The man already said he's an experienced rifle shooter. First thing I'd do is get some dent glass and good mounts. If the rifle still shoots bad I'd return it. Without being able to see your groups I couldnt tell you whats wrong but even if it is the rifle you can then buy a better one and already have the decent glass to put on it.
I may go thru life wearing old jeans and khaki but my rifle glass is always first rate, as are my rifles, "just like a redneck". And like a redneck I'll skimp on eating before I'll skimp on my rifle/glass.
I agree with you about the glass, and I saw that he's had some experience with shooting. He definitely doesn't come across as a beginner.
Even so, he did ask for input, and the advice given is relevant to experienced shooters. I know LOTS of very experienced shooters and hunters, and I've seen most, if not all (including myself) make very similar mistakes, so I hate to rule anything out.
If I had to spend money on one aspect of a scoped rifle set-up, at the expense of the rest, it'd be the glass for sure. In reality, there aren't many modern rifles out there that shoot worse than the VAST majority of even very experienced shooters. In my experience, unless it's bargain-basement stuff, the hardware will generally out-perform the shooter. That said, I've seen guys that could work magic with crap, and guys that shot like crap with the best stuff out there. In the end, it generally comes down to the jerk on (or behind
)the trigger. You can't buy skill, experience, or technique, and that's almost always where the real problems lie (even though we all like to blame the equipment first).
If he's looking to just swap out his new gear for different new gear, I'd agree, the scope is the most logical choice.
Then again, that may do nothing, in which case he's back to trouble-shooting. I prefer to trouble-shoot first, and have found that to be quite successful.