I have one. A very fun gun to shoot. The peep sight is basically worthless.

 

I also have one and no markings on the sides of the receiver, still a good shooter but the extractor is worn down and needs a dab of weld to build it up again.

 

It's a model 6, actually if your receiver is blued I think it would be the Improved model 6. I just sold one that had a case colored receiver and it was clearly marked on receiver. I have had a few, some were marked and some weren't. Just reread your post and you say its case colored, so in that case would be the first model six, the model six improved were all blued.

 

Have one also...fun little gun.
One of the few, Frank USMC RET

 

Thanks

I think by its features from what I have read it is a first model. 20 inch barrel, rudimentary rear sight on the barrel, short forearm and integral to the receiver trigger guard....And I do not think the peep sight was an option on the New Model..Just stuff I have read in the last day..Those little Peep sights may not be much..But it is probably worth more than the Rifle itself,LOL

What year it was made is probably going to remain a mystery. It has no date codes on the barrel as some say the later ones did..

Mine has a nice bore and extractor, despite the outside worn appearance..