Is it a mkII or a tang safety 77? There is no way of knowing how the rifle will shoot without firing it yourself. Over the years, Ruger has put out some very good rifles and some pretty mediocre rifles. I know they outsourced there barrels for a period of time, and that didn't work out too well. They have an action design that is supposedly time consuming and difficult to bed. I am pretty sure that many have a pressure point where the stock will contact the barrel.
I'm sure, at the very least, that the gun will be hunting rifle accurate. I've heard of some that would do a 3" group at best and others that would bughole. I got lucky with mine. It was an 84 model year production 77 with the heavier contour barrel in 308. I relieved the pressure point, put on a decent scope, and worked up a load for it, and it will do around an inch all day long with no wandering zero. 400 Does not sound like a bad price. They are well built rifles and can take abuse. They may not be refined, but they work well.