Chrony results before and after stuffed piston on 1377

[mcc1961]

Here is a before and after stuffed piston comparison of a 1377 shooting 7.0 grain RWS wadcutters.I shot my 1377 over the chrony because I was worried about consistency. I shot 5 times at 8 pumps . Then I shot at 10,15 and 20 pumps.Really satisfied with the results.I was using 7.0gr. RWS pellets.
8 Pumps
1.634fps
2.634.3fps
3.639.5fps
4.635fps
5.641.2fps
10 Pumps-676fps
15 Pumps-729.1fps
20 Pumps-751.1fps
AFTER STUFFED PISTON
8 Pumps
1.663.1fps
2.666.9fps
3.669.7fps
4.667.5fps
5.667.6fps
10 Pumps
716fps
15 Pumps
798.5fps
20 Pumps
846.9fps
Can't believe that it improved the string that much.

[mafatone]

I saw good results with the stuffed piston also. Then I did the "O" ring behind the pump cup trick for a little more power.

[nervoustrigger]

Nice job!  Your results are better than mine...getting about 10% more energy at 15 pumps, which is where mine begins to hold air.

I'm assuming a long barrel, maybe the full 24".  What else have you done to the internals?

How's it doing in the accuracy department?  Mine seems to prefer heavy pellets like Air Arms 10.3gr:

[mcc1961]

I have a 24" barrel, disco hammer  spring , an Alchemy boss transfer port and modified valve. I have had good accuracy at around 12yds at 7 pumps.Out at 20yds can't do very well, I have a 1701P trigger assembly ordered and hope it helps with the longer range accuracy. It shoots best with the Benji hollow points and Beeman hollow point coated pellets.