Why don't you go with the 338 lapua case instead? same bolt head diametre less the belt problems.+ best brass available from the market .

ND

lapua brass brings you to the 510 whisper, but I suppose you could go a tad longer to get what you want

If I wanted to use a suppressor, and go subsonic (only), the SSK .50 American Eagle Encore barrel I had was fun to shoot. The little 50AE case looked so little with the long BMG bullets! Didn't have a suppressor then though, but the round was pretty accurate for such a big bullet in a little case!

I have a barrel from SSK for my encore, the 50 alaskan
I can move 700grn bullets at 1625fps that is 3650fpe and have loaded down to subsonic and have good results suppressed.
the brass can be purchased from starline.
I would consider this option for a 510 whisper

I have been playing with a 510 whisper on my Encore for a few years. It only weighs 7.5 pounds, so when using 950 grain cast bullets, it is punishing. I usually shoot surplus M2AP.

I made a aluminum 2x18 inch silencer for it a while back. It adds almost two pounds of weight to the package, so it tames recoil a lot. It typically shoots about 2 moa with the surplus bullets, a bit better with amax. The cast bullets do less well than the surplus. Recoil was enough to break two scopes, and damaged a Leupold VX3. It also ripped off the bipod adapter and the fore end. I made a barrel band to hold the fore end on. It soots better off of a sand bag than the bipod.

I have made my own brass on a lathe using once fired 338 lapua, but it was inferior to the stuff supplied by Michiguns to SSK.