RTI Prophet (MK1 or MK2) is, imho, one of the best platform to test slugs. They have more than enough power (with the bigger plenum), they are easy to tune, easy to service, easy to shoot, BUT barrels are the main issue when we are talking about slugs. The "old" LR .22 barrel is a 1:32 poly barrel especially designed to shoot JSB Mon. Red. over 950fps. Amazing choice for pellets, but horrible choice for slugs (that's fair, we have to choose between both). Now, they have introduced the RPB barrels, with a new TP and a lighter choke. They can be a good starting point, but keep in mind that BEFORE starting to test slug, you need to find the right diameter. Diameter is a game changer. Slugs are a lot more barrel/tuning fussy. Also, slugs have a lot more friction during the barrel trip (vs pellets), sometimes a light barrel polish will help you a lot. More friction means higher probability to have a damaged/scratched slug, and it will not fly well. I see a lot of people arguing about slugs and their effectiveness, without even trying to tune their guns or understand their barrel. This will not work. Slugs work exactly the same way that PB ammos work. They need right speed, right barrel and right harmonic node. Otherwise, they will not group. As simple as that.
I'have tried to use slugs in my Prophet MK1 .177 (and a lot of people say that this barrel is one of the best barrel to shoot .177 slugs). It shoots good, I can group ZAN 13gr under 0.5moa at 37-40y but, however, they performed worst than most of my pellets (hole in hole). So, what I did was ordered a slug specific barrel (LW Poly uncooked 24 inch). I will machine it and try it. If it doesn't work as I want, I will try another barrel with faster twist. And so on. Good luck!
