.38 WCF (Winchester Center Fire) is also known as the .38-40. It actually is not a .38 caliber, but is .40 caliber/10mm. The cartridge is the .44-40 necked down. (From a performance and ballistics standpoint it is similar to the .40 S&W.)
It's not a rare caliber, but it also is not common. The .44-40 was far more popular for the large centerfire in this model. And most people wanting a smaller cartridge for small game went with the .32-20, also chambered in this gun.
There are still some cowboy shooters who are shooting the .38-40, but they're in the minority. This cartridge appeals more to collectors.
<i>"A gunsmith told me that the old westerners liked to have a rifle that shot the same shell as their pistol so as not to have to carry two calibers of ammo"</i>
Was not much of an issue at first, because you carried a handgun in .45 Colt, .44 American, .45 Schofield, etc., plus a rifle chambered for a large cartridge like the .45-70, .50-70, etc.
But then Winchester came out with the 1873 lever action in .44-40. it became popular because it had moderate power and the magazine held lots of cartridges. Problem was if you carried a handgun you had to carry two similar sized but totally non-interchangeable cartridges, like .45 Colt and .44-40.
Recognizing that the two cartridges are very similar in performance, Colt came out with the Frontier Six-Shooter in 1877 in .44-40 so those with an 1873 in .44-40 could have a handgun in the same chambering and carry only one type of ammo.
Eventually both the Winchester 1873 and 1892 were made in .38-40 and .32-20, and Colt made handguns in these chamberings as well. The only chambering this is not true for was the .25-20. Colt did not bother to make a single action chambered for it.
I have a Winchester Model 92 in the same caliber, .38 W.C.F., but mine is much older (SN 95,XXX). I paid $35.00 for it many, many, many years ago. As the bluing was all gone and the stock not in the best shape I had it re-blued and the stock refinished about 10years ago.
Yes, I know, from a collector's stand point, I lowered the value! But as it was my gun and I had/have no plans for selling it I had it done as a Birthday present from me to me--lol.
Anyway, it sure looks great and before I had the work done I used to shoot it some and even killed a deer with it.