My Bottled Prod Build

[UCChris]

Here's the build thread for my Black Friday Prod. I've been waiting on parts ever since I ordered the gun, but they've all arrived, so I can have something to show. The build parts are as follows:

* Factory shroud, breech, and grip assembly.

* .177 Mrod barrel, cut and machined by Rocker1

* Don Cothran tube, measuring 6.75" long.

* Lee545 folding stock.

* Gauntlet tank block from Umarex.

* Maxtact 9ci bottle w/ PepperBall regulator.

* DonnyFL Tanto w/ adapter.

As you can see, while still a Prod at heart, there's not much left stock on this gun. My goal was to make a lightweight bottle gun that didn't suffer from the balance issues that most bottle guns do. I contacted Don Cothran to make me a super short tube that was ready to accept a tank block. That, along with the 9ci tank I found, makes for a very compact and well balanced gun, but only leaves 1.8 cc of space (1/4") between the valve and tank block. I got some of the right Belleville washers (thanks to Jason aka nervoustrigger) and got them in the regulator. My regulator pressure should be between 1100-1500 psi, but I have no way to test for sure, other than running the hammer spring super hot so that I can see the gun fall off the reg. Here's how she looks.



I drilled the transfer port to .125", assembled the gun, and, with 7.33 JSB, it was shooting 685-700 fps. It wasn't super consistent, but was shooting a bit hotter than I expected, considering the plenum volume (1.8cc + valve volume). I noticed that the transfer port in the valve was a bit off center and was a little occluded by the transfer port seals. So I drilled out the transfer port about halfway to give room for air to flow without as much disruption. I also drilled out the face of the valve and the tank block. The valve came out real nice, but the tank block not so much, so you only get a pic of the valve.









I also pulled the regulator apart and cleaned up the face like Jason instructed in one of his recent threads about cheap regulators. After assembling, it is now shooting 560 fps, super consistently. No freaking clue why the gun lost power, but it sounds like it's related to the way the hammer is hitting the valve. I'm about to pull it apart again. Will update when I have more info.
 

[RDB]

Looking good Chris. Gotta be something simple. Threw that hammer in the mail today. If you have a lighter valve spring, toss it in while its apart. Being regulated jus needs to hold it closed when filling. Stock spring is a monster.

[UCChris]

Okay, so I did a little chrony work to see if it told us anything.

1000 psi:

721
693
687

1500-1000 psi:

723
717
698
700
697
695
697
699
702
698
699
701
696
691
691
695
692
693
691
690
688

2500 psi (all that's left in my tank):

724
709
706
708
706

So, I'm stumped. I really need the input of you regulator gurus. It's clear that there's a ton of creep. If I wait 30 seconds between shots, it wants to shoot around 725 fps. What strikes me is that the starting shots of all the strings, which are directly after filling, are within 3 fps of each other and hovering in the 725 area. So definitely creep. However, what sticks out is that the first shot at 1000 psi is 724, then it immediately drops off. I have no idea where my reg setpoint is.

Let me try to organize the timeline:

First assembly of gun, with all the custom parts and .125" TP - 700 fps when settled, around 680 when not letting the reg sit between shots. I then crank the hammer spring one full turn in and get no increase, so I back it out two full turns (1 full turn less than starting) and see no increase. So definitely running on the plateau.

I then pull the regulator apart, sand the valve seat as per Jason's post and drill out the valve and tank block. This nets me 560 fps. Stumped, I pull the grip off to see if anything is showing signs of hammer dragging or something. I notice that the rear grip screw is barely contacting the hammer spring when fully tightened down. Thinking this might be my problem, I put a washer on the rear grip screw. This gets me shooting back around 650ish fps. I then turn the hammer spring in another full turn and get 675 fps. I put in another turn and get 715 fps. Finally, I give it one more turn and I get 725 fps.

I'm confused that hogging out the valve and tank block, in addition to three full turns more of the hammer spring, is only getting me 25 fps more than before. I threw in the .009" shim that the regulator came with, so now I have )()()()()(| and that didn't give me any more speed.

I definitely have to figure out how to fix the valve seat, as the creep is ridiculous. I am wondering if that valve seat could be causing me to lose the gains that hogging out the valve/tank block would give. Considering that I started with 1.8cc and the valve volume for my plenum, drilling out as much material as I did should get me way more than 25 fps with super light 7.33 pellets...

[Pelletjunkie]

When you cleaned up the face in the reg you change the set point. Just build a reg tester. You will need an ASA remote on/off adapter, slide check and a gauge. Quit guessing before you blow a burst disc and poop your pants.

[Pelletjunkie]

I would have left the valve and tank block alone. You are only shooting a .177, no need to get crazy hogging stuff out.

[Dairyboy]

I'm wondering if the little pocket created there on the valve can be causing more problems than good. Kind of a little pocket where air can get trapped and cause turbulence.

[UCChris]

I'm wondering if the little pocket created there on the valve can be causing more problems than good. Kind of a little pocket where air can get trapped and cause turbulence.

I would be surprised if that was the case. People have been boring out the face of valves way back to when Jason and others would mill slots or cut down the QB valves to get more plenum volume. I don't know how I could screw something like that up. But then again, it is me we're talking about...

When you cleaned up the face in the reg you change the set point. Just build a reg tester. You will need an ASA remote on/off adapter, slide check and a gauge. Quit guessing before you blow a burst disc and poop your pants.

I've looked into that, but I've seen people talk about the slide checks only being rated for CO2 (~1100psi max) and the checks can get blown out by using it at higher pressures.

I would have left the valve and tank block alone. You are only shooting a .177, no need to get crazy hogging stuff out.

