Is it a good idea to swap a used barrel onto a K frame?

It isn't necessarily a BAD idea. There are issues, like barrel profile and match-up to the frame. I've done it. I've had it done. It works if done properly. It depends I guess on what the object of the exercise is.

Which model K-frame and what is the desired goal of the swap?

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VCDL, GOA, NRA

If the used barrel is in good shape (clean and strong rifling, forcing cone ok, threads ok, and crown not damaged) I don't see a problem, as long as someone who knows what they are doing installs it.

A 65-? into an original 3” S&W takeoff barrel.

Still looking for a host gun, but a few times a year I hear of one that Bubba hacksawed and made into a 3” so I am hoping a reasonably priced donor gun is nearby.

Interestingly, I found a LNIB LadySmith that was priced too low. Unfortunately, for the first time in decades I was not able to make the 175 mile round trip. The LadySmith sat for what seemed like forever, and I still managed to miss it.

Visually the barrel should be good to go. If I had a smith to do the work, I would check for sure.

Part of the reason I asked is because way back when S&W quit pinning their barrels, I vaguely remember a discussion about both Smith and Colt relying on torquing and “crushing” the threads to keep the barrels in place. Don’t recall if that was marketing hype to explain removing the pin or something else.

Here are my 64-6"s. I had an early "pencil" barrel installed on one of them. One of my favorite revolvers.

Attached Images

64s.jpg (74.7 KB, 39 views)

I got this circa 1948 M&P really cheep because the barrel
S/N is mismatched and its old stocks were awful.
I'm very happy with it even though nothing matches.

Attached Images

SW_M&P1948.jpg (24.4 KB, 23 views)

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I'm with her

I've replaced several barrels without any big problems. But I replaced M-15, M-28 and M-29 barrels with the same model barrels, just different lengths and one 15 that had a cracked forcing cone. Only thing to crop up was cylinder to barrel gap that was fixed with a sharp file and feeler gauge.
SWCA 892

The pin does not actually hold the barrel in the frame, the barrel still must be torqued in order to be stable in the frame. A pinned barrel in a non-pinned frame is not a problem, but if you get a pinned frame, you will likely want to machine a pin relief into the barrel shank. Getting the barrel-cylinder gap correct and getting the front sight into the 12 o'clock position with proper torque can also require machining of the barrel.

__________________
VCDL, GOA, NRA

Pinned or unpinned, if the barrel isn't properly torqued into the frame the barrel will turn. If the barrel does not torque up and the pin is installed you can easily move the barrel about 5 degrees or so either way,

If the threads in barrel and frame are both clean ( usually chase them with a tap and die) the barrel should start to snug up at 6 o'clock and be hand tight around 9 o'clock or a bit past. Then you need to clamp the barrel, and use something to distribute the force on the frame to finish tightening it. It does not actually require a lot of torque.

I made and use a frame wrench with inserts, but watch at around 3:40 to see how the performance center does it. Basically a padded fork that goes over the frame. Also notice they do it with yoke in place. I believed the yoke helps support the thin vertical piece below the barrel junction and helps keep it from twisting down. You can't install a K frame barrel in a frame with the yoke installed however. Unless of course you have a yoke with the cylinder tube removed in your pile of S&W jigs