Tuning PP750 low tune

[rash_powder]

Hello all, 

a coupes months ago I got my PP750 and love it! But being I only use it for paper at 5m, I would like to tune it down to 350-400fps, and maybe even get a few extra shots out of it. I’m thinking most of this will be accomplished by lowering the regulator set point, correct?


I have seen a process for a max power tune where the hammer spring is maxed out, adjust regulator, and then back the hammer spring off to the speed you want. Is this the process I should follow for a low power tune? Or should I minimize hammer, adjust reg, adjust hammer?

I may polish and debut all the washers in the reg too while doing this. Are there any pointers or a general walk through of this some where?



thanks!

 

[Fatmike]

What are you shooting now fps? With the canada restricted valve you should be close already.

 

[rash_powder]

I would love to actually know, but my chronograph is giving me troubles in the garage. I haven’t been able to sort the lighting out for it, so may just have to set it up in the driveway. I don’t care for that route though as I live in town and am concerned the neighbors may get crunchy. I doubt that would happen but you never know. 


if nothing else I would like to get a few more shots per fill. I’ve an o-ring order on the way and hoping a rebuild will slow to stop it’s slow leak too.

 

[bigHUN]

Replace the hammer spring to a softer-shorter, that will easy the cocking lever as well. I got some softer springs from McMaster for $5 a 6 pack ordered 3 sizes and play with them

 

[ctshooter]

Also watch you don't go too low on reg pressure. It might have to be a combo of reg and HS. As I recall my PP750 liked to degass itself when the pressure got down to ~80 bar.

 

[boscoebrea]

I have the Canadian model in .177,low power...get about 24 good shoots ;have not touched a thing,,,accept to lighten the trigger.

I think the smaller valve may help you.....that said I am not sure what the shoot count is on the USA model.....anywhere near my shoot count would then Not much help.....

 

[bambuino]

I have the Canadian model in .177,low power...get about 24 good shoots ;have not touched a thing,,,accept to lighten the trigger.

I think the smaller valve may help you.....that said I am not sure what the shoot count is on the USA model.....anywhere near my shoot count would then Not much help.....

For my PP750 in .22 I get about 28 shots, shooting 235 bar down to 110 bar. I seem to get the best accuracy on the first 21 shots, down to 130 bar. This was at the factory 12 ft/lb tune.

if nothing else I would like to get a few more shots per fill. I’ve an o-ring order on the way and hoping a rebuild will slow to stop it’s slow leak too.

Curious if that is a factory SPA o-ring kit specific to the PP750, or did you order generic selection kit? Would like to get a spare set. Blew out the gauge o-ring degassing (11.0 x 1.5mm), have a spare, but be nice to have another full o-ring rebuild kit in the bag.

 

[boscoebrea]

The difference in shoot count is because I did not fill it as much as you did.

If you already have a 12# I would think you already have the small valve...

When Wes first sold the PP 750 you had a choice of low or high power...he sent the first 750 "sold to USA buyers"to Veradium Air to change the valve to higher power plus "tune" the pistol....people were very happy to pay for the cost of that service.

If you already have the low power valve you would need to tune it as others are saying.

I will say this about small tube PCP that have good power,None of mine get me over 28 shots of good power....all hover around 2600=2800 psi.

The SS750 can take more air like I think 3200psi....should give more shots ....

I am using these measurements of the top of my head and would welcome to be corrected.

Went I went to Wes site a while back I think I saw extra orings listed.....I believe my new SS750 came with extra orings....I have put that pistol up for the winter ....I will check it out later....

 

[rash_powder]

Bambuino- I got the exploded print/parts list and ordered all the o-rings needed individual. No kit that I’m aware of.

ctshooter- I did notice while degassing that at some point the pistol did just totally exhaust itself. Has me a bit concerned about refilling it now.


I ran into a bit of a snag trying to grind my set point and where I’m at on the velocity plot. My chronograph - an RCBS I’ve had for years - sucks. Waiting on getting a new one as other priorities that rank higher.

 

[bambuino]

Bambuino- I got the exploded print/parts list and ordered all the o-rings needed individual. No kit that I’m aware of.

Say rash_powder, where did you order from? How did you get the correct sizes? On the EXP-PP750, not all the o-ring sizes are listed. I would order from Shaoxing, which is easy by ordering from the diagram illustration numbers...but the 42USD cost of Fedex'ing 50 grams worth of o-rings is just a bit much.

Best regards, Mark

 

[rash_powder]

 Bambuino-

below is the shipping list from the O-ring store. After considering the minimum quantity for the different part numbers, I think I ended up with enough for twenty rebuilds. That’s for normal people, for me that’s about 10 after all the screw ups. I think it was right about $40 after shipping. Some of the sizes were not available so I got the next closest based on some help from this forum. There’s a thread somewhere.


hope this helps!

 

[bambuino]

Ur the bomb.

 

[rash_powder]

I finally got back to working on this after nearly a year - things move slowly for me. This pandemic and home life are taking a tole.

I have hit a wall and am not sure how to solve it - I think I have an idea or two, but not 100% sure as to the proper route. I have, through regulator and hammer spring adjustments, found ~440FPS. 40FPS more than I want. That is with the hammer spring out as far as possible and the regulator 3/4 turn ccw. At 7/8 turn ccw I am back up to ~470FPS. So it looks like I may only be able to bottom out at ~440FPS, unless I can lighten the striker spring, lighten the striker, or introduce additional restrictions into the air path. I do not like to modify my only factory parts as it is hard to go back if an error is made; so I will need to source parts. Would Veradium Air or Airgunarcheryfun have replacement springs and strikers? Possibly even the transfer ports?

I'm thinking I can cut the striker spring, drill the striker, or solder the transfer ports closed and re-drill them a smaller diameter. I'm not sure the smaller holes will cause less air to be used though.

Has anyone any ideas as to slow things down just a bit more? I want to maximize my shots per fill as I only have a hand pump and this is a 5m target gun.

Thanks!

 

[Hawkeye51]

Rash

You need a lighter spring or you can cut 1/2 coil off the factory spring at a time and measure the speed with the hammer spring adjustment backed all the way out. This is the easiest route. Easily reversable by getting a new spring or by adding a washer or two to the bottom of the spring.