That particular X caliber bbl shoots like a house a fire, no kidding. I have never used Norma 6 XC brass, so I can not compare.
When I first got the 6XC caliber, I was wanting to replace the 243 for a calling rifle and deer rifle. Some cases have inherent accuracy, and I did not want a hunting rifle that I had to buy high dollar brass for.
So, I formed some cases from Chinese Military 308 brass that had been fired in a machine gun, the groups were in the very low 2's with the crappiest brass I could think of. Then I formed some out of PMC once fired brass that I bought off the net cheap. Same thing, but the primer pockets did not get loose in the PMC brass. Next, I have found lot of Lake City 308 unfired, and I expect this brass to be tougher than Lapua brass.
So, I set at my bench, form brass, then neck turn while I am watching Fox news in bad weather.
At 1000 rounds, I will measure leade growth and see if that long neck with .130 freebore has lowered pressures enough or changed the turbulence point to where I may get longer barrel life...probably wishful thinking. Gives me something to play with.
With a .400 long neck, you also have the option to leave the throat at a normal .105 freebore, which would push the bullet back in the neck and perhaps give you longer barrel life this way as the neck would eat up (.105-.075 regular neck length). You would have a lot of bullet contact in the neck...this may mean that you need to drop down to .001 grip on the bullet and perhaps lower the powder charge to change the "tune" as pressures will go up from the extra neck/bullet contact.
We have heard a lot about Turbulence point in various cases, especially when it comes to the barrel life of a 6 Dasher vs a 6 BR, I want to see if there is anything to this(short neck vs long neck).