I have an Accumark, which is the same thing, I think, except for coloring—bot have a full-length bedding plate and are free floating. I love mine. My favorite rifle.
Did you get yours made custom? Weatherby does not appear to list 340 as an option on their website for the Terramark. Are you going to hunt with it?
I don’t handload, but the Corbon-loaded 225gr TTSX rounds leave my muzzle at 3,160 fps. At sea level, that bullet is still going 2,250 fps at 500 yds. At 10,000 ft (where I plan to use it next on elk and black bear) that bullet is still going over 2,500 fps at 500 yds. It retains more energy at 500 yds than a 30-06 does at the muzzle. Pretty big hammer.
My last five 3-shot groups are these at 100 yds. The larger one was when I let the barrel get a little too hot.
As to recoil, just ignore it. Like elkaddict, I have no brake, and don’t need one. I wear a Cabaela’s version of the Past-style shoulder pad when sighting in at the bench. It makes a BIG difference. I can’t over emphasize how much difference wearing a pad on my shoulder makes. I never get bruised no matter how long I shoot. I know the rifle is going to push me back, but not hurt. So, it allows me to ignore the recoil. My father is recoil sensitive with rifles. When he was getting ready to go to Alaska with me, he was considering taking my Rem 700 BDL 300 Win Mag, but thought the recoil would be far above what he could tolerate. I sent it to him with some Federal 180gr TSX loads to try---along with the recoil pad. He was shocked at how little the recoil bothered him wearing that pad. He had shot it when he was 22 years younger, and didn’t like it at all, but it didn’t bother him at all with the pad on his shoulder, and he was getting 1/2" groups with it.
When I first bought the 340 Accumark nine years ago, because of all the hysteria I read about its recoil, I bought a bunch of 200gr and 210gr cartridges, hoping I could handle those, and that they would not rip my shoulder completely off of my torso. I fired a couple and immediately realized that it was no big deal. I still have those boxes of lighter ammo with just a few rounds gone. I immediately went up to the 250gr NP loads. Still no big deal. When I squeeze the trigger, it’s going to push me back, but not bruise me. No big deal.