[ZX12R]

I did have a rifling machine I made out of the differential from a riding mower, and I reamed and rifled a few old shot out barrels. It is a lot of work!

Yes, rifle barrels would be the toughest part, along with the rifling. And accuracy would be hard to maintain without modern equipment, but to a determined and reasonably intelligent man, anything can be accomplished. Much easier to just buy one, though.

It's the same way with telescopes. I've designed and built a few of my own. You can make your own mirrors too, but the investment in time isn't worth it. You can just buy them pretty cheap and make the rest.

[SWAMPSNIPER]

I locked one drive axle, mounted the differential on a slide. There was a length of motorcycle chain in a groove that ran the length of the bed for the slide, had a sprocket on the other drive axle. The cutter head fit on the input shaft and would rotate as the differential was pulled along the slide with the sprocket engaging the chain. I could adjust it with different sprockets for any pitch I wanted.

Round ball barrels use a slow twist, 1 in 48 is considered fast, nothing like the modern barrels.