I've used the GB slugs on plenty of pigs in my old Adler and in the better Dickinson straight pull.
They definitely do the job and seem very similar to the RC4's, blackhawk also make a version that's so similar the the GB's I wouldn't be supprised if they came from the same factory.
Unfortunately the two pig properties I visit fell on hard times, one opened up to pay to play and got shot bare and the other went 3 years without rain and had to destock and even the roo's left it.
Once they pick up again I will be back out chasing them again.

But slugs and pigs just seem to go together, I'm even a fan of SSG buckshot for the up close stuff.
It's great to be able to roll some bunnies and foxes with the same gun you chase the pork with too.

I've gone the poor man's double before and it did a great job, I even scoped it for a while. Thats when I switched to the Adler and then the Dickinsons but I just had to switch back to the double, for some reason I just find doubles to be much better guns and feel better in my hand.