I am joining this late...

I think it is bedding. If you think about it, any bedding problem in a 77 is going to be magnified by that dumb angled screw (okay, Bill Ruger was rich when he died so he wasn't that dumb). It is going to cause the action to flex. The advice someone gave about tightening the first screw will reduce this potential.

If you rebed it, get the lugs lapped. Uneven lugs (which is what you get if the action is improperly bedded) will cause flyers like this.

I don't think the barrel heating is an issue as you described it. I shot 20 shots today with a .300 RUM; the barrel was warm, but the bullets were all true at very long ranges. A rifle that completely throws bullets around if it is slightly warm is not worth hunting with, IMO.

Thanks for the good advice guys. Several people have recommended Roger Farrel in Fayetteville. That is about an hour drive so perhaps I can take it to him one afternoon.

I have never seen a full length bedded rifle. Does anybody have an opinion on this? As long as it improves the consistency of the rifle, I would be happy.

teal325, do you have any contact info on Greg Tannel?

I have never seen a full length bedded rifle. Does anybody have an opinion on this?

For what it is worth, which admiditly might not be much, my first choice is always to full bed a rifle. To date I have never had to free-float one yet to get what I thought was acceptable accuracy. Sometimes the bedding may need to be scraped a tad, but floating was never needed. My Wife has a 7X57 rifle with a #1 Shilen barrel on it that will ocassionally flirt with one inch groups at 200 yards and they are a pretty slim tube so I am sure that it works to full bed.

I do admit to also having more trouble with Rugers which I also blamed onto the angled guard screw. However even with that I have gotten them to all shoot into one group. If it was mine I would certainly try the full bed method making sure the action and barrel were both bedded properly and not binding anywhere.

Ruger's idea was that a properly bedded action is pulled back and down into the stock, seating the recoil lug and it's stock abutment perfectly. It works very well, the key is "properly bedded". If the tang area hits wood before the recoil lug is seated, it will bind the action and not shoot well. The unique Ruger design, is no better, or worse, than any other, it sill has to be properly bedded, it just takes a different approach.

I think it could be due to one of several things:
1) the barrel has stress in it,
2) the action has stress in it
3) the barrel wasn't screwed into the action correctly.

The fact that if you wait to fire a second group and it does the same thing tells me it's heat related. In all 3 of the possible cases, when the gun heats up the group will walk.

#1 & 2 might be cured by having them stress relieved, #2 might be cured by bedding, #3 might be cured by blueprinting the action.
So, try bedding first, stress relief second and lastly, either get rid of the gun or pay big $$$ to have the action blueprinted.