The process S&W has used for several years now for rifling center-fire barrels is EDM, Electrical Discharge Machining. This is the same process used by Magna-port to cut recoil reduction ports in barrels as it leaves a smooth finish and no burrs. It is done submerged in a liquid bath and leaves the bore exceptionally smooth but with slightly rounded corners instead of sharp square ones as the immediately preceding broaching system. They have been using the process for many years to made forging dies for some fairly complicated parts used in their guns. What I am certain of is the safety/decocker levers for the automatics. EDM was used to machine the recess in the forging dies for these parts that allowed the part to be forged including the grooving in the surface of the lever.

Unless they have discovered something fairly recently the .22 barrels are still broach cut as the bore is too small for EDM.

One advantage of the EDM rifling process is barrels do not have the so-called frame choke which is common with broach-cutting.

S&W did have dimensional control problems with early EDM barrels. Whether it was duration or voltage variations were the culprit some barrels came out with some odd dimensions. Some were a little tight and some were quite oversize.

I had an early EDM rifled .44 Mountain Gun which had normal cylinder throats (ball-seat actually) but the groove diameter was .435. And, yes, I have the proper tooling to accurately measure a 5 groove barrel slug if you wish to argue this point. The thing wouldn't shoot in a bucket with cast bullets. After lapping a mould so it would throw bullets at .436, a custom lubri-sizer die for .435 (sized .4355), and reamed the throats to .437 it actually shot very well. What a pain! To accomplish this also required reaming the brass as deep as the bullet shank seated using a .435 reamer in as-fired cases which removed about .0015" from the case wall. That was necessary so the ammunition loaded with the .435+ bullets could be chambered. Then I sold it. Now the cases that were reamed are un-usable as they are so thin that none of my sizers will reduce it enough to hold a .431 or smaller bullet.