Hey, I tried a dozen different slugs out of my Barra 250z, only 2 shoot lights out. Awesome! I only needed one. If you want a .177 that shoots everything well then sell yours and say it shoots 1/2" with these 2, and crap with everything else. That's just airguns. Better yet, provide the list of the other 22 that you tried, to save a new buyer the wasted time. I think that I wouldn't have tried so many different brands with a .177. I would have only tried brands that had multiple different head sizes, or known success, and stuck to a weight that I knew the barrel twist and energy I was going for, could be stabilized, and was accurate, in other peoples same gun. Since it's a pcp I only would have used between 10 and 13.5gr pellets for sure, JSB and all the H&N because they have a lot of different head sizes. Between those two brands, If I couldn't find one that shot well in .177, I'd sell it too. There are plenty of people that are looking for a winter project gun right about now. At the price you seem to be willing to take for it, you'll sell it fast.
What I'd really suggest is that you experiment with it. That would be more valuable than the money you'd get. If your Gen 1 doesn't have a regulator, get one, they're cheap from Barra, and up the power and try again. I found that I actually like getting the guns to shoot well more than having guns that shoot well. It's something interesting to do. Good luck!