I have a 20BR, built on a Sako 75 action by Neil McKillop.
It is very accurate with 39gr SBK but what it really needs is a high BC bullet in the 50gr area but nobody does them anymore. You will also not get the velocity that is banded about on the internet, I cannot get above 3800fps (24" barrel) with mine, I can get nearly 3700 out of my 20Tac which is much easier to load, feed, buy etc etc
Good 6BR brass is easy to find, forming the brass is a pain in the arse and must be done in several steps then it has to be neck turned as well, I did 200 and I am planing for this to last the barrel out. I am not expecting the barrel to last that long either
In the Sako 75 you need a special PPC mag which is very hard to come by and it still doesn't feed great, it feeds but you need to be firm with it. It only holds 4 rounds as well. A T3 or a custom action would be a better starting point IMO
The 20BR was an itch I wanted to sctrach but when this barrel is done it is going to be replaced with a fast 22 or 6mm where the bullet selection is much better