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.

Finding .351 bullets is the easiest thing to do.  

steve004 said
.351 SL brass presents a challenge.  Mainly because the big ammunition manufacturers haven't made it for many years.  Handloaders have used a variety of methods to make their own.  In more recent times, the .357 Maximum and .360 Dan Wesson seem to be the most workable candidates for a parent case for alteration.  For those on a budget, .223 cases have been made to work.
I have fired .351's (and .32 SL's and .35 SL's) while standing in grass.  Wow - these cases have a knack for disappearing quick!  Here's a tip:  go back at night with a flashlight and you can find the ones you missed.
  

I’m planning to take my $40 metal detector with me.  It’s not the best, but it works. The kids play with it and for things like this, it will save you a lot of time.  

I have fired .351's (and .32 SL's and .35 SL's) while standing in grass.  Wow - these cases have a knack for disappearing quick!  Here's a tip:  go back at night with a flashlight and you can find the ones you missed.

Bert

Jeremy P said
What ammo were you using? A friend is trying to get his to function and we think it's ammo. Do you have a set of calipers by chance? Would like know overall length of the cartridge 
  

https://winchestercollector.org/forum/winchester-rifles/the-power-of-the-351-sl/

https://www.buffaloarms.com/winchester-highly-finished-arm-bokwhfac.html

Michael - that would be very cool if the serial numbers were included in the descriptions but alas they were not.

There were over 50 Model 1892's, the majority of them quite special.  There was a musket, a cutaway carbine, a cutaway rifle, a whole lot of Trapper carbines, in all chamberings, and quite the variety of barrel lengths - starting at 12 inches - and including 17 inch.  Also an engraved Trapper, a "MGM Movie gun", a smooth bore short rifle, a 14-inch octagon barrel short rifle and then one of my favorites, a 15 inch round barrel short rifle with full magazine, pistol grip and shotgun butt (pictured in the Winchester Handbook by Madis). 

It would be helpful for me to have your attitude about Trapper carbines.  That would have spared me much envy-induced agony.