.257 cal Monocoque PCP

[rsterne]

Today, I took apart a Ninja 4500 psi "high-pressure" regulator and rebuilt it for inline use.... It looks like these other ones I have done previoulsly....



The modifications I made are as follows.... Do this only if you are competent working around HPA, and at your own risk.... Other regulator brands (or clones) may not be acceptable/safe when doing these modifications.... although if rated at 4500 psi input, and properly engineered to withstand a failure to that pressure, they should be....

1. Completely disassemble the regulator, removing both burst discs, the male Foster and the gauge from the reg. body.
2. Cut off the threaded stem that screws into the tank just below the safety vent hole.
3. Drill the bottom of the body to 11/32" until you just touch the three cross holes that pass air to the fill, gauge, and HP burst disc, and tap 1/8"-27 NPT.
4. Deburr and use compressed air to blow all debris and chips out of the regulator body, and install a plug, using Teflon tape to seal it.
5. Reinstall the male Foster (with NO check valve) and gauge, and install burst discs of the appropriate rating for the inlet and outlet pressures.
6. Remove the pin valve from the bonnet, and drill through 11/32" and tap 18"-27 NPT.  Remove all debris and chips with compressed air.
7. Install a female Foster in the bonnet.  I used a close hex nipple because I didn't have a female Foster with male threads.  Both Fosters should be rated for 4500 psi.
8. Install new O-rings on the regulator piston.  I would recommend using a Ninja rebuild kit from Mac1 Airguns, which comes with 90D Mil-Spec Urethane O-rings.
9. Install a Belleville washer stack appropriate to the pressure range you need, with appropriate shims, on the piston.
10. Install the piston in the reg. body and screw on the bonnet.
11. On the output side, attach an accurate gauge equipped with a bleed valve to the female Foster.
12. Fill slowly through the male Foster using a tank or pump, to 1000 psi, and check for leaks.  Repair if necessary.
13. Slowly increase the pressure at the inlet, while watching the gauge.  If you increase the pressure too close to the rating of the outlet burst disk it will fail.
14. If the burst disc fails, change your shorts, then change the disc, reduce the shimming in the regulator, and repeat.
15. If the indicated output pressure is too low, shut off the tank, bleed the system, and increase the thickness of the shims. If too high, remove shims.
16. When you have the regulator adjusted to the setpoint you want, "burp" the bleed valve a few times to settle the needle, and the reg. and double check the pressure.
17. Once you have the regulator adjusted the way you want, close the tank valve, and bleed the system.  Record your Belleville stack and shims for future reference.
18. You can now tether your gun to the output side of the regulator with a HP hose, and when you turn on your tank, your gun will fill to the setpoint pressure.
19. If your gun has a pressure gauge, fill slowly and double check that its gauge is close to what you read on your quality gauge.  They may not agree exactly.
20. Enjoy shooting you gun tethered to your tank.  Ideally, the burst disc on the output side of the regulator should be close to, or only slightly above, the MSWP of your PCP, in case the regulator fails.

Although you have to change shims to alter the regulator setpoint, this makes a great inline regulator at far lower cost than the $300 plus adjustable variety....  The regulator for my Monocoque is set at 3800 psi.... This required a very unusual Belleville stack to achieve that high output pressure, consisting of five pairs of Bellevilles, with each pair consisting of a 0.047" nested inside a 0.032".... and then two thick Ninja 0.020" (red) shims, arranged like this....  The flat shims are inside the regulator body, with the opposite end of the stack against the large end of the piston....

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There are two BIG warnings about using this setup.... There is very little total travel, only 0.060" from loose to fully collapsed.... The pairs of Bellevilles take a huge amount of force to drive them flat, about 860 lbs., and that only takes 0.012" of movement per pair.... This means that EVERY 0.001" of shims changes the output pressure by about 90 psi.... Just a few thou of shims can make the regulator go from 3000 psi to not regulating at all, and passing the full tank pressure through to the output.... Most Belleville stacks are not this harsh to adjust, but when you need to go to high pressures, they get very fussy.... My regulator has a steel bonnet, I don't know if the aluminum bonnets found on some regulators are strong enough.... but Ninja sell "high pressure" regulators with the output set as high as 3000 psi, and having a 5K burst disc on the output side.... If they failed, they would pass the 4500 psi tank pressure through to the output side, and I trust Ninja to know what they are doing.... so I personally have no problem with such a high setpoint.... but I am NOT recommending that you do the same.... nor do I know if "clones" are engineered to the same standards, even if rated at 4500 psi.... as many do not have high enough output pressures to require a 5K output burst disc.... and only come with a 3K.... Substituting a higher rated output side burst disc may be pushing the safety of any regulator not so designed....

Bob

[Buldawg76]

Bob
I have found that when adjusting the output pressure on my Ninja regs used with my 13ci tanks on the QBs that I get a increase of 50 psi for every .005" shim I install. I am only going to a max of 1500 psi so I am just wondering when you say a increase of 90 psi for every .001" shim is that because you are setting at a much higher pressure.

Mine are the Ninja pro SHP regs if that makes any difference also.

mike

[MJP]

Bob you should have added a warning, do not ever try this with the generic Chinese eBay or any cheapo knockoffs out there!

Marko

[rsterne]

Mike, it is because the "paired" Bellevilles are so stiff, and the total compression only 0.060" that makes the pressure very sensitive to shimming....

Marko, I did state Ninja regulators, but I added a warning about that, thank you....

Bob

[Buldawg76]

Bob
Ok that makes sense and some of the bellevilles are .047s and .032s whereas mine are .032s and .023s in the lower pressure regs. So I can see how it would be more sensitive and react with a greater change in pressure.

