Need some input from more knowledgeable people on this.

I'm starting to beat my head against a wall on this. I bought a Savage 12 Benchrest used that had a low round count. I started w/ a .308 load similar to the load I used in a 10BA. The 10BA shot sub 1/2 MOA at 100 when testing loads and held .50 MOA out to 500 on a regular basis. I shot it many times at 1,000 at it did pretty well with this load.

I started out with same load for the 12 BR model and it did not respond. The rifle clearly liked a different load. So I played with powder to find a node and it also clearly liked a jump and I had to load them shorter.

So after I found a powder weight and velocity that worked well, I played with seating depth. The thing shoots killer at 100 yards < .50 MOA hole in hole type groups. However, when you take it to 500 or 1,000, compared to my other gun it shoots like crap. I've played with everything I can think about up and down and it seems like the gun just will not shoot. To remove the re-loading variable, loads done in the same equipment and process shoot great in my other rifle.

So my question is, what am I missing in this equation? It seems to like a lot of jump (around .035" has been best so far). I'm starting to think the barrel sucks and may need to re-barrel.

Here are the specifications:

Lapua brass, fired formed
CCI 200 or Fed 210 primers
43.5g Varget seems to be most accurate so far in Lapua, 43.7 in Win
175g SMK
Neck concentricity around .001"
Velocity is around 2750

I've chrono'd and had pretty good ES numbers. I'm at a loss with this gun!