I've hesitated to comment here until I talked to my friend today who is THE M77 expert. He says the 7x57ST was only made in the 22" lighter barrel, same as the 30/06. Only early M77's to have the 24" medium weight barrel are the 257 Roberts, 25-06, 7mm RM, 300 WM and 338 WM.
I remember this as El Numero states it above. My cousin had a 257 Roberts with the medium weight barrel; I had a Roberts with the standard 22" barrel. We used both on piles of VT woodchucks,crows etc.
But lots of funky stuff went on at Ruger when the M77 first came out. One shop in our area had a tie-in to Bill Ruger or someone at the plant.Bob Chatfield-Taylor occasionally wandered in there and was a buddy of Bill Ruger. Feel free to connect dots. I could only surmise
As a broke college student at the time I could not afford some of the uncatalogued goodies that showed up but saw a lot of them; they included early runs of 7x57,257 Roberts 256 Newton(! ! yes I saw them in the flesh),and 416 Taylor (3-4 as I recall),250-3000 and some others I can't remember. I was offered a Newton but could not afford it.
So I would not be surprised if a medium barrel 7x57 popped up from somewhere,although I don't recall any. Many guys at our club bought 7x57's but they were all 22" light weight barrels.
