A LOT of current handgun manufacturers are turning to various means of heat treating barrels to increase the life of the barrel (and reduce warranty claims) these processes known as Tenifer, Melonite to name two that use the salt bath for treating, and nitriding as well. The salt bath hardened barrels are put through a much more thorough process than the surface treating like case hardening, they take a dip in a 1500F bath and are soaked in it for a specified amount of time. This often results in a barrel that's hardened all the way through, not just the surface.
Suffice it to say that carbide reamers are the only tooling that will successfully "throat" one of these barrels, that is to cut some smooth freebore ahead of the chamber, and push the leade-ins of the rifling farther forward to allow for chambering boolits seated to the published COA in load data, instead of being forced to seat down farther in the case so the gun will function.
The downside of using carbide for this is that the carbide reamers wear VERY quickly, and after only 10 or 12 barrels they start cutting slower, cutting smaller, not as smoothly, and they need resharpening. Let's say you custom order a throating reamer and you wait 6 months for delivery, and cost is 3x what a HSS reamer costs, and it only does 10 barrels before it's time to have it sharpened, you come to the realization that every time you use that $300 dollar reamer, it eats up roughly $30 worth of the cost to throat a single barrel. You send it out to have it sharpened, it costs in excess of $200 for this, plus a 6 month wait, only to get a new edge on the flutes that will be toast again after 10 or so barrels.
It is an expensive and time consuming game to stay in, in some cases it is cheaper and much more practical to source an aftermarket stainless barrel that can be throated to your heart's content with HSS tooling, for not much more than the cost of having a hardened barrel throated. It also gets you out of voiding a warranty by modifying the factory hardened barrel.
There is no winning this battle, carbide vs. salt bath hardening, you can't even break even. And there are some barrels that the carbide reamer won't cut, you can and will seriously ruin the cutting edges trying to throat one of these case hardened barrels, which in fact is MUCH harder on the surface than salt bath hardened barrels.
To meet the need for throating these barrels, I would have to invest in 2 or 3 carbide reamers so that I would have one while the others are out getting sharpened, the cost now hovering around $1,000, I could not offer the service at an affordable price point, as the cost for labor would be as much as the cost of a stainless barrel.
After wearing out several carbide reamers, not willing to forego the cost and time involved in getting them sharpened, I have been forced to back away from throating the hardened barrels, too much of an uphill battle.