I would go A, because it seems like a waste to buy a rifle like that, and already tear it all apart. Shoot it have some fun,where it out , then make it into the 7/300 or 338 something that you may like .
You should go with "F"- none of the above. Take it and have it reamed to a 30-06AI and shoot the 185-215 Berger. Make a heck of a 1000yd deer rifle or an 800yd elk gun! Not to mention you can get Lapua brass. That's a bonus in itself!!! If you can knock elk down to 925yds (it was on a long range hunting show... don't shoot the messenger) with a 6.5-284, a 215grn bullet at 2700-2750fps will surely knock an elk over at 1000yds. It would have to be a sure shot though (I know, you need and uber magnum to do that in the only prescribed bullet diameter of .338 or bigger) and you would want to be confident in your abilities that far. Just a thought.
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Anything but a .280AI or 30-06AI is going to require action/magazine work of some kind and a magnum would require the bolt face being modified too. A 30-06AI will probably only give up 100fps to a .300wm but require custom dies and fireforming. I would probably go with option A just because the recoil difference between a .300wm shooting 210's, 215's, or 230's and a .338RUM/Edge/Lapua shooting 300's is pretty significant. If your recoil sensitive at all the .338's can be a handful unless the gun is pretty heavy. If recoil doesn't bother you and you can pack a heavy gun then the .338's would be the best elk medicine.
Right now the gun has a single shot follower so it wouldn't be to difficult to switch to 300 win, also my smith said he wouldn't have to set the barrel back and that he could just ream it. Will 230 gr Bergers stabilize in a 10?
Yes they will. If it's a single shot you could also do something like I shoot, a .30-8mm Rem. Mag. I get about 150fps over a .300wm with 210's. I use 8mm Rem. Mag dies to full length size and a Hornady neck sizing die to neck size when I have to. Mine is set up with a tighter neck so I get several loadings without having to size the cases at all. Just knock the primers out, put new ones in, fill with powder, and seat the bullets.