Here is a review I wrote on the Forum a couple years ago while researching this caliber. Hope it helps.
Solving the 38 Single Shot Accuracy Mystery
I have been struggling with a 38 Single Shot barrel I had acquired through a source that purchased a large lot of factory leftover stock years ago. These barrels had never been issued and were in the white without serial numbers, but had the proper barrel rib stamping for a Model of '91. I purchased a 10" barrel in, what was advertised as 38 S&W. This source had all calibers originally available at the time, but I knew that the 38 barrel was the most uncommon caliber out there, so I bought one.
That barrel came from Poppert's years ago. It was said that they were one of the companies that bought out some of the remaining stock of single shot barrels and parts many years ago. I ordered the new-old-stock 38 Single Shot barrel in the white to go with my Model 1891 SA revolver. Shot a lot of 38 S&W ammo in the gun without much accuracy until I noticed that the chamber was quite long. Measuring it I determined it matched the 38/44 case exactly.
I called Poppert's for more data and they stated that all barrels were sold as they came from the factory and offered to trade it back to them for a short chambered 38 S&W barrel, but I said no thanks, I'll keep it. My assumption is that somebody in the S&W factory did some experimentation and modified the chamber to take the long brass. Maybe did some testing, but never pursued it further.
I cannot validate any of this information beyond what was told to me, but the results of my recreating the original loads, was that target shot at 25 yards.
I had a nice Model of 1891 factory target revolver, 38 S&W, that I had received from a SWCA member and thought that barrel would complement the revolver. After receiving the barrel, I blued it and, through the assistance of a few more members here, I acquired and/or made parts to install an extractor, sights, and put together the Single Shot. On my first trip to the range, plus several more, I could not come up with a load that would hit paper at 25 yards and very inaccurate at 50 feet. Trying several different types of bullets, powders, and crimp styles, I saw no improvements. As I was cleaning the barrel recently, I finally noticed the chamber seemed quite deep, so measuring the chamber I found it to be much longer than a 38 S&W round. Now thinking it might have been bored out for 357 brass. Loaded up some 357 Mag cases with .360 bullets and they would chamber easily and still seemed short, plus there was no improvement at the range. Was about to give up on the SS barrel, but a very learned member (Ralph) suggested that I check the chamber measurement and compare it to a 38/44 Target case. As it turns out, the chamber was exactly the same length as an old 38-44 Target round. The original cartridges were loaded as follows" The 38-44 is a special target cartridge containing 20 grs of powder and 146 of lead either self-lubricated or grooved bullet. Bullet is seated even with mouth of shell. Penetration 6 7/8 in pine boards. Gallery charge, 6grs of powder and 70gr round ball loaded in same shell.
In order to reproduce the ballistics of the original caliber, I acquired 50 rounds of 357 Remington Max and cut it down to just under 1.5". Used a 158 grain gas check SWC. The reason for the selection was that the bullets dropped from my mold at .361", just what I needed. I loaded as specified with BP and shot over a chronograph and got around 700 fps. I then worked up a olad using 3.2 grains of Unique and filled the case with Puflon. Velocity averaged 661 fps and accuracy improved dramatically at 25 yards. Now I am onto something here and look forward to loading more ammo to shoot at longer ranges with different powders and bullets to further improve accuracy.
Pictures are of the assembled set that I had shared when I first put together a case for the set. The chamber shows no sign of ever being bored out, so am wondering if it was something the factory may have played with during the production time of the 1st Model Single Shot? If so, I might have the only 38/44 Target barrel out there???? Just another fun adventure with a S&W.
