I've never seen anyone try Retumbo in such a small case before, but it seems to be working well!
I started with 4831sc but was getting to much pressure and not the speed. I then tried H1000 and ended up with Retumbo. Each time you move to a slow powder your pressure drops. The trick is if you can get enough powder in the case to get the speed back. The long barrel helps with slower speeds. A lot of the bench rest guys in Australia are using Retumbo with the 180vld's Yes it is a little compressed load. Powder fills to just below the bottom of the neck. ES was 9 over 6 shots.