Sears Model 53

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I have a question, I know that winchester made this rifle, post model 70 and it is in good condition. I looked everywhere but still can't find this gun.
Sears Model 53 in 300 Win. Mag. mod no 273.1870
The model 53 was only offered in .243 .270 .308 .30-06
not .300 win mag!

 

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Sears T.W. 73, 273.1850 Winchester NM 70
I found this at numrich it should be a model 73.
Is there a mis-print somewhere or is it a rare firearm?
What does NM mean?
Any help would be greatfull.