I think the biggest problem with trying to shoot heavier slugs in .177 cal is that the twist rates of .177 barrels are just too slow.... Cedric (tofazfou) and others (including me) have been using the 9" twist TJ's barrel in .172 cal and NOE 24-26 gr. slugs and getting stellar results.... My regulated PCP, at 2800 psi, gets 1050 fps with the 24.7 gr. HPs at 1.0 FPE/CI efficiency, and no sign of instability in the slugs.... With most .177 barrels being 12" twist or slower, you simply won't be able to run heavy enough slugs to really see the advantage available....Bob
Stock .177 Buccaneer JSB K.O. 13.4g @~20fpe... pretty much moa at 50 yards... handles light winds very well...
Following. I've been watching the South African guys hitting targets at 3-400 yds in their video's.
It's a 28" barrel.... 14mm TJ's sleeved up to 20mm with CF tubing.... Bob
My .172 cal is but one of four calibers (.172, .224, .243 and .257) I can interchange on two PCPs I built from scratch, one regulated and one not (good for up to 4500 psi).... Here is a photo of the regulated one....The unregulated one has a full length reservoir with no bottle underneath.... Here is a photo of the .172 cal slugs I tried, four weights of Varmint Knockers and the cast NOE 24.7 gr., which was the best.... The longest VN was unstable in the 9" twist, and the next longest one was marginal....Here is a photo of the NOE HP in a block of soap at 60 FPE (at 2800 psi)....Lots of fun.... Bob