Slugs from the factory 1:17.7 twist LW barrel can be absolutely amazing. You're probably not going to get superb accuracy from the JSB or anything else like H&N, etc. The RBT Griffin.22-25's will blow the flat base away at long range. All of this depends on how far you want/can shoot also. JSB Knockouts & H&N are used by me to play with the settings & plink at close range. If I'm seriously going to try for great groups at 100-200 yards, it's Griffins for me.
I've got mine set up to send Griffin .2175" 28 grain RBT slugs at 1070fps. 32's are going 1040fps. That takes a 10 coil heavy spring & a heavier hammer. I've used a 115g brass to send 36grain NSA's at 900fps, 3Kpsi start, and they were very accurate. I found I could use the lighter hammer, have way less drag and more consistent shot spread with a 95 gram hammer, 10 coil spring, .178" top hat about 0.012" feeler gauge between spin lock and top & use lower fill pressure, start 2500psi. Power wheel bottomed out & only use for fine tuning
Shooting tethered with a step down in-line reg from a rested position it can print dime sized groups all day long at 100 yards with good slugs. I'm just a target/plinker guy; but I chase the accuracy for fun, so Griffins are worth that to me.
They're the best, meticulously swaged and checked by hand slugs I have personally tried. Many others are probably just as good. Varmint Knockers are still done by hand I believe also.
Slugs aren't really worth getting into IMHO unless the shooter has a long range to stretch them out, or needs high penetration for pest skulls. Otherwise, .22 pellets at 880-940 are definitely going to outperform slugs & remain my main choice for general 75 yard or less airgun shooting.
