Tuning 600 mm 177 fx barrels

I have a STX superior 600 mm .177 in my FX M3. I've got Air Arms, Fx and JSB 10.34 to shoot really well in them. I know they are made in the same place but the FX and Air Arms seem to shoot a bit better. That is the case from 12-23 FPE. 8.4 JSB and FX shoot well too but not as good as the 10.34. I just got some JSB Monster Redesigns and they shoot well (I agree with 2 Much air). I've tried Howler and JSB knockouts. So far have not found great settings for either, but the JSB knockouts (13 grain) seem to be the best slug so far. Good luck.

How do you guys find the lead fouling on the FX .177 barrels. Mine needs frequent cleaning. Sometimes as often as every 150 shots.