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Groups out of a carbon barrel

I have a Proof Carbon barrel on a 28 Nosler. I've tried different powders, bullets, seating depths, primers, cases, about everything. With a good load it prints the first two touching and the third opens up to about an inch. This is very consistent in my rifle. Bullets are all HBN coated. As the barrel heats in this hot Magnum poi shifts around. Ok to hunt with for long range, its just a 2 shot gun. It won't last long and it will be my last carbon barrel. So I'm not surprised about your troubles.
CFW barrels have more mysteries attached, in general.
There's one manufacturer I'm going to try that doesn't seem to have drama with theirs. 🤞

It'll be a 500yd hunting gun so I'm more confident it will work…
 
CFW barrels have more mysteries attached, in general.
There's one manufacturer I'm going to try that doesn't seem to have drama with theirs. 🤞

It'll be a 500yd hunting gun so I'm more confident it will work…
Here is my unscientific (WAG) on what's going on with them. They are supposed to dissipate heat. This is true on the surface of the barrel. I can shoot the 28 three times, wait a couple of minutes and the outside of the barrel is cool. but a barrel cooler on it and the air coming out will nearly burn your hand. I think the carbon insulates the SS barrel and actually holds heat inside. While the OP's barrel is cool to the touch, it is still smoking hot inside. Any stress between the carbon and SS as the SS heats up could cause all the issues everyone has. But this is just a guess.
 
When things "don't shoot" it's time to take off the scope, take off the stock and be very purposeful about the re-assembly.

Lay the bbl'd action into the stock and make sure there's no "teeter-totter" effect off the recoil lug, mag box, or bedding that's not level. Same for the bottom metal, it needs to lay in place, flat, no teeter-totter, no binding. Is there contact w/the barrel in the bbl channel, or the stock w/the trigger housing/safety lever, bolt release?

Action screws and scope mount screws that are SS get a coat of sharpie on the face, torqued down, removed, look at the face of the screw and make sure it didn't make contact with the action, a bolt-lug, or the bbl tenon on the front scope-bases screw. Blued screws I remove the bluing off the face with a wire wheel or a small file and do the sharpie trick. Also make sure that your action-screws aren't making contact anywhere in the hole. Action screws should only make contact w/the action via the threads, nothing else. Action screws should make no direct contact with the stock anywhere, just the head portion with the bottom metal.

The scope or a lapping bar should lay in the rings level and straight. Look @ the scope tube/lapping bar in the rings just like you'd look @ a bbl in a stock's bbl channel. The gaps should be even and there should be no teeter-totter front to rear and full or nearly full contact. Rings on bases w/slope built in still need to allow the scope to sit "on-plane" and there needs to be no torque on the tube.

If the above doesn't get things moving in the right direction, pull the ring caps and swap on a "known" accurate scope.

If the new scope doesn't work, check, or have checked the crown.

If all of the above checks out, THEN I start to think "new bbl".

In my mind, I pretty much always assume repeatable "flyers" are a mechanical/assembly issue until I tear-down, reassemble and prove they're not. Then I think scope, then barrel.

A couple of Allen wrenches, a T-15, and a sharpie can cure a whole bunch of headaches and save a crap-load of time not waiting for a new bbl or your turn @ the smith's equipment.
 
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