Multiple locking lugs from splined couplings ?

[Waterworks]

I noticed that these standard splined couplings are a few easy machining steps away from an AR style multiple lug bolt and barrel extension, the question is how strong can this grade of alloy called 45 S 20 be heat treated to ?

 

[wyop]

https://steelss.com/Carbon-steel/45s20.html

 

[Dave W]

Some of the old Newton rifles used an interrupted buttress thread. I've looked at pictures of those, and noted that McMaster has 4130 Acme thread and matching nuts, if you didn't want to cut your own.

Make the nut into an Armalite-style barrel extension, and cut the rod into a Savage-style floating bolt head.

 

[wesg]

Too many lugs ... not enough rotation for extraction.

The AR gets past that by using the bolt carrier as a slide hammer.