HnS: I have only had one Lilja, a custom 270 Weatherby. It was FAST.
But I have seen the same things from Douglas tubes. I have one of those here that will give very good velocities from the 7 Rem Mag with pretty standard loads.
Just a WAG but these custom button barrels tend to run tight,are smooth,and get the velocities..at least that's what I've seen. IME when a rifle runs "slow" or "fast", the barrel and throating,interior dimensions,and rifling etc are the reasons.
