dumb me---should have done this before now--

I got the crazy idea tonight to put a small bit of baking flour on the crack between the breech and the pump tube on my 1377 around the valve exhaust area to see if I had a air leak.
And yep, with 10 pumps in it I fired a couple of shots and it leaked out the right side and worse out the left side.
So I took the breech off and removed the factory rubber washer and transfer sleeve then broke out the ole dial calipers.
I measured both the breech port and the valve exhaust area for a total length of my
poly tube.
I cut the tube to length and rounded the top side to match the barrel and installed it.
Took maybe 30 minutes from start to finish.
Now I ran 10 shots over the ole chrony before the mod and came up with an average of 502 fps.
Well after the mod I did another 10 shot string and was blown away when I averaged 558 fps!!
I would never have believed there was "that" much air escaping with every shot.
I wish now I would have done this mod alot sooner.
Just goes to show you that even the smallest mods shouldn't be overlooked when souping up these wonderful airguns.
Thanks
Ray