In an 18" barrel the 6cm still gets surprisingly good velocity. I just tested 105hyb and 112mb in my 18in yesterday. Was able to get up to 3000fps with both, H4350 w/ 105s and rl26 with 112s. No bolt lift or ejector marks either. Case web diameters on lapua brass tell me its pretty dang warm, as they're only .0006 under chamber diameter. Going to run the 2900 node with 112s as it likely has a lower velocity threshold for expansion and has same wind holds as the 105 at 3k. It's a lot lower pressure as well. I've shot a lot of 6gt, several barrels worth. It does just fine with 24-28" barrels, but an 18" is gonna take a lot of it's steam, beings it holds 8gr less than the creed. The 6cm at pressure from a 26" is 200fps faster than the 6gt w/ H4350 when I compared a few last year. In 18" I think it'll still be 150fps faster just do to the efficiency of the smaller case. 6gt id go no less than 20" as I think you could still run the mid 2800 velocity window without being too close to pressure. I have a 21" gt being cut for my Tikka now.