How many here collect deacts or obsolete caliber pistols?

[Korium]

Even if you could forget the legal issues involved about overall length: wouldn't the 12 inch barrels make the LBR's too muzzle-heavy, without the counterweight and bracing ability of the brace?

Quite a few people have the brace removed, replacing it with a straight metal rod and counterweight.

there are some turn of the 20th century auto pistol caliber pieces that should qualify: stuff like the 9mm Steyr, the .30 Mauser, the .35 Remington. . .

.30 Mauser should still be factory produced.

Not sure any do. I saw an excellent C-93 for sale a while back, still S5, despite being chambered in 7.65x25mm Borchardt (bet that's an awkward proposition to source).

Something like the Mars might qualify, seeing as they were made in various weird, proprietary calibres.