He would not tell me as he likes Dan very much but had a repeated problem with a few bbls in various calibers where the problem was solved when a Hart tube was installed. Dan builds phenomenal barrels but no one builds them 100% of the time.
The one downfall I've experienced with the Lilja tube is the steel sometimes does not cut like other steels like from crucible.
I've had rifles built with the Lilja bbl and the smith did not do a chamber cast once complete and After shipping back to me, I go to the range only to find some cases won't extract without great effort. There were small chunks taken from the steel while chambering that left the brass filling the void with fired case. Allegedly, this was with a relatively new reamer too.
So, my lesson was that (as related to me by the builder) with 2 barrels, Lilja and Lothar Walther, the chambering process should take a little longer or that the steel cuts differently and that Carpenter steel can be more brittle.
Until the day comes where I start building rifles (which is never), I have to rely on the experiences of the builders I choose to help me make informed decisions.
Plus, in my experience and opinion, Hart barrels are the top button rifled barrel style available.