Benjamin Some Prod (and 1701P) ❤️❤️❤️

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weevil

weevil

Member
Dec 19, 2022
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Utah
Lots of high end AGs lurking around but sometimes it’s nice to do some work on one of the old faithful. In this case, a P-rod that has been out on loan for a few months, working on some rats with a neighbor. Time for a refresh, squeezing out a bit more accuracy, efficiency and noise reduction, the latter of which was attacked from the action end as much as the muzzle.

This little pellet shooter has already come a long long way from stock with a reg, lightweight hammer, .42 spring, PEEK striker, porting and a pretty dress. For the latest revision, added a PEEK poppet with a 2mm diameter stem, increased porting to .140, shimmed the stock Crosman barrel to fit more snugly in the breech, polished the crown and added a combination shroud/moderator (which won’t be discussed here in keeping with forum rules).

The reg was bumped up to 120bar, with the goal of getting 24 shots from a 220bar fill, shooting the 15.9grain Hades. Knowing the way this lady sings from all the previous work, I figured that the setting should net a peak speed of ~750 fps, which would be dialed back to 725, around 18fpe.

That turned out to be very close with peak speed of 745 fps. The hammer was then dialed back to get the speed settled at 725fps. I then added a 2mm PEEK shim to increase tension on the valve spring, dropping the speed to 720fps. That added a noticeable snap and gave a very nice string from 3100psi (scuba tank really needs a refill…):

722, 718, 718, 724, 721, 716, 720, 722, 717, 720, 721, 719, 722, 720, 716, 722, 719, 719, 720, 718, 719, 717, 712, 693

Just dropping off the reg on shot #23, but should be good with a 3200psi fill. Kind of an arbitrary goal of getting 3 x 8-shot mags. Silly, considering that I just ordered two new 10-shot mags. The originals seem to have gotten a little gritty.

Anyway, as those in the know will know, the PEEK poppet is a real winner here, dropping the requirement for hammer and yielding a really snappy and quiet shot cycle. The shimming of the barrel into the breech seems to have tightened up the poi in the horizontal plane.

Here she is, sporting the Optisan 6, sat on her favorite rice bag. I’m expecting big things from this little gun in the accuracy testing tomorrow.

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IMG_0906.jpeg

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Thanks for sharing your build! Prods are so much fun to build and work on. I’m tuning one now, it’s going in the same wood stock. It’s my first time ever really tuning anything. I did a b Staley with 0.42 HS and .110 TP on it. I can only get two real good mags on my tune so far(about 700-710fps w/ 14.3). I can get some nice looking strings but the fps start dropping fast around 2000psi. The weather even seems to be affecting the BSM some. I might have to go the regulated route next.

Happy shooting
Rob
 
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Nice looking gun. My Prod was my first PCP and still one of my favorites. It's taken 17 squirrels for me so far. I think it's current tune is a 3000 fill, .111 transfer port, 4 Bstaley O-rings, .042 hammer spring, 6.75 turns on the hammer spring, 1.35 turns on the hammer travel screw,. That gives me an average velocity of 735 fps on 14.66 grain copper plated FTTs for 20 shots with a 39 fps ES and about 17.5 fpe. I'm pretty sure I shot over 190 on the 30 yard challenge with it. It is consistently accurate even if it has not been shot in months. Never needed any repairs. No need at my house for a Notos.
 
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RobBonnell89 said:
Thanks for sharing your build! Prods are so much fun to build and work on. I’m tuning one now, it’s going in the same wood stock. It’s my first time ever really tuning anything. I did a b Staley with 0.42 HS and .110 TP on it. I can only get two real good mags on my tune so far(about 700-710fps w/ 14.3). I can get some nice looking strings but the fps start dropping fast around 2000psi. The weather even seems to be affecting the BSM some. I might have to go the regulated route next.

Happy shooting
Rob
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Hi Rob,

Funny you should mention that - I found 2 Orings in my air tube between hammer and valve that I must have forgotten to remove when I switched from the bstayley to the reg!

I could never get the bstayley right. It was a game changer to switch to a Huma reg and the 20 gram hammer from Hill airgun. No more bounce, major accuracy improvement and no loss of shots. The only minor downside is the loss of the gauge. I replaced the gauge block with the supplied Huma plenum, because I couldn’t get the gun to seal with the block left in. Anyway, I fill to 3200 and know that I have 24 shots.
 
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Nice work there sir! I too am a big fan of the P-Rod. If you don't mind divulging your source(s) where did you get that shroud and the peek poppet?

