Although I have no experience with the m77, I do have two liberty number one rifles in 7x57, and have owned others of that vintage and even earlier. I have found all of them to shoot very accurately. I shoot nothing but handloads, but have put quite a variety of loads through these rifles. As one would expect, some rifles like some loads better than others, but I have never had one that would not shoot to my liking, and none of the rifles were inaccurate with any of the loadings I fed them. I have fired lots of the lighter 140gr bullet loads and they have performed as well as the heavier bullets. Assuming that the M77 was chambered to the same specs as the number one of that era, I would not have any hesitancy in purchasing one of the former. It is an outstanding caliber - probably the best all-around for N America.