I built up a little 177 slugger from mostly Benjamin and Cothran parts, Magnum valve. Not had a chance to get it to the range yet, just too windy, but in my garage range of about 30 feet, it will make 42lbft with the NSA 20.5's. The groups tighten up a bit with NSA 15's or JSB monsters. All groups are clovers but the 15 grainers just shoot a bit tighter. With a light pellet it will push 1300fps. And this is just with a cheap 24" Crosman barrel. May be time to put a "good" barrel on it and see what it can do. It could certainly use a faster twist for the heavier slugs. And a heavier barrel not requiring barrel bands could "float". Hmmmmmmm
Chris