I am running two different P-Rods, one with a bottle feeding through the gauge port, the other one with a Fortitude tube, and both sport M-Rod 20" barrels and JSAR balanced valves. Not trying to hijack, just sharing some enthusiasm. ROCK ON!
 
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weevil said:
Hi Rob,

Funny you should mention that - I found 2 Orings in my air tube between hammer and valve that I must have forgotten to remove when I switched from the bstayley to the reg!

I could never get the bstayley right. It was a game changer to switch to a Huma reg and the 20 gram hammer from Hill airgun. No more bounce, major accuracy improvement and no loss of shots. The only minor downside is the loss of the gauge. I replaced the gauge block with the supplied Huma plenum, because I couldn’t get the gun to seal with the block left in. Anyway, I fill to 3200 and know that I have 24 shots.
Click to expand...
Thanks I might go that route then. Tim said guys have good luck with just that lighter hammer even. Maybe I’ll try that first and I’ll have it if I go regulated. I’m pretty sure it’s the orings giving me little inconsistencies. If it’s 70 out it shoots great.
Both my prods are shooters and I love them for dog walk carry.
 
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SteveV said:
Nice work there sir! I too am a big fan of the P-Rod. If you don't mind divulging your source(s) where did you get that shroud and the peek poppet?

I am running two different P-Rods, one with a bottle feeding through the gauge port, the other one with a Fortitude tube, and both sport M-Rod 20" barrels and JSAR balanced valves. Not trying to hijack, just sharing some enthusiasm. ROCK ON!
Click to expand...
Steve,

The shroud is home made but off limits for discussion due to forum rules. The PEEK poppet is also home made and I’ll post something later on the fabrication.
 
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weevil said:
Lots of high end AGs lurking around but sometimes it’s nice to do some work on one of the old faithful. In this case, a P-rod that has been out on loan for a few months, working on some rats with a neighbor. Time for a refresh, squeezing out a bit more accuracy, efficiency and noise reduction, the latter of which was attacked from the action end as much as the muzzle.

This little pellet shooter has already come a long long way from stock with a reg, lightweight hammer, .42 spring, PEEK striker, porting and a pretty dress. For the latest revision, added a PEEK poppet with a 2mm diameter stem, increased porting to .140, shimmed the stock Crosman barrel to fit more snugly in the breech, polished the crown and added a combination shroud/moderator (which won’t be discussed here in keeping with forum rules).

The reg was bumped up to 120bar, with the goal of getting 24 shots from a 220bar fill, shooting the 15.9grain Hades. Knowing the way this lady sings from all the previous work, I figured that the setting should net a peak speed of ~750 fps, which would be dialed back to 725, around 18fpe.

That turned out to be very close with peak speed of 745 fps. The hammer was then dialed back to get the speed settled at 725fps. I then added a 2mm PEEK shim to increase tension on the valve spring, dropping the speed to 720fps. That added a noticeable snap and gave a very nice string from 3100psi (scuba tank really needs a refill…):

722, 718, 718, 724, 721, 716, 720, 722, 717, 720, 721, 719, 722, 720, 716, 722, 719, 719, 720, 718, 719, 717, 712, 693

Just dropping off the reg on shot #23, but should be good with a 3200psi fill. Kind of an arbitrary goal of getting 3 x 8-shot mags. Silly, considering that I just ordered two new 10-shot mags. The originals seem to have gotten a little gritty.

Anyway, as those in the know will know, the PEEK poppet is a real winner here, dropping the requirement for hammer and yielding a really snappy and quiet shot cycle. The shimming of the barrel into the breech seems to have tightened up the poi in the horizontal plane.

Here she is, sporting the Optisan 6, sat on her favorite rice bag. I’m expecting big things from this little gun in the accuracy testing tomorrow.

View attachment 503107View attachment 503108
View attachment 503109
Click to expand...
Wow! She’s a beaut Clark!
 
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Calm morning for testing with a couple duct seal targets at 30 and 42 yards with Hades at 720fps. Jim mentioned H&N FTT copper coated pellets. Those were the most accurate when the Prod was in relatively stock form. I tested scads of pellet types after adding the reg etc and found that Hades and standard JSB 15.9 grain were equal best.

Here are magfuls, 8 shots each at 30 and 42 yards:

IMG_0908.jpeg


IMG_0909.jpeg
 
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Now, this is perfectly acceptable, especially compared to how it used to shoot and I have no doubt that it’ll work for rats out to 50y. However, the horizontal stringing is still there, clearly visible with the 30y shots. I know it’s not the barrel mounting because it’s rock solid with the tungsten leaf shim. Perhaps it’s some harmonic movement of the barrel during the shot. I don’t have the option to tension but could print a barrel band.

