That ammo is mil-surp, and it's 30 years and 7 months old, right now. You can't guarantee that it was ever stored properly, at all, and the brass isn't schit by now.
Get some NEW, good ammo, shoot it, and see what happens. I'd be curious.
Also, that was the first round - it's brand new. You need to run a few through it to see how everything functions. That first round is kinda like putting ten targets up, firing one round apiece at them, hitting the dead center on one, and saying "My rifle is dead nuts ON!" You need to see the variation in more rounds fired, before you can really judge what the rifle is doing.
My $0.02.