Crown mk2 and light slugs

Ok friends, I’m looking for some advice.
I recently purchased an mk2 crown in .22 600mm with the hopes of using it for long range pesting. I would really like to experiment with slugs, and as everyone here knows, it’s a long process to go through. Having just got into the tuning, I kept the reg pressure where it was from the factory (120b), and just maxed out the hammer for that reg pressure. I ended up shooting 18grn jsb’s (I have a bunch of, so just using for test purposes), at 980fps with some pretty fantastic spreads between shots.
At this point, I’d like to tart testing slugs (around the 20g area), but like many others, finds and time are limited, so I’d like some recommendations first.
What has everyone had luck with in similar setups?
Thanks in advance for any advice.
 
My MKI slug setup:
Reg set at 133
FX Hybrid.22 grain slugs
878 FPS in my 380mm barrel

I use the above setup with 2 different barrels (both .22 cal)
The 380 mm barrel numbers are above. I also use that setup with my 600 mm barrel and it will shoot 4/10 of an inch group at 100 yards regularly. I have only shot 200 yards once but it held a 5 inch group consistently.

I know you have the MKII, but I think this info could at least be a starting point for you.
 
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My MK2 crown with .22 600mm barrel with superior heavy shooting 27.5 grain nsa at about 860fps is very good long range. It’s the gun and ammo combo I got my only MOA group at 300 yards.

If you want to shoot light slugs with superior liners then raise reg to 145 and shoot the 20 grain .216 or .2165 nsa at low to mid 900 fps range. 23 grain slugs will pact a bit more punch but the different isn’t huge and BC is about the same, the MK2 can sling those easily at mid 900fps range in factory form. For hunting/pesting 23 grain is the way to go.

Personally I would not go heavier than 23 grain unless you change to heavy liner.