There's a lot here to respond to but I first and foremost, you probably don't want to increase the valve volume for .177 and probably not even for .22 unless you will also be fitting an 18" or 24" barrel. That is, unless you like pumping and pumping and pumping and watching your efforts spew from the barrel long after the pellet has left. The name of the game for improving the energy per pump is to reduce headspace. The gap between the valve and the pump cup. There is a DIY in my sig for improving the stock parts. To do more, you would need to move to a flat top piston and valve.
You need more beer
OK problem #2 the peep sight will not go down low enough to raise the Pellet where it needs to be on target at 20 even 15 yards. Even 10 yards it hitting low. Looks like I need to dremal the sight adjustment slot longer ....
...order yourself a pump tube from a Powermaster 66 as well as the pump linkage. You'll have to drill a hole in the bottom of the tube for the front grip screw in the valve, but you will gain about 1/2" in pump stroke I believe, and the linkage is a little longer putting the pump still back by the trigger guard. The 66 uses the same valve as a 13XX and the same piston just a longer pump stroke and linkage. I have yet to do this on a 13XX... You can also use a 2100 tube and piston and such but there's more mod work involved...
Quote from: Rogergendron1 on June 27, 2016, 08:42:04 PMOK problem #2 the peep sight will not go down low enough to raise the Pellet where it needs to be on target at 20 even 15 yards. Even 10 yards it hitting low. Looks like I need to dremal the sight adjustment slot longer .... Lowering the rear sight lowers the impact, and vice versa. Those peep sights work fine for me.