I figured all those little corners on the threads would be easy to bugger up causing the lockup to loosen. But I'm not a gunsmith or machinist. David
If those corners got buggered up, it would more likely have the effect of tightening things up I believe. It's regular Joe's cramming the threads together haphazardly without keeping them scrupulously clean and lubed that wears them inordinately. That and taking them down repeatedly for no good reason.
One thing I have noticed with TD barrels is a lack of rifling wear at the muzzle from horny-handed enthusiastic cleaning rod usage. One distinct advantage of TD Savages is them lending themselves to cleaning from the breech. Could be just the samples I viewed though.
As with all things corporate since the beginning of time, I always go with economic reasons holding sway over engineering reasons when it comes to design changes in products. Whether interrupted or uninterrupted threads are "better" or not is a moot point. They undoubtedly saved $.65 by eliminating two broaching operations in the process of making a 99. That, spread out over 10's of thousands of units would've paid for the CEO's new Packard.