Depends on which "M 77" you are asking about.
Early tang safty M 77s - despite the extractor were actually push feed, but had a decent trigger.
The next M 77 (the MK IIs) were controlled round feed had notoriously heavy triggers and early models were know to often have dubious quality barrels.
Later model 77 MK IIs had better, consistent barrels but still had $hitty triggers.
The new M 77 Hawkey has the better barrel (free floated), and a nice trigger.
One other major difference. The early M 77, and the M 77 MK II also had a stock/barrel combination that that included a pressure point on the forend.
Now in full discolsure, I own 3 Ruger M 77s. One Hawkeye and two MK IIs. The Hawkeye shoots great and I love the new trigger, but despite the fact that the barrel was supposed to be floated, I had to remove a little wood from the forend to actually "float" that barrel. It is a 375 Ruger and will shoot all day into 0.75 to 1.25 inch ( 5 shot groups) if I do my part.
As to the MK IIs, I had to float the barrels on both the 30-06 and the 25-06 to get them consistent. They would shoot 3 shot groups "ok" but start to wander on the 4th or 5th shot (I suspect because of the pressure point and barrel heating). Floating the barrel on the 30-06 was sufficient because the factory trigger was right at 4 lbs. (not 3 lbs like I prefer but 4 lbs was OK and not worth the $175 to replace).
However the 25-06 factory trigger was was close to 7 lbs and that is not fun for a rifle like the 25-06. Eventually replaced the trigger with a Timney and that ( with the floated barrel) brought the groups down.
So in answer to your question, Yes there are a lot of Ruger 77s on the used gun racks -- I have noticed them myself. If it was my money I would prefer to buy a used M 77 Hawkeye first, then a late model MK II second -- to get a better standard barrel and would expect to have to float the barrel and replace the trigger on the MK II - worst case. Just MHO.