from under the cartridge too soon by the bolt. That causes the back end of the cartridge to drop down and jam the nose up against the roof of the chamber. I'll investigate milling some metal off the bolt to change the timing of the lifter drop. Ideally I'd extend the little fin on the bottom of the bolt face and change the angle slightly to help "scoop" the back of the rimless .45 ACP case up a little higher, a little sooner, but that's not going to happen for several reasons all relating to the multiple functions of that fin (for one thing it bears against the bottom of the barrel and keeps the bolt nose from kicking up under bolt thrust loads) and my lack of metallurgical knowledge. I'll try to make it feed just by modifying the action of the lifter.
I'll also investigate buying a chrome-moly tube to make a smaller diameter magazine tube so the cartridges are easier to load through the gate.