Did quite a bit of tinkering with the tune today. The rifle really likes the AEA 21.9gr. They shoot well at about any velocity above 890fps but the real 'sweet spot' is 945fps.
Also fired the AEA 25.3gr from about 880fps to 930fps. The rifle does not like the 25.3gr at all. Pretty amazing how totally different the .25.3s and the .21.9s group from this rifle.
No further luck with the AVS ELR 26gr .2173" slugs. I won't shoot those again from this rifle.
Have some H&N 21gr .218" slugs ordered for next slug testing. At the very least..., if I can't find a slug tune that shoots with enough shot-to-shot precision I can always fall back to the 22gr pellets at a good high velocity.
My goal for this rifle is hunting rock chucks while on foot and shooting off a turkey seat using shooting sticks. Once I find the dens it's normally pretty easy to find a good place to sit, watch and wait that is within 75yds (or closer). Even if I have to shoot the .22gr pellets the rifle will have plenty of energy for humane kills! Accurate slugs would be preferable for better terminal performance but not mandatory for the way I will use this rifle.
At any rate, I have lots of time before Spring to work with the 250z and learn the rifle so no need to be impatient with a final tune and projectile.