However, there’s one more thing. JTS pellets. I didn’t have those during the last round of testing and they were fantastic in my Katran SC, shooting at just a little higher power…
 
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I’ll take that thanks - looks like she has a new favorite pellet. What’s more, the grittiness I mentioned that I thought was the magazines is gone. These load very smoothly and perhaps it’s my imagination but the shot cycle and report seems a little crisper. It would be interesting to chrono a string but first, I’m gonna talk PEEK poppets.
 
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PEEK poppets: one of those little things with big benefits. Due to the high compressive strength of PEEK, the chief advantage is that they are easier for the hammer to knock open. Less hammer strike provides a nicer shot cycle, making the AG easier to shoot accurately. Quieter action noise is a side benefit. Another advantage can be gained by reducing the diameter of the poppet stem, which effectively increases the valve throat area and decreases the force of closure, although the latter is not necessarily an advantage.

PEEK poppets are relatively easy to make if you have a lathe. While they can be made using hand tools, there are a couple of aspects of the fabrication that are tricky and can lead to a high frequency of failure. Namely, the drilling of a hole for the stem, perfectly centered in the PEEK rod. Then the polishing of the poppet surface that forms a seal with the face of the valve. I’m not going to go through the whole procedure of making the poppet from PEEK rod and a steel drill blank (you can find that info elsewhere) but I will show you a couple 3D printed doodads that I use to overcome the problems I highlighted earlier, allowing me to make a perfect poppet that seals at well below 100bar. Part of the credit for this idea comes from @nervoustrig who demoed the use of a wooden block to polish the surface of a poppet.

Here’s a picture of the two jigs that I print and use.

IMG_0913.jpeg


First, on the left we have a jig that holds very tightly on one side the “raw” PEEK rod. It then has a hole on the other end for the drill bit to drill a perfectly centered hole in the PEEK rod for the stem.

(After drilling the stem gets interference fit, the rod is cut to size and then the poppet can be formed by cutting or sanding while chucked in a drill or, in my case, a $150 micro lathe )

Then on the right is a jig that has a hole for the stem. The surface of the jig can be printed flat or concave, depending on need. The poppet is then sanded with progressively finer 3M abrasive paper (shown between the jigs) by spinning it by hand on the jig with a piece of paper under the poppet.
 
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weevil said:
Lots of high end AGs lurking around but sometimes it’s nice to do some work on one of the old faithful. In this case, a P-rod that has been out on loan for a few months, working on some rats with a neighbor. Time for a refresh, squeezing out a bit more accuracy, efficiency and noise reduction, the latter of which was attacked from the action end as much as the muzzle.

This little pellet shooter has already come a long long way from stock with a reg, lightweight hammer, .42 spring, PEEK striker, porting and a pretty dress. For the latest revision, added a PEEK poppet with a 2mm diameter stem, increased porting to .140, shimmed the stock Crosman barrel to fit more snugly in the breech, polished the crown and added a combination shroud/moderator (which won’t be discussed here in keeping with forum rules).

The reg was bumped up to 120bar, with the goal of getting 24 shots from a 220bar fill, shooting the 15.9grain Hades. Knowing the way this lady sings from all the previous work, I figured that the setting should net a peak speed of ~750 fps, which would be dialed back to 725, around 18fpe.

That turned out to be very close with peak speed of 745 fps. The hammer was then dialed back to get the speed settled at 725fps. I then added a 2mm PEEK shim to increase tension on the valve spring, dropping the speed to 720fps. That added a noticeable snap and gave a very nice string from 3100psi (scuba tank really needs a refill…):

722, 718, 718, 724, 721, 716, 720, 722, 717, 720, 721, 719, 722, 720, 716, 722, 719, 719, 720, 718, 719, 717, 712, 693

Just dropping off the reg on shot #23, but should be good with a 3200psi fill. Kind of an arbitrary goal of getting 3 x 8-shot mags. Silly, considering that I just ordered two new 10-shot mags. The originals seem to have gotten a little gritty.

Anyway, as those in the know will know, the PEEK poppet is a real winner here, dropping the requirement for hammer and yielding a really snappy and quiet shot cycle. The shimming of the barrel into the breech seems to have tightened up the poi in the horizontal plane.

Here she is, sporting the Optisan 6, sat on her favorite rice bag. I’m expecting big things from this little gun in the accuracy testing tomorrow.

View attachment 503107View attachment 503108
View attachment 503109
Click to expand...
I really love how this looks
 
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