Sometimes the bore can be bored out and a liner installed but usually fitting a new barrel is easier.
Supply make, model, caliber and condition...it may make it easier to get a good answer.
Installing a liner in a pistol barrel is something that needs to be done properly. Except for 22rf, many smiths won't even attempt to do the job.
Recently, there was a thread about a fellow that had purchased a S&W 357 that had been sleeved to be able to reclassify it as a restricted rather than a prohib.
Whoever did the job, made it look good. From what I could see of the pics, everything should have bee OK. It wasn't. The lips on the forcing cone broke away. The barrel had been sleeved from the wrong end and was either epoxied or soldered into place. The liner shouldn't have been installed in that manner. The liner should have been turned down to the desired diameters from a barrel blank, then threaded and profiled to fit the receiver as one piece for the desired length. Then, the old barrel should have been bored out and epoxied or soldered to the sleeve with the remnants of the old bbl butting up against the newly profiled diameter at the muzzle. When assembled properly, this configuration works very well.
Now, if you have to pay someone to do this work, it is cost prohibitive and cheaper to buy a new barrel to have fitted.
In the case of the antique S&W, you need to be especially careful that the smith you choose knows what they are doing and of course are you willing to pay the costs for doing the job. My advice, sell it for what you can get and buy a pistol with a decent bore. Likely it will be cheaper in the long run.
As for that C96 Mauser, there is only one good way to fix the barrel on that pistol. The existing bbl needs to be cut off and the upper slide needs to be threaded to accept a new barrel sleeve that has been threaded to match the slide. There is an article about this on the internet I found by GOOGLING the process. Not many smiths are willing to go through the process and only a select few know how to do it properly. Again, it is doable but prohibitively expensive. Again, it would likely be cheaper to purchase a shooter with a decent bore. IMHO, it would be worth doing if the pistol could be picked up cheaply enough or to save a prohib from the furnace.
The smith is a 45 S&W revolver like a 45 colt, but the top break is a 44 Russian barrel. If the bore was enlarged by taking .010 or .011 off the sides I would have a perfectly functioning revolver
You may want to look into the thing's value before you do anything. A vintage Model 3 may be too valuable to much around with.
You would also need another cylinder to handle the larger cases or have the existing cylinder chambers reamed out.
I was trying to answer several questions at once. Sorry for the long reply.
If all your are planning on doing is opening up the bore to accept 45 cal and there is enough meat in the barrel to allow it and if the cylinder chambers will still be thick enough to handle the pressures of the new case after being reamed to accept it, go for it.
If you insist on having the bore rifled, that will weaken the barrel as well. Not by much but you will be getting close to minimum thickness already. Smooth bores and be very accurate so don't reject the idea without thinking it through.
what's the bore diameter right now you would want it to be aright around .446" or so and bore it out to that(getting rid of the lands) then it could be rifled to .452" or bore it to .452" and make it a smooth bore then you have something you can use solid bullets(should be good out to handgun ranges) and shot
It's not original. It is a mix match of parts, 44 Russian barrel on 45s &w cylinder
I would only need to take off 11 thousandths off all around the bore and then the barrel would work with the cylinder. Right now it uses necked down 45 cases and 44 bullets
So what you are telling me is that the chambers in your cylinder are 45 call all the way through???? OK, that would work but if you insist on rifling the bore, add at least .008 to .010 in to your figuring.
The rifling will have to be cut anywhere from .004 on up to be effective and that removes more metal.
You could try one of the Canadian barrel makers and ask them to drill out the bore and rifle it for you. That takes specialized equipment and not many smiths have it.
Some smiths you could approach would be Chirs Weber or Chris Wilcox in BC. Both are good and to my limited knowledge, both have the equipment needed to perform such work.