Mike

[MJP]

Bob, when are we going to see some long distance groups?
I have been following this from the start and groups would be interesting.

Marko

[rsterne]

The snow is melting fast here, Marco.... I am "aiming" for sometime next month for initial tests.... Cross your fingers....

Bob

[YEMX]

(Please correct me and PM if I'm wrong, not trying to thread-jack)

Which Ninja Reg are you using, I'm seeing two on fleabay: Standard 4500 psi adjustable, the V2 4500 (NOT SLP).  For uh, scientific purposes...   

And uh, what would the stack look like for say... 2800 psi output?

[rsterne]

Use the Ninja high-pressure reg (the one with the gold body, and 4500 psi input).... the same as the one they use in their 90 CI 4500 psi HPA fill stations to fill PCPs up to 3000 psi.... You can buy then from Ninja already adjusted in 200 psi increments, up to 3000 psi (ie 2600, 2800, 3000).... Most of the Belleville stacks for that pressure consist of the 0.047" (thickest) Bellevilles in series, either 8 or 9 or them, and some flat shims.... arranged like this....

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If you use 9, the additional one would be on the right, like this.... ) .... against the piston.... the flat shims are against the reg. body....

9 of the 0.047" barely fit inside the Ninja regulator without any shims, and are nearly flat (ie think of coil bound for a spring) at about 2900 (plus/minus 100) psi, so not much adjustment.... You are probably better to use 8 and a stack of shims to get more adjustment range....

Bob

[YEMX]

Excellent!! As always, thank you Bob, for the info!!

[rsterne]

Well, a year after this project came to a grinding halt, I finally got a day to take her out and let her stretch her legs a bit.... I built a new shooting bench, and the Monocoque was the first gun to try it out at 100 yards.... Here is a pic of the setup....



and here is a photo of the range, currently set up for 100 yards....



The field I am set up in has the ability for me to move the bench back to 300 yards, or pretty much anything in between.... The rancher I shoot Varmints for allows me to leave the bench and target stand in his field.... I have wind flags on stakes, currently at 25, 50, and 75 yards.... and recently purchased an anemometer that I keep on the bench with me....

The Monocoque was tethered to my Great White by a 3800 psi regulator, and I shot enough to use 1000 psi from the tank today.... I had 12 different bullets to try, or rather 4 different bullets, and three diameters of each, 0.256", 0.257", and 0.258".... The bullets were the HP and FN versions of my two heaviest Bob's Boattails from NOE.... The bullets tested were a 98 gr. HP, a 100 gr. FN, a 109 gr. HP, and an 113 gr. FN.... All bullets were cast in 2% tin....

The Millet scope is mounted on a Picatinny rail that I milled to angle the scope downwards, to hopefully center the POI at 100 yards with the scope centered, and it worked perfectly.... I was within 4" at 100 yards, and only need to tweak the turrets a bit to roughly center me with the 109 gr. bullets.... The 113 gr. were a bit low, and the 98 and 100 gr. were a few inches high, because there is an 80 fps difference between the lightest bullet, at 960 fps, and the heaviest, at 880 fps.... The first targets were 3 shots groups, intended just to prove that the POI was intended, and one of those was the best group of the day....



I saw a pretty clear trend, with the heavier bullets begin more accurate, and the smallest diameter the least accurate.... I'm not thrilled with the average 5-shot groups I shot today, but that 3-shot above, at 1.12", show that the gun has promise.... One thing is clear, the holes in the target are perfectly round, showing no sign of yaw, so the 7" twist is sufficient even for the longest bullets....

Bob

[MJP]

Well you finally got to shoot her.
The tight twist is going to be interesting to find the perfect bullet and pressure combination.
Gun looks awesome for sure!

Marko

[MJP]

Hi Bob, digging this old thread up. Have you shot her more and found the working combination?
Would be nice to see more testing, if it will group or not?

Marko

[rsterne]

Marko, your frustration at my lack of time to shoot pales by comparison to my frustration.... As soon as spring comes and the snow melts on the range, our Motel gets busy and I have to be here.... There are really no days off during tourist season (we are open 7 days a week, only my wife and I to run the place), which goes until mid-November, when the snow hits again.... My shop time is from then until April, but my summer shooting time is scarce.... The good news is that we will be closing the Motel in about 3 years, so the summer of 2021 I plan to spend a LOT of time shooting all the project guns that have been piling up from each winter's work.... I never thought I would have so little time to shoot, but at least there is light at the end of the tunnel now....

The only shooting the Monocoque got I reported above.... and that was really just proof of concept.... yeah it works!.... I have four bullet weights to try (2 FN and 2 HP).... and the sizing dies to go from a couple thou under bore diameter to a couple thou over.... In addition, I have the barrel tension adjustment to play with.... and of course I can adjust the velocity also.... so there is almost an infinite combination of factors to sort through to find the accuracy I hope is lurking there.... Indeed, the "Impossible just takes a little bit longer to achieve.".... 

Thanks for your interest.... it does help to motivate.... 

Bob

[bigben11]

I am looking to remove my air rifle pressure gauge(don't need it).  Is there anything available that I can use that has the same thread that can close that opening?

Does any one know what the standard thread size is on gauges.

[rsterne]

Most PCP gauges are 1/8"-27 NPT, so a standard pipe plug should work.... However, if your gauge is sealed with an O-ring instead of Teflon thread tape, it is likely a straight thread.... I would suggest checking the pitch with a thread gauge to make sure it is 27 TPI and tapered before just winding a pipe plug in the hole....

Bob