Looks like a nice honest and clean M-1873, (third model), Antique rifle in the .38 wcf caliber. Not sure what the three engraved, yet nice looking, "M.S.W.", stands for, if I got it correct. It's also nice to have the letter with it. No mention of the 3 engraved letter on the brass elevator, on the letter, as you mentioned.

Nice find!

Thanks for sharing.

Tony

There are some very well done scrolling initials inscribed.  Nothing on the letter. There is a possible story, but I’d like to hear the experts opinion…… 

Bert H. said

Zebulon said

Bert H. said
It is critical that the 351 cartridge is reloaded to factory specifications.  The blow-back action will not function properly with loads that are too light, and if too heavy, they will damage the action (buffers).
Bert
  

Bert,  do you know whether the 351 was intended to headspace on the case mouth or the vestigial rim? 
  

While I do not positively know, I highly suspect that it head spaces off of the rim.
Bert
  

I've since had a closer look at the chamber on mine and there's no "bullet seat",  just a tapered leade, so there's nothing for a case mouth to headspace against. 

The "semi-rim" concept was devised to [A] allow cartridges without a shoulder to stack and feed reliably from a straight-line box magazine but [B] still headspace on a vestigial rim. It does not provide best accuracy, which is better achieved by a rimless case that headspaces on its case mouth against a 90 degree "hard stop" milled into the chamber. 

A classic example of the difference is Colt's Super .38 Automatic pistol cartridge, which is semi-rimmed and was ( and still is) chambered in a commercial variant of the Colt Government Model pistol and in the steel-framed Commander.  The barrels of these pistols were chambered to require the cartridge to headspace on its tiny rim, resulting in variable cartridge positioning. For Decades Super 38 pistols were  notoriously inaccurate compared to the ,45 ACP guns, although sufficiently accurate for close range combat. The Super .38 is powerful enough to give the .357 Magnum a close run.  Lawmen and gangsters bought it for that reason during Prohibition and later. Particularly in Dallas. 

Eventually, several gunsmiths - notably John Rollins and Richard Shockey, discovered that Super 38 barrels cut to headpace on the case mouth like the .45 ACP were capable of being tuned to match grade accuracy. Irv Stone commercialized the idea and his Bar-Sto Super 38 barrels were all the rage in the Seventies and Eighties. 

Once Colt's came under management that cared about what it was doing, Super 38 automatics coming out of Hartford had factory barrels cut to headspace on the case mouth. They give good accuracy out of the box, at least equivalent to the .45 versions of the same gun. What a talented pistolsmith can do with either caliber is astounding (to me.)

Zebulon said

Bert H. said
It is critical that the 351 cartridge is reloaded to factory specifications.  The blow-back action will not function properly with loads that are too light, and if too heavy, they will damage the action (buffers).
Bert
  

Bert,  do you know whether the 351 was intended to headspace on the case mouth or the vestigial rim? 
  

While I do not positively know, I highly suspect that it head spaces off of the rim.

Bert

After locating six spent OWS cases and four spent Western cases, I resized but did not deprime, all ten, using the new Redding sizing die, after chamfering and lubing with Hornady sizing wax. I expanded the cases enough to receive the brass-plated 180 grain, .351bullets from Grafs, and seated them to a depth of between 1.892 and 1.898, depending on exact case length but making sure all were at or below 1.900.  After wiping the sizing wax off, I tried them in the gun until my arm wore out. 

My mag loader was downstairs and three rounds was all I could et into a 5-round magazine. Cutting to the chase, every round that made it into the chamber was successfully "fired". Manually compressing the operating rod swiftly and to its limit, to replicate the normal semi- automatic loading and ejecting cycle requires strength and endurance that, in my case, faded rapidly.

Ejection was never  problem and I'd placed an HD orange bucket that caught most of them.

Whenever I failed to get the bolt back to fullest compression, it would ride over the top round in the magazine instead of stripping it off the follower and chambering it. However, early in the exercise, before my breakfast Wheaties gave out, it picked up and slammed home rounds with commendable enthusiasm. Operating under actual recoil, I don't think feeding will be a problem. 

I don't want to shoot the gun a lot until I can check the condition of the buffer. In that regard, I am pleased to see there is a ready supply of new buffers for the 1907, at least, on eBay, made of various modern polymers that likely work better and last longer than the original Vulcanized rubber or some fibrous material. Some of the new ones look like Delrin and were obviously made on a 3-D printer. 

I'm open to any crafty suggestions for a fixture to tame the mainspring while I replace the buffer. I think Steve Gabrielli had devised one.

The

Zebulon said

Bert H. said
It is critical that the 351 cartridge is reloaded to factory specifications.  The blow-back action will not function properly with loads that are too light, and if too heavy, they will damage the action (buffers).
Bert
  

Bert,  do you know whether the 351 was intended to headspace on the case mouth or the vestigial rim? 
  

Bert H. said
It is critical that the 351 cartridge is reloaded to factory specifications.  The blow-back action will not function properly with loads that are too light, and if too heavy, they will damage the action (buffers).
Bert
  

Bert,  do you know whether the 351 was intended to headspace on the case mouth or the vestigial semi-rim? I have not seen a drawing of the 1907 chamber dimensions but have been told there is no machined step on which the case could be headspaced; only a tapered leade. 

Bert H. said
It is critical that the 351 cartridge is reloaded to factory specifications.  The blow-back action will not function properly with loads that are too light, and if too heavy, they will damage the action (buffers).
Bert
  

Bert,  do you know whether the 351 was intended to headspace on the case mouth or the vestigial rim? 

Zebulon said
For comparison, here's the later "police rifle" style finger piece. The bolt hold-open procedure is the same.l mi
  

I like the user friendliness of the finger hook.  The usual style allows the index finger - especially a cold or wet finger - to slip off very easily.

The ammo I had at our range session that wouldn't allow the sear to release was Old Western Scrounger [the custom loads in the skunk picture box.]  It was made from 357 Max brass and -- thank you, Bert for posting the official dims  -- i'm about to measure some specimens against those specs. I have already measured a couple against some vintage Western cartridges and couldn't see anything really out of whack. I had thought the Max case rims might have been too thick or insufficiently turned down to the WSL's semi-rimmed diameter. Not that I could see. 

Now that I have a set of dies and some plated bullets from Grafs, I am going to make up some dummies from fired Western brass and the plated bullets. I'll use those to function check the gun. I should mention that i fired several of the OWS rounds in another, older Police Rifle version 07 I used to own, without incident. So it may be my present rifle that's faulty.

For what it's worth, I've attached a closeup of a 1907 operating rod with the older disk rod tip/finger piece, annotated to describe how the bolt hold-open function is achieved, for anyone not intimately familiar with the WSL series. 

The 1907 seems to somehow peculiarly exhibit "Winchester-ness" -- like the forearm latch assembly of the Model 21 and the bolt removal and reinstallation process required by the Model 52. Nowhere else but New Haven.