Have herd Ruger outsourced barrels but dont remember the years that where real iffy?
I aquired a used M77 in 7mag back in the late 80s and still have it today. It looks to have had some action/barrel work done to it as the blueing doesnt match. I about peddeled it again as it shot groups like yours.
Talking to an old timer he convinced me to try a couple of things before giving up.
#1 We freefloated the barrel, added pillars, bedded the action AND the first 3" of the barrel. This helped some as its hard to keep the center screw torqued just right without doing this BUT
#2 Relieveing the back of the tang really helped!
#3 The barrel is the worst fouling barrel I own and it likes it that way=Fouled (Just like my M77 243 sporter did from the same area) . Shoots rounds 4-30 great and then its time for some aggressive cleaning to get it clean so I can waste 4 rounds to get it dirty again
Properly fowled this unit will group under an inch with the old blue boxed Federal classic 140 grain factory ammo and back when I had a # of that real slow lot of R22 would shoot a lot closer to ½" with 160 Partitions and 162 Amaxes.
For some reason I like that rifle????
A new barrel might save you a lot of messing with it but everything I did is nice to have done to them anyway.