Lots of companies make 21 barrels with ordinary land and groove rifling. If the bullets are hard enough, and not too fast, and you are diligent about cleaning before you shoot jacketed bullets again, people do use the stock barrels.
But for all the work, it's still easier and probably safer to just spend a hundred or so bucks on a new barrel.
Lone Wolf Distribution or Distributors sells their own in-house barrels and sells most of the other offerings as well. I've had very pleasant interactions with them, including one of their top guys calling me back and forth a couple of times to get a 27 40-9 barrel tuned up the way I wanted it.
Specifically it didn't like the Fiocchi Extrema 115 grain XTP load, the shoulder was full-caliber and it engaged the lands right away and wouldn't let the gun go fully into battery. Took a smack to the rear of the slide to get it shut, then shooting it out. Wrestling with the slide (which wasn't moving) of a chambered Glock seemed like a much worse idea than just shooting the cartridge out. I sent them the barrel with a couple of the cartridges in question and less than five days after I shipped it the thing was back on my doorstep (Maine-Missouri and back from Monday to Friday) in time for the weekend range trip.
Cannot beat that level of service from any company. I think the firearms industry spoils our expectations for companies, honestly. I called Aerobie and asked if could buy a small parts kit for their Skylighter, and the guy who answered sounded baffled that someone would ask for such a thing. Gunnies are a special breed.
This gun is actually designed for, and has a counterpart in, 10mm Auto, a much higher pressure and recoiling cartridge than the .45.
