I have the 25 Caliber Benjamin Nitro piston gun it shoot great but recently accuracy went south First thought was scope slipped again as this does happen . Ended up bore was all carboned up .
So how often do you clean your air gun bores?
I do need to explain a bit about the issue As soon as I got the gun I bought three pellet weights and also started cutting dies to swage pellets . I found my home swaged 20 grain pellets formed from cast #4 buckshot shot best and had much better weight consistency then any of the three factory brands. ON Here I learned to use the silicone lube for the piston as lube but before that I had tried another lube, I ended up being happiest with lanolin I just spray finished pellets with the case lube mix of alcohol and lanolin shake them and let them dry.
My first batch was lubed with a heavy lube they shoot well but these are the ones that really messed the bore up I should have guessed by the smoke produced when shooting them! The lube was a pond of paraffin slowly heated and mixed with a 15 oz. can of STP motor oil additive and a couple blue crayons for Identification.
By the way if wondering the combustion of this lube adds nothing to the pellet velocity which is a bit low at about 800 f/s for a 20 grain pellet .
Other results I noted ( did not note make of them, tin pellet is from my dies made with plumbing solder)
27.7 grain pellet with hollow base 520 f/s very poor accuracy some missed target. (Home swaged Solid bottom pellets shoot best)
12 grain pellet of tin 900 f/s 4" group shoot high. (This one really made a crack on firing first thought was is was super sonic that was not correct the crack was the piston slamming harder from light weight I believe!
Factory 27.5 grain pellet 630 f/s 4" group if pushed in chamber further with pen 5" group and a loss of 100 f/s!
Factory 34 grain pellets do 580 f/s and about the same accuracy as other pellet they do seem to go further into wood.
Seems I have not written down any data for factory 38 grain pellets?