Re: Help! Gun will no longer group at all!
It might be caused by all the things listed above...........or not. I shot the barrel out of my old tried and trued commercial Mauser 98 in 30-06. Sounds just like what you are describing. Groups were tight, then started to have a wild shot or two now and again that I figured must have been me. Then all at once it started shooting 5" groups. I went nuts trying to fix it. It must have been the powder lot, of primer lot, or.......
Then it must be that the scope went south, so I swapped scopes.........
I don't know how many times I had it apart and under the scope looking at every detail. That rifle got a better cleaning than any rifle ever has - several times, and nothing changed the group one bit. I confirmed that it wasn't me by printing sub-moa groups with my other rifles.
Look at everything everybody else has recommended - all of these things can affect the groups. But in the end, you may be right that the throat is eroded badly enough to cause what you are seeing. The .280 isn't as bad as some about burning barrels, but it does hold enough slow-burning powder to erode the throat faster than some other calibers.
If you like the Ruger, then keep the Ruger. Your accurate rifle didn't just become inaccurate because it just discovered that it said Ruger on the barrel. I've had my butt kicked in competition with rifles and calibers that I wouldn't have given you ten cents for before the match. The proof is in the shootin'.
Attitude is EVERYTHING!