If I want to get 11-12 fpe out of a regulated gun with <5cc plenum, I would think I can use all the help I can get from hogging out the unnecessary space.

[Pelletjunkie]

I have been testing my Priest’s reg 140-170b. No problems. If the slide check would fail it would have to just be an air leak because it couldn’t hold back the pressure.  Not a grenade situation.

[UCChris]

I have been testing my Priest’s reg 140-170b. No problems. If the slide check would fail it would have to just be an air leak because it couldn’t hold back the pressure.  Not a grenade situation.

Right on. Did you pick up your stuff locally or online?

[Pelletjunkie]

I got it a good while ago online when I did a 2240 bottle gun. I didn’t see where you had a 12fpe goal. I also don’t like doing backwards math. I thought you being in the 700’s was a good start.

[RichH]

Reg tester parts

https://www.ebay.com/itm/CO2-FILL-ADAPTER-REMOTE-ON-OFF-DEGAS-WHEN-UNSCREW-AMERICAN-MADE/274092992837?epid=0&hash=item3fd1372945:g:3KAAAOSwE91dykiQ

https://www.ebay.com/itm/1-1-2-Utility-Pressure-Gauge-Blk-Steel-1-8-NPT-Center-Back-3000PSI/113811642803?hash=item1a7fb3d9b3:g:B2YAAOSwb6Bdgojb

[nervoustrigger]

Chris, that is a nice looking gun.  Lots of Lego blocks from lots of places to build it up just the way you want it.  I like that you converted it to .177...I've always thought it strange that Crosman never offered it. 

Where'd you buy the Maxtact 9ci bottle?  My search turned up a bunch of dead ends.

Regarding the pocket in the valve face, flow is very turbulent anyway so I don't think that's a concern.

[nervoustrigger]

Rich, just FYI, I've pointed people to the same fill adapter on ebay a few times based on another member's recommendation but then some folks reported back that the threads are bad about galling at anything above CO2 pressure.

I made mine with a stainless steel version that I drilled and tapped for a bleed screw.  I've kept my eyes open for an inexpensive off-the-shelf option but haven't run across one yet.

[UCChris]

Reg tester parts

https://www.ebay.com/itm/CO2-FILL-ADAPTER-REMOTE-ON-OFF-DEGAS-WHEN-UNSCREW-AMERICAN-MADE/274092992837?epid=0&hash=item3fd1372945:g:3KAAAOSwE91dykiQ

https://www.ebay.com/itm/1-1-2-Utility-Pressure-Gauge-Blk-Steel-1-8-NPT-Center-Back-3000PSI/113811642803?hash=item1a7fb3d9b3:g:B2YAAOSwb6Bdgojb

It just so happens that I have a really nice 6000 psi, glycerin filled gauge that I used on my SCUBA tank when I first started airgunning. I ordered the ASA part and we'll be in business. Thanks for the heads up!

Chris, that is a nice looking gun.  Lots of Lego blocks from lots of places to build it up just the way you want it.  I like that you converted it to .177...I've always thought it strange that Crosman never offered it. 

Where'd you buy the Maxtact 9ci bottle?  My search turned up a bunch of dead ends.

Regarding the pocket in the valve face, flow is very turbulent anyway so I don't think that's a concern.

Hey Jason! I was hoping you'd find this thread. Here's the bottle, a little pricey, but very worth it for the niche it fills.

https://www.magfedproshop.com/products/9citank?variant=15392168312918

I did more polishing on the face of the valve seat, but I'm still shooting 25-30 fps slow if I don't wait to let the regulator get all the way up. No idea what to do about the creep at this point.

[nervoustrigger]

I may have missed something but I didn't see where you had adjusted the hammer spring tension to the knee.  It will be sensitive to pressure variation until you do that.  Keep adding preload until you no longer get an increase in velocity.  That point may be higher than the 725fps figure you posted above, though perhaps not much more.  Then back off the hammer spring until the velocity falls to about 95 - 97% of that maximum.  For example, let's say the max velocity is 735fps...back off the hammer spring until it falls to 700-710fps.

Having said all that, if you haven't yet put at least a couple hundred pellets through it since you smoothed the valve seat, go ahead and do that first.  Having the valve cycle open and close will help wear in the surfaces so they mate better.

[UCChris]

I may have missed something but I didn't see where you had adjusted the hammer spring tension to the knee.  It will be sensitive to pressure variation until you do that.  Keep adding preload until you no longer get an increase in velocity.  That point may be higher than the 725fps figure you posted above, though perhaps not much more.  Then back off the hammer spring until the velocity falls to about 95 - 97% of that maximum.  For example, let's say the max velocity is 735fps...back off the hammer spring until it falls to 700-710fps.

Having said all that, if you haven't yet put at least a couple hundred pellets through it since you smoothed the valve seat, go ahead and do that first.  Having the valve cycle open and close will help wear in the surfaces so they mate better.

Thanks for the help Jason. I will do some adjusting and shoot it a bunch.

[RDB]

By looking at your strings again, it looks like the reg is around 1000-1100 psi. You'll be farther ahead when you can test the reg pressure. I run my 1720 at 105 bar or around 1500 psi. Possibly beings the plenum is so small your dumping all the volume from that and the reg can't refresh quick enough. You'll know more when you can test it.

[KnifeMaker]

You'll get her figured out Chris. Sure looks nice!


Knife

[Tucobenedicto]

Nice "Frankengun",if you notice creeping on the reg you can improve it slamming in a Ninja piston,i have done this on a couple of those Ninja clones with great results.

[Pelletjunkie]

Like Jason said, get some shots through it after surfacing that seat. Next time you are in there, ditch those O-Rings and replace them with a #41 and a #36. Those stock O-Rings are too temperature sensitive.