Tuning Daisy 717 rebuild help

[marflow 777]

so the piston head on the 7-7 pistols need to be surfaced if you really got down to best results

there is a case strip down the middle of the piston
now this was fixed on the post with a lathe but a file a V-Block would work if you wanted to also look how poorly the casting is
you could reface it or something else but the gain will be what
i have 6, 7-7 and have never done it

 

[Steveoo]

You beat me to it, but if you perform the skim right up the lip of the O ring groove, you will gain 15 fps...
You only need the slightest witness of wall on the front of the O ring as it will not pull off owing to the majority of the slot keeping it in place, while all the main pressure is going to the back of the groove which is untouched...
After performing this mod, simply ensure the face seats right up to the. Bulkhead.

 

[beerthief]

I use a long bamboo skewer to clear a barrel . also try a tissue over the end of the barrel when you pump that would indicate the valve is dirty and not closing .

 

[Hummer57]

The 717 can easily shoot as powerfully as the P17 but it requires the piston head to be set up to dead head against the bulkhead which contains the valve.
This is easily achieved but very few know how to do this correctly and are happily shooting guns where the piston head has clearance ahead of the piston seal face and the bulkhead....which equals wasted dead space. Max pressure achieved with minimum, or zero gap.

Essentially, the pump head is adjustable. It takes a bit of fiddling but not difficult.
Open the lever and have the open cocking slot facing you.
Loosen the locking nut and wind the piston head up until it just nudges the bulkhead.
Now lock the nut..
Lubricate with SIlicone oil ....there are better lubes but not better sealing ones..
This will give you 385-390 fps with 8 grain pellets provided seals are in good order...
Get to this point first then I'll show you how to gain a further 15 fps

 

[Hummer57]

I may get it out and give it another go!

 

[marflow 777]

so is the pump head work worth it, i don't know but be aware there are no more pump heads parts for the 7-7 are slowly disappearing
rear sight are all but gone
but they are a simple pistol to work on and if you what some wood grip get ahold of Vernon Austin gorgeous

 

[Steveoo]

Obviously the careful adjustment of the stock piston head to get it to a minimum clearance at closure will see maximum from the stock gun.....approx 385 fps ish...instead of often quoted 340 to 360 fps...so this part worth doing and zero risk..
Polishing the head down ahead of the piston ring to gain another 15 or so may not be worth it for many...