Benjamin Discovery at 40 yards

I'm guessing yours is .22 cal? That didn't look to bad for a disco but here's some things you could try. With mine I thought that the JSB 18.1 grn pellets shot the best for a couple years then they came out with the Crosman piranhas and they shot way better so be sure and look at trying different types of pellets. Another thing you could do is clean your barrel with a piece of weed eater string melted on one end and sharpened on the other so then it can pierce a patch then hold it from falling off the string with the melted end while its being pulled through the barrel.
 
 Yes .22, ive tried around 10 different pellets including all of crossman's offerings. The JSB 18s shot the best followed closely by polymags. Barrel was cleaned around 300 shots ago and the groups have been the same since. The top right of that target was shot with H&N hunter extremes and they were grouping horribly. around 2 to 3 inches at the same range.