Up in the pinned topics, TJ's lists a .303-.311 10 twist liner?

My sneaking suspicion here is that moodyholler is onto something. I’ve read (which means I really have an uninformed opinion) that lining barrels needs to be limited to pistol calibers or low intensity cartridges. There seems to be a notion that cartridges at .30-30 levels or so, are probably not good candidates, much less .303 British.

Having written that, I had a Marlin 336 that had been lined to .25-35, and it handled factory loads with aplomb. I might have been guilty of pushing my reloads a little hotter, but I certainly wasn’t trying to make it into a .250-3000.

I’ve heard the Bob Hoyt will make a thicker liner, essentially a turned down barrel, so that might be an avenue to explore. Or turning down an existing barrel to create a liner.

Maybe a much better idea, if admittedly more expensive, is to rebarrel it.

Otony

Is the candidate rifle a Martini-Henry service rifle modified with a .22 rimfire liner for miniature rifle shooting societies in the UK? There were a helluva lot of them so altered. Also a heckuva lot of said alterations were done so by Parker-Hale (and so marked in tiny lettering on the muzzle), and/or done by other concerns using Parkerifled liners. I've seen and owned a few of them over the years and accuracy/function was not a given.

I too wouldn't be comfy with a 1/2" liner chambered for .303 British, and I wonder if there's any reputable smiths out there that would recommend it. I would ask John Taylor about it before going any further.

Were it mine I would either begin hunting for a .303 British take-off barrel, or bite the bullet and have a new barrel fitted/chambered for it if I really had an uncontrollable urge to shoot it.

Pic of breec

I would shoot/use it as is. Cool rifle.

Yes, that is the best approach.
I did that to an Army & Navy many years ago - done carefully the joint underneath was only visible with the barrel taken off.