StrangeRanger

Don't know about Frank's book. My copy went with my Reising when I sold it Small Arms Review says Numrich acquired H&R's inventory in 1986 https://smallarmsreview.com/the-u-s-45-model-50-and-55-reising-submachine-gun-and-model-60-semiautomatic-rifle/ FWIW Wikipedia agrees but I would never accept Wiki's word for it without independent confirmation https://en.wikipedia.org/wiki/M50_Reising (last paragraph)

The S- prefix on the S/N indicated it was assembled by Numrich in 198(7?) out of parts that they acquired from H&Rs closing. I can't see the sights or the barrel but the trigger guard, mag release, taskedown screw and selector lever all appear to be correct for a Numrich gun. Those two 20 round mags are worth their weight in gold

All springs eventually take a set when they are compressed and/or when they are cycled. This even includes the normal compression with the bolt forward. Replacements are readily available from Wolff Realistically on a display gun what does it matter?

Steel parts can fail under very low loads after an extremely high number of load cycles, meaning the impact of the gun on the tab during recoil. How many cycles did a Thompson see in 80 years including at least one war possibly three?

Not true. My Savage M1 (not M1A1) had an original 1 piece grip mount. The tiny lug that abut the barrel just in front of the threads and holds the mount into the receiver sheared off. The result was a "pump action" TSMG. Replaced it with a repro from Waffenmeisters which I expect to last another 75 years. It has been alleged elsewhere on this site that the grip mount has the highest failure rate of any TSMG part

There's a reason that it's called artificial intelligence

When they designed the gun, they probably didn't realize that the grip mount was going to be one of the highest rate of failure parts on the gun. They expected it to live forever

Simple case of the seller causing confusion by providing too much information

How is it head-scratching? The NFA/Transfer information is completely straightforward and by the book. The price may be somewhat "aspirational" depends on how badly you want a .308 belt fed. And $29,999.99 is SO much less than $30K 🤣

No new rule at all. it is the same as any other transferable SMG manufactured prior to the May 1986 ban on the transfer of newly manufactured FA weapons to non SOTs.

Thread pitch gauges, both metric and imperial, are cheap and readily available at either Lowe's or the Home Despot

Try bedding the tang in Acraglass

Tube guns are typically $20K asking price, matching/non-matching is more or less meaningless on a tube. Your $20K ask is a good deal for both parties since it is an Andrewski rebuild and includes $700+ of extra mags. The dealer who offered you $17K probably wanted to skim 5 of the mags and flip the gun at $20K. Hang in there it will move at $20K

The side of the receiver looks like it's flat and there's a vertical foregrip. That's why I guessed the M6

Ingram M6?