I used the knockouts in my BSA R10 TH and they went through fine.
Though being a sub 12ft/lb they are slow and the drop is substantial. That said they do carry a lot of energy down range.
I'd certainly be using slugs in a FAC gun.

What I have been doing is buying sample packs of 50 off of ebay.
So far I think the standard JSB exact 15.89 are still best out of my barrel, but its fun to experiment