My rimx wears an 18" Bartlein chambered by Curtis Custom Weapons in Clarence, MO. I have only ever run sk standard and sk semi-auto through it. I have run 3 lots of sk standard and they have been from one hole to .3 in. for 5 shots at 50 yards. Back when I bought the ammo it was $500/case so the accuracy is damn good for the money.
The semi-auto does not shoot as good as the standard plus, but it is still good enough to consistently hit 2 moa targets from barricades during practice.
The only thing I would do differently is use a longer barrel to get better balance for positional shooting. In an ARC XYLO it is somewhat rear heavy.