Yeah I agree don't clean the bore every 10 or so shots.The bore was probably lapped to a mirror finishand you just might wear the barrel out sooner by using Butchs Bore shine that often.I personally don't know what could be wrong.I do know there is a trade off between lengths of barrels.Longer barrels will give more velocity but the also vibrate and can cause accuracy problems when compared to a shored stiffer barrel.But I know the accuracy problem can be fixed with the proper powder bullet combo. It's gonna be a crap shoot though.
Especially when you don't handload.Personally I be happy with the 1.5 inch group you have and go with the factory ammo. Accuracy may improve once the barrel gets more shots through it.Oh one more question.Is this rifle used for hunting or competition or both. Cause 1.5 inches isn't that bad for factory ammo in a custom gun if it's solely used for hunting.