I've shot several different 300 win mags models and from different makers. There's a lot a variables that lead to how a rifle kicks. Weight of rifle, design of the stock, recoil pads and some synthetic stocks vs wood. There's a lot to go through and I'm sure opinions vary. Some don't have much more kick than a 30-06 and some feel like you got a hold of a 460 weatherby.

The ones I shot that seemed pretty mild were:
Ruger No 1, Ruger 77 wood and synthetic the old molded stock. Remington Senedero, Remington 700 CDL, Winchester Model 70 wood stock.

The ones that kicked a lot:
Remington ADL synthetic, Winchester 70 synthetic, and the Weatherby Vanguard. Forgot the HOWA

Hope that helps a bit. I haven't shot the X bolt but the Browning A bolts seemed like a well fitting rifle but never shot one in a 300 win mag.