Slug barrel conundrum.

I'll check later this week when my new scope gets here to be sure, but if I recall correctly the .30 slug liner made an improvement on slugs and didn't change the pellet performance at long ranges. 

Did your pellet groups open up with the same tume? I know it is shooting them at slightly different velocities for nearly the same grain weight, and a decent amount slower with the additional 5 grain slugs.

Maybe a different tune is in order for the two different types of projectiles.
 
I did not see a difference in the pellet accuracy with my .25 Impact 700 slug barrel tuned and shooting the NSA 33.5gr HP slugs. It shot the JSB King MKll 33.9gr pellets just as well as the slugs without additional tuning. They both shot several sub MOA groups @ 100 yards when there was no wind at more than one velocity and more than one tune. My STX pellet barrel shot the pellets nearly as well with a different tune.



Five shots with pellets using the slug barrel lower on the target.



Three three shot groups one sighter with slugs. Check out the first three shot group on the bottom of the right hand target. ;^) 

Thought I was shooting off the bottom of the target so I tweaked the elevation shot the second group above it then adjusted

the scope again for the third group on the large bull. Other shots on the target were done while I was tuning.