I got the modest gains shown in column 2 and was pretty happy.
But then remembered one of the posts I had studied, mentioned the
o-ring... Thought about the space between the piston cup holder, and
the piston cup, created by the shim/washer, which was needed to adjust the
piston length, because of the valve being slighly ~.040" shorter.
(the hip bone is connected.....)
The washer shim is still in it + the o-ring.
Sooo, I put the puny looking o-ring between the cup and piston to take up
that area. Picture shown in this linked thread. (easier to post pics there)
WHA-LA ! (magic) that small puny o-ring must have let everything else seat
completely, granting me my wish of "mo-powa" at 3-5 Pumps, and even more power
at more pumps. Amazing how much that space was giving away, even after stiffening
the piston with the steel rods.
If I do this to another 1377, Or someone else ?, I would like to try the sequence
of mods in a different order....
1. Get good reliable Chrony numbers for baseline.
2. Change out valve spring for a lighter one... Chrony change.
3. File/mill valve face to mate with pump cup, shim adjust piston length loss....Chrony change.
4. Add o-ring to cup/piston....Chrony change.
5. Put rod/shims in piston to simulate solid piston...Chrony change.
Based on my numbers, If you arent trying to get to 700fps on 10-?? pumps,
these relatively easy and cheap mods will improve the 1377 to be an even better Backyard plinker.
BTW...after about 100 shots, re-chrony'd today at 3 pumps. 399-398-401-404-402..