OK, I have not been following your issue but bear with me. I've had a lot of experience accurizing an Omega.
1) What is that stock made of? I have on of the original laminate wood stocks, which is what I have accurized. Yours looks synthetic? That will make it harder to work on...
2) Is the action completely out of contact with the stock between the recoil lugs? It looks like a big cavity there.
So here is my issue with what's been done so far. Just my opinion, take it for what its worth
A gun's accuracy depends in part on how repeatable the things that happen after each shot are. By trying to shim the action to relieve pressure on the barrel, you are ruining the contact between the action and the stock. It may seem solid but, especially since you describe a significant angle and canted action screws, I'm pretty certain this contact is messed up. For certain, you are placing strain on the action.
If I were you, and you really want to fix this gun, I'd do the following:
1) Remove the shims and put it back together as it was supplied to you.
2) Whether with sand paper (if it works on that stock) or a power tool, carefull sand the barrel channel until the barrel is fully floated back to the front recoil lug.
3) Shoot a 200gr SW at 90, 100, and 110 gr powder for group. If it shoots well, stop. If not, go to step 4. The reason I recommend this bullet is I have tried it in multiple Omegas and it has shot well in each in this charge range.
4) Install action pillars. I bought some Remington 700 pillars and cut them to length with a hacksaw, but any aluminum tubing from the hardware store will work. Some have used those steel threaded pieces used to run wires through in lamps successfully. If you use non-threaded tube, you'll need to drill a hold to enlarge the current action screw holes out to the tube diameter, cut the tubes so they are flush against the lug on the inside and flush with the stock or slightly recessed on the outside (if recessed you can enlarge the hole slightly so the screw heads are recessed when inserted).Epoxy those pillars in, from the outside so no epoxy reaches the inside, and let dry with action screwed in tightly so it sets up in the right orientation. If you use threaded pillars, you'll have to screw them into the stock and drill accordingly for that. All depends what you use. The goal here is that you now have metal-metal contact and each time you screw the action in the screws will stop HARD on the pillars the same way each time.
5) Shoot as suggested above. If still not good, proceed to step 6.
6) Bed the whole action from the back of the receiver to the front recoil lug. I recommend ProBed-2000. I cannot give you exact instruction on this as it depends on the design of your stock. The ramrod channel can be an issue, but you use clay to fill in the parts you don't want filled like that so it's doable. Basically, you will grind out (dremel is great) at least 1/8" of material in EVERY place the stock touches the action except those shiny new pillars (including all around the pillars. You then fill in everything with epoxy to create a nice, uniform bed that conforms exactly to the action shape to lock everything in solid. Mine is so tight that the action can only be removed with two hands to pull the lugs straight up out of their beds. Any cant and it won't come out, it's awesome.
7) Shoot it again. If it still does not work, try 2-3 other bullets. If that doesn't work, your barrel is CRAP because you have fixed everything else that could be the source of the problem.
When I started with my Omega, it was a 1.5 MOA gun and POI changed with action screw tightness. Now I can shoot it sub-MOA to 200 yds and MOA to 400 yds and it will return to zero nicely even if I pull the action from stock and put it back in.
Nothing I have suggested can make anything works. No guarantee it will be better either but this is what you do to accurize the gun.
If you decide to go this route, PM me and I can help you some more.
