Recently had to replace the fill nipple on my Benjamin Maximus. Was shooting fine velocity stable and grouping wonderfully before but after the replacement Velocity average was spiking event other fill . Like first fill would average 790 for the first 20 shots then second fill would be 770 for 20 then like 780 on the third fill. And it kept going like that . Would fill with the samp pump to the same pressure same pellets and all. Well the other day I shot all the air out took the he gun apart for the most part , really just removed the air tube from the barrel ,took apart the trigger group , took the barrel off along with the reciver and top the hammer spring and hammer out the back.only thing I did was while some of the parts off on my shirt and threw it all back together. Seemed like all the deals I could see where fine. Well put it back together tighted every thing now with the same pellets and pump it's averaging around 795 every fill and it's grouping like it was when I first got it. Could re doing all the screws really make that much of a difference or could something else be going on ?