Yes I have a 257 as do three of my friends. It all started when Dan and I decided to make one. We consulted Dave Kiff at Pacific tool and gauge, told him we wanted to shoot the 115 VLD and wanted to have less freebore than Weatherby's design. He made us a reamer to our specs and boy did it work!
The first two rifles used 28" Lilja SS #5 profile 3 groove barrels. Dan's rifle was a model 700 in a McMillan Lazzaroni sporter stock. Mine was a M77 tang safety Ruger with extended mag box in a McMillan hunter stock. Weight of either was 9 1/4 lbs. Using RL-25 and moly coated bullets we were able to get 3600 fps!
We liked the first two rifles so much we built two more lighter versions. This time we each got a #3 profile SS Lilja 3 groove. Dan went wild and had a model 700 skeletonized, fluted barrel cut to 24", added a McMillan edge stock, talley alum lightweight rings and a 3.5-10 x 40 VX 3. Total weight is 6.4 lbs. Mine was done with savings in mind. Left the action and barrel with full weight, barrel cut to 26" and used a Rem Ti stock weight 7.5 lbs.
I tried the 115 nosler BT and it wouldn't go very fast. I figure it was the bearing surface building pressure early. Those 115 VLDs have very limited bearing surface which helped with velocity gains.
Tim borrowed the reamer, used the same #3 lilja and put it into a rem 700.
Imagine....we had four rifles that all used the same bullet with the same load data and ALL shot into tiny ragged holes. Allen, Tim's friend saw what Tim had and bought my lighter 257.
Then we went hunting. It has been 4 yrs now and the animal count is incredible. 14 coues wt, 3 mule deer, and five elk! The deer shots range from 237 to 525 yds. The elk shots were from 50 yds to 400 yds. Many of these deer kills were DRTs, that VLD is amazing.
I also took the rifle out to shoot a few jackrabbits at longer distances. Oh boy what a varminter. It is not a rapid fire rig but for the occasional shot it is great.
Dan says it is the only rifle he wants to carry when big game hunting and he is the guy shooting all the elk!
I would suggest you build your 257 and use a reamer designed for your rifle and bullet choice. FYI all rigs have M1 turrets.
You think you are amazed after having a chance to see a 257 Roy, wait till you have taken several animals with it. It is an incredible chambering.