. . . . . .You can try to experiment with different tensions on the cross screw and, in some cases, it does make a difference but any accuracy gained is usually an accident and not a scientific adjustment. . . . . .
  

I just went thru this procedure with the barrel band, “tuning” it to my particular ammo . . . .(CMP/Eley standard velocity)

After turning the screw clockwise . . . .1/4 turn at a time . . . . I fired 5 rounds at each quarter turn.

In my rifle, the “tuning” paid off!

thank you

Randy

You're correct in you're assessment on some of the original stocked 52's. But the OP, (MFoster), who bought serial number #13 at Auction, and is going to post pictures here, already stated that the stock has some additions to it, that had me wondering. 

Seewin, who forgot more about the Winchester M-52's than I will ever know, IMO, stated that he saw some pictures, on the Auction site, of the said rifle, and that the stock was a Custom made stock, which to me explains the extra added things that the OP, was talking about. With no finger groove on the stocks wood forearm, it tells us that this stock is not original to the rifle. 

Still looking forward to the pictures, and as many different angles as possible.

Tony

Henry Mero said
This one is all nickel 
  

Where's the slide to pump it?

Hazer1958 said
I have a model 677 that was originally  my mother's. My father had sights put on it probably  45 years ago not knowing  it was a rare gun. What would be its value now?
  

No possible way for any of us to answer that question without first seeing several clear detailed pictures of it.

Bert

Goatkeeper said

Bert H. said
I personally would not do anything to it other than give it a light coat of oil on the steel and wood furniture oil on the stock.  That old rifle earned its keep and its "battle scars" and should keep them.
Bert
  

Thank you Bert!
I try to narrow the production period. 
so far I learned, that the markings esp. about the patent and calibers may help. Since it is no „extra long“ it should be before 1920. Is there any hint to pinpoint it closer?
Since I like to shoot my firearms, i consider to give it a try with .22 short. The rifling is visible, but the first part of the barrel seems a bit rusty. 
do I risk to get a blocked barrel?
 
Best regards from Switzerland
  

The "Extra Long" was added in 1914.  That indicates that your Thumb Trigger was manufactured sometime in the 1904 - 1913 timeframe.

Scrub the bore with solvent and a copper bore brush, then go shoot it.

Mike

It could just be the light in the image but, if the buttplate is likewise plated, I've seen that configuration catalogued as the "half nickel" Special Order Feature. I assume there could be a "half Silver" feature as well -- or anything else your heart desired and your pocket could stand.