Tried the O rings, Prod results

[LeadandAirFun]

Here is what I learned:

With the original tune using CPHP in 14.3gr, 6 1/2 HS and 3/4 HT = 365fps @ 3000psi with these o rings.

Without 425fps so I know they are making contact with the hammer. There does seem to be less spring "twang" and/or valve chatter in the gun.



To get the numbers back up to stock and over where it was I had to crank the HS to 8 and the HT to 1 1/2. The first shot @ 3000 was 437. Like stock it started to wake up at about 2300 peaking at 609fps and like stock it has a curve (slightly flatter) with the shot count remaining the same down to 1000; 64.



I welcome all thoughts and comments. How much difference does smoothing off the edges of the ports make? I've done port work old VWs, not that there is much comparison, but I know smooth air flow helps with performance

 

[dizzums]

smoothing i doubt will do much .. simply installing a larger tp though, got mine in the 700 range ..

 

[SqrlHntr]

Thats pretty low to me. Sounds like the valve is barely opening before the hammer face hits the o-rings. Try less hammer spring, and more throw, adding a 1/4 turn at a time to the throw while over a chrony. The idea is to have the striker contact the stem and the oring acts as an over travel stop for the hammer, so the valve stem only travels a certain distance, within reason. What sounds like is happening is the striker is too close to the hammer and cant open the valve long enough before the hammer gets stopped and the valve closes. The extra hammer spring tension you have is trying to compensate and compress the orings to open the valve more. A larger transfer port will give you some more power, helps to match and enlarge the barrel port as well. Smoothing prob does not help to any noticeable effdct, Nervoustrig commented on this and existing air turbulence in another post. Also make sure you have a nice coat of dry lube in the hammer area. Polishing the hammer area doesn't hurt either. Just my 2 cents, hope it helps!

 

[LeadandAirFun]

Dizzums, how much did the lager tp affect shot count? Also what size did you use, Im liking the sound of 700 range! Thanks for the insight SqrlHntr, Ill give those adjustments a shot tonight and post the results.

 

[Old-School]

I’m with SqrlHntr. I haven’t finished tuning my Prod post BStaley mod, but found I had to back off my hammer spring to 5.5 and increase hammer throw to 1.5 to get above 700fps using 14.3 CPHPs. With HS at 6.5 and HT at 0.5, it was shooting in the low 600s at 2800psi. Increasing HS only made things worse.

 

[SqrlHntr]

If you remove the trigger group and peek up into the hammer area, you might be able to see the the striker and valve stem, a good place to start for me was the striker as close to the valve stem without touching. As i remember the tune i settled on for factory parts was like barely a 1/10th of a striker turn from that point of making contact and hammer load was around 5.

 

[LeadandAirFun]

Very cool to know SqrlHntr, had no idea I could have a peak at that, thanks! Did some shooting tonight and had a big Hill pump let down. It was one of those things where my head dropped and shoulders slumped, the word I said starts with an f. Never use a Mk 5 pump without the air drier! This is what I get for going the cheaper 'pump only' route; hindsight is always 20/20! The outer tube is steel and will rust from condensation. I noticed a "crunchy" feeling pumping and brown substance around the pressure relief. Here's the horror show

So now I need to learn how to take the whole pump down to parts. I like learning my equipment but not un-neededly. I looked in the fitting of the gun VERY closely and didn't see any residue thankfully. But anyway, lightening the hammer did help. After some tweeking finding where the gun seemed happiest after a dozen or so combinations and twice as many pellets I got to 7 1/2hs with 1ht to get 612fps @ 1800psi. Topped off to 2500, 525 which seems to be ahead of the power curve for this gun even stock. Found the pump issue, got disgusted and quit shooting. I'll have a look at the valve situation, if it checks out I'll give that tune of yours a shot tomorrow and post the results. Now I have to learn all the intricacies my pump, glad I have the cheapo sitting.

 

[nobody1]

It took me a while but I am finally happy with my Prod.

With CPHP 14.3 grains now it shoots from 685 FPS to 720 FPS and from 3300 PSI to 2100 PSI for 32 shots.



The mods I made:

• BStaley mod, 4 orings (oring size is important)

These are great step by step instructions for doing the BStaley mod with lots of photos: 

https://www.tapatalk.com/groups/yellow/bstaley-buffer-mod-picstory-for-a-p-rod-t201906.html

• drilled transfer port to 0.12"
• installed a much stronger hammer spring

This is the spring I am using (outer diameter 7mm, wire diameter 1mm, length 100mm):
https://www.aliexpress.com/item/4000434419055.html

I cut the 100mm shorter and shorter several times until the gun started cocking.



It took me a lot of time (at least 12 hours on various occasions), shots over the chrony and trial and error.

The hammer stroke adjustment screw has the tendency to screw itself in, so I replaced the acetal pin.

Even now the velocity seems to drop a few FPS after a shooting session because of that screw very slowly screwing itself in and reducing the hammer stroke.