The Baikal combination gun

[Ian]

Interrupted threads and a knurled jam nut?

I have two Savage 219s (one from Utica and one from Chickopee Falls), both .30-30, one has its original 16-ga. barrel/forearm and the other was sold before I bought the rifle/receiver). The comment about them always being set the wrong way is the way it is in the field for sure, but you CAN carry the spare and ammo in a pack and switch out in the field.

 

[fiver]

just build them like an over under shotgun, and swap the barrels out.
if they hold tolerances it's wouldn't be a problem, and regulating the barrels could easily be accomplished with a hanger system.

 

[Pistolero]

Seems perfectly doable for anyone with a mill and lathe and the will to make
another barrel set. Machine up a block of 4140 for the breech block and thread
a shotgun barrel and rifle barrel in and chamber. Extractors would probably be
best purchased and the grooves machined rather than making from stock.

If you didn't want to do the threading, medium press fit, heat block and press barrel,
and a pair of pins would do it, too.

Then an adjustable forward barrel block to permit regulating the barrel POIs.

Forearm hanger and done. Not trivial, but no magic anywhere, either.

Bill