This explains a lot.
I developed a sour taste for Rugers early on after picking up a tang safety .300 Win Mag. It didn't group so much as it patterned. Four inch groups! I tried bedding it and had a smith work the trigger over and it shot slightly better, but still not even close to acceptable, 3-3.5 inches at best.
I managed to trade it to some guy ditching a tang safety .270 because it wasn't MAGNUM enough or whatever, that one was fairly erratic as well. I mean, unless you liked stringing shots. Which was a shame, because I loved the action design and "feel". And that one was bolted to a decent plank IIRC.
I'm now reconsidering trying the Hawkeye model for my next purchase but was always leery after my initial experience. Good to hear that there may have been a reasonable explanation for the staggering lack or accuracy, because the M77 is something that I really want to like.