The ring will need to reseat before you'll get max compression.
Yup. When I recently replaced the barrel and piston on the 046, I could start it without the decomp without too much problem - not easy, but it would work. Now I risk cutting off a leg if I do it that way with a drop start after 20 or so tanks, the compression's gone mad. If I REALLY give it a go without the decomp, it will start, but that's got to be tough on the whole starter assembly. So run her easy so she sets and see what she reads. I was told to run it in smaller wood for 15-20 mins, let her set for 20-30 mins, and repeat for a couple of tanks, and let her warm up slowly.