What JB said, and per Bigstick on OAL, if an issue there is always the Proven 210 PT and 210 TSX, HOWEVER, I ran 225 PT vs 210 for more energy, BC/SD, and only giving up 2" drop at 400 w/a 200 zero.
Ran a 1.5-6x 4200 in Colorado and it was a heavish scope, as my 8lb rifle sans scope was not so generous for any extra. Later had a 2.5-8 for a Texas hunt where I pole axed a nice 8 point, and then a 6x42 for local hunting, the latter I did most of the load testing, everything was 1/2" from 200 BTs, to 225s, though speaking of OD, mine was a bit thick, as I told Hart .050 over either sporter or Mag contour, a mistake. Mag contour would have been about right, and 22 if did again.
My former 22" SS Ruger 350 had a BOOM, I figure a similar capacity/expansion ratio OKH should be similar but a little closer to the ears.
A guy on another forum chopped his 338 WM from 24 to either 20 or 21, as I recall, and it lost little speed. I chopped one I had to 22.5, and as a mag contour it did well. My 23 was more than needed on my OKH.
It will handle well, if balanced. A 4x33, 6x, or small variable like the 2-7, 2.5-8x is what I would be looking at running. Never been happy mismatching a bulky heavy scope atop a rifle not welcoming it.
Never much to disagree on Big Sticks Calculations, but I question if one can make a shot with a flyweight OKH at 1K, so not sure how it applies, nor if the OP has plans for LR.
The biggest shock to me is not the 20" or OAL etc., it is the re-boring to 338 in a contour that light. So long as safe, no problem. It should heat fast. Cold bore first shot is key, so if stable, should be fine in the field. My 700 was chambered for 250s just b/c, and having such a deep throat, the OAL was very long and mag compatible, and still shot bugholes with 200 and 225s, so no regrets on how it turned out.
My biggest complaint was choosing TOO heavy a contour in my younger years, and then having the bolt handle fall off on the first shot after that Colorado Elk trip. Had I taken an Elk, it would have been with ONE shot, and the rifle would still be wrapped around an Aspen on some Mountain side!
