FX Impact 22 Cal ...what weight Projectile do you need to go to slug/heavy liner

If you don’t care to shoot pellets at 900 FPS or want to only shoot slugs then go heavy regardless of slug weight. My impact in .25 will not be shooting pellets at all so it has a heavy and shoot all slugs I put in it well. In .22 I’m tempted to go with heavy but I do occasionally shoot pellets so sticking with superior for now, might go heavy in the 600mm barrel and stay with superior in 500mm. I won’t go heavier than 23 grain slugs in my .22 superior though. 
 
Superior standard up to 30gr h&n. Heavy for slugs and standard for pellets is more like marketing stuff, you have to try every slug with each barrel and you will see what I mean. Some light weight slugs work better with heavy than standard and the opposite is true here. 30gr h&n works like dream with superior standard, half moa to three quarters all day.
 
I have the superior heavy in my .22, and LOVE it. The lightest slug I shoot is the 24.8 grain NSA, and it does just as well as the 31.2 grain NSA. It also shoots 36 grain Griffin slugs very well. It is about 1/2 MOA accurate with those at 100 in what little testing I've done. I generally shoot the NSA 31.2 grain in mine, and it does prefer .218 in my case. I don't shoot pellets at all, so the heavy only makes sense for me. If you're one of the folks that follows the twist calculators religiously, then the heavy is for you as well.