Well I just had one built earlier this year by Guntech.
I wanted a Browning rifle and I also wanted a .338 caliber, but not a Win Mag. I remember Browning had produced some 338 RUM's but they had been discontinued and I had not found one floating around, so I started looking through the reloading manuals for something of interest. Looked up a 378 Wby and decided that was the caliber I would go with.
Went into Island Outfitters one day in January, and out of the corner of my eye a little gold ring catches my eye, I ask to see the rifle it is attached to and it turns out to be a Browning BBR in 7mm Rem Mag with a Vari-X III 3.5-10 AO and sling, so I asked around (gunsmiths) about this rifle and a caliber change, most of them talked me out of 378 Wby and after talking to Guntech a few times, he had me convinced on a 340Wby instead, and that was great I bought the Browning and a box of ammo and blasted the box down range before the surgery began. Had to try it out before changing it up you know.
So there I was, found a beautiful hardly used safe princess and was converting it into an awesome 338 caliber, right what I was looking for in the beginning.
Here it is wearing a Vari-X III 4.5-14 X 40 AO, fixed in nickel Burris signature posi-zee rings and well some stainless weaver Winchester Model 70 bases. Also sporting a 26.70" Gaillard stainless barrel, free floated and bedded action, trigger adjusted to around 2.5 - 3lbs. The muzzle is a 60 degree target style crown, very nice. Shoots amazingly well. The magazine is a standard long action magnum magazine with some work to fit the 340 shells in, still holds 3+1.
http://i177.photobucket.com/albums/w240/b-ruddick/IMG_1567.jpg
http://i177.photobucket.com/albums/w240/b-ruddick/IMG_1546.jpg
http://i177.photobucket.com/albums/w240/b-ruddick/IMG_1568.jpg
I haven't thought to much about the next build yet, but that doesn't have to happen anytime soon, this 340 is my current carry all rifle and will most likely be for a very long time.
Added July 13th @10:13am; I guess this is more of semi custom build, but my first nonetheless.