Have been goofing around with this indoor target gun for awhile, posting occasionally on the above old thread, but thought I'd bring it back up to the top.
This .177 pistol: (can see the simple power adjuster at the rear end cap):
This Pro Top valve: If you don't know the product, its a replacement valve head that self pierces the 12gr. Comes with good instructions, so call it a level 2 installation, No valve stem needed, so a Delrin valve was made. A STIFFER valve stem return spring used to speed up the valve cycle.
This reduced transfer port. Sleeved it with a length of empty ink pen cartridge:
This lighter striker (nothing fancy, just ground/filed two big flats):
Temperature testing. This is an indoor gun 95% of the time, so I want it to run right at about room temperature. All test using 8,3gr RWS Super Domes.
So starting at 78F (letting the gun adjust to the temperature) Shot as FAST AS I COULD, while still getting the pellets over the chronograph screen. Idea here is that I want to know how quickly the gun cools/changes velocity.
TEST #1: With zero pre-tension:
Can see a definite velocity rise as the gun cools off.
TEST #2: 1/3 spring tension:
Again, a gain in velocity as the temperature decreases.
TEST #3: 2/3 tension:
Really kind of stable for those 10 rapid shots. Evidently at this temperature, it is pretty well in balance.
Test #4: 3/3 (full) tension:
Decreasing velocity as the gun cools.
So, set it at 2/3 tension. Having fired 40 rounds already, and gotten velocity readings for different settings, plinked for another 30 rounds. Knocking around a cheap set of spinners set out at 20 yards.
Shots from #70 on ward:
So I saved some gas on the 10 round tests at zero and 1/3 tension settings, and wasted some gas in the 10 round test of 3/3, but think I can call it 85 decently consistent shots at about 3 foot pounds.
THINGS LEFT TO TRY:
An HDD. Not real sutre what that would do at this stage of tuning (maybe bring me all the way back to the beginning to start over).
Stronger valve return spring.
Even lighter striker (there is still weight that can be removed).
Wider valve stem in order to decrease gas flow to the transfer port.
Think I'll just lock down the settings as they are. IF I decide to take it out into the heat, will crank it up to full tension (and gain about 50fps but cut shot count by about 1/3).