Tuning Daystate Huntsman Revere - tuning?

I have a .22 Revere with silencer, and it is totally yard friendly. I've never had mine apart, but I've reviewed the diagrams and seen some videos. Basically, the rifle is not designed to be adjustable. I expect that a 20 fpe tune might require a different hammer spring. The same rifle in .177 and a silencer should be very quiet. 
 
I have a Huntsman Classic .22 and it is loud, it shoot around 750 FPS 18.13 I put a moderator on it and I can't get a good group 


Couple of thoughts. It should be shooting faster, maybe 830 with the 18. If the accuracy goes south with the moderator, then you might have an alignment problem. Given the low velocity and the noise, I wonder if you have a blown breech seal. Have you inspected it?