Re the original question in this thread:
I own a WB MK V in 257 WBY Mag. And it’s an ultralight. When I first shot it that ultralight would literally leap in the sandbags. The whole thing would jump up and back, that’s what 75 gr of powder does in an ultralight. So I put about 4lb of lead shot in the butt (did it so it’s removable) and made it a regular weight hunting rifle. It doesn’t shoot the greatest, ok it doesn’t shoot very good at all, the best I can get out of it is 1.5.” And I’ve tried all kinds of things, change the barrel rest in the fore end, free floated it, bedded the action and the first inch, then removed the first inch, even had half inch cut off the chamber end of the barrel and re-chambered to a more conventional throat length, all to no avail. Most weatherby’s shoot really well, but mine doesn’t.
That’s my story on a WB. But why would you want to buy a Mk V and chamber it in an anemic round such as the 6.5CM? That belongs elsewhere such as a savage or a CZ. Thats like putting a Chevette motor into a Cadillac. Save the Weatherby’s for the WB cartridges. Again, that’s just my thots.