Just a note on my experience with Remington 700 bolt guns. The rear of the bolt where the sear is locate does not fit snug, and has a lot of vertical play, which allows the sear to slip off the trigger and fire. Do as Bergara says. Theirs may do the same. I don't have one to test.
I have a model 94 Win. in 30-30 built in the 1970s. The lever is pinned in and was never properly tempered (really soft metal). It peens the part of the lever that retards the shells in the magazine from coming out all at once. I have to peen it back down at times to make it work properly. The 1970s were a real mess for quality assurance. Ford cars were a piece of junk back then and so were Winchester rifles. The rifle shoots good though. The older and newer rifles all seem to have much better quality control.
I'm not a competition shooter, but I found the same inconsistency with Hornady ELD-X bullets. They can differ as much as .007. I hunt with them but don't need to shoot beyond 6 or 700 yards, so something under 1" grouping is okay. Target and competing are a different matter; consistent, consistent, consistent, to con a phrase from the realty profession!
Different guns like different bullets. I've had mixed luck with Barnes LRx. The trouble is they are very expensive, to costly to experiment with. I found a few loads that work for what I need them for - I load them if big mean bears are in the area I'm hunting, otherwise I prefer Hornady SSTs and Nosler Accubonds or Partitions. You might try the Hornady Outfitter loads. They are loaded with their GMX bullet. They shoot good and I've had good luck with them.
I have used 260 Remington case. The only problems were it was really easy to dent the shoulder area, and they need to be inside neck turned to remove the donuts where the shoulder of the 260 becomes part of the neck of the 6.5CM. 243 cases will probably have the same problems. Should anneal the cases when your done.
It depends on how much you are willing to spend and what your real need is. The LabRadar seems like a great purchase if you do a lot of load testing, but very expensive. The Magneto Speed is great for seeing your velocity rain or shine, but it attaches to your barrel, so will change your point of impacted. I use the Magneto Speed Sportsman most of the time for quick checks on velocity, but need to remove it to check groups. It works rain or shine, so don't worry about the weather and carry it in the truck most of the time.
Hunting in very cold weather, stick to large rifle primers. If you want to try your hand at the best accuracy in your rifle you can always go to small rifle primed cases later. It's always fun to get the best accuracy out of your rifle. Here in Montana it gets very cold during hunting season. I stick with LR primers. Welcome and good hunting.
If you are not worried about saving hides, then try the Hornady 123 gr. SST. I've used them to 565 yd on coyotes and they cut the wind better than lighter bullets. It also makes a great antelope bullet.
If your coming off a magnum action, why don't you just neck up a 243 WSSM or 25 WSSM case? The case head should work with the existing magnum bolt face. Of course the case is slightly wider than a 7Mag.
I'll try and upload a picture of the coyote I shot at a measured 565 yd yesterday. I was using 123 HNDY SST. He popped up out of the river bottom and stood broadside. I pulled the first shot a little left when a puff of wind caught me, the second shot went between his legs and he moved about twenty yards closer. The third shot hit in the front of the chest as he was facing straight on. I thought he was on my side of the river but it took a bend and he ended up on the other side, so the picture is of him laying on the far shore. I forgot to add that the first bullet hit the yote just in front of the right hip. The third shot was the one that put him down.
Sportacus has a reasonable alternative. If you sight .66 high at 50 yards, you should be dead on at 200 yd. I used an average velocity of 2900 fps and a scope mounted at center 1.5" high. Most lead free projectiles will be very close to this sight-in. Where you going to hunt in California?