Marauder Semi-auto power tune mods

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Once again extremely helpful and thank you! I will take all the advice I can get. Im happy to be the canary in the coal mine here. Replacement parts are available and hopefully (aside from catastrophic stupidity on my part) worst case scenario I go back to stock with a few broken magazines. 

I ordered more mags, extra Orings, and a few other parts from Crosman today. I nicked one of the ORings on the gauge port test fitting a 3D printed spacer (modeled after that nice blue aluminum piece you have in your picture above) using thick annealed PEKK. Pretty hard stuff for thermoplastic, should be at least as strong as the thin aluminum stock spacer. I cant reassemble until ORings arrive in a few days. Per your suggestion, this will go back together stock to get a shot string where the reg drops off before drilling anything. 

Is it worth relocating the reg to the other side of the gauge block first?

I was planning on using the thin stock aluminum and my ORinged PEKK spacer to maintain correct distancing from the gauge port to the valve. If I do that first I will see reg pressure on the gauge and will be able to tell what stock is in PSI and FPS, and the impact of a larger plenum on subsequent steps I think? Otherwise I am guessing at what 200 PSI in reg adjustment is. Any idea how much to twist the nylon nut for a ballpark 200 psi? 

Please let me know if I should get some of the Crosman pellets or are the JSBs ok?

The simple "push in the button" suggestion is great, I missed that one. I could print a replacement or addition to the spring side of the button that acts like a shim and holds the spring in place like stock if pushing it in works. Thanks again!
 
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Jumping to the reg upstream of the gauge block will require a permenent mod of drilling a vent hole in the air tube. It will also take it from a too small plenum to larger than needed one. It will require lowering the reg pressure. I was trying to test without making that kind of change. Instead of inching closer to the edge of the cliff, you prefer to jump. ;)

If you used the JSB long enough and have no cycling issues, should be fine. The crosmans domes is what the gun tested with and what cycle the best. JSB 15.89 domes cycle well for me, but get occasional low powered shots. The cycling action with the soft lead pellet, pushes them down the barrel. This may be just my barrel issue, though.

Never thought of a 3D printed bridge. I have used 3D printed cross-flow de-pingers. This will have 3000psi load on it though. I'd like to see a picture.

These regs have some "loctite" to keep the adjuster from moving. And they will move if not. If they fall below reg set-point there is essentially no spring pressure to hold the adjuster from not moving. If you haven't, put a witness mark on the plastic adjuster, and the edge of the reg body, for the default position/adjustment.

Buy a bag of 100 -118 BN O-rings 70D.

If you print a new load assist button, leave a hole in the end. Then you can use a small rod to see if the bolt closed all the way and if not, a more positive way to seat it fully closed.




 
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Gotcha. The regulator adjustment will stay in the order you suggested. It would be interesting to have the info from the experiments sequentially anyway. 

The JSB 18.1 never failed to cycle. I tried some heavier 25.5 JSB Diabolo Redesign and the rifle never choked but the FPS dropped a lot and did not seem consistent so I stopped after a few shots and pulled the magazine. 

Great idea about the hollow tube in the forward assist! Ill try to get close to the stock position with the print. I was a little nervous about the printed bridge, but looking at the thin aluminum tubing spacer I bet that would fail first. You bring up a good point though. I could not figure out how to pressure test the bridge so I tried it in between the floor jack and the car frame and jacked up my car. Gauged a little but held the weight fine. Maybe thats 2000 lbs of force. With the reg set high the differential pressure would be even less right? Not exactly 3x the load but still. Glad you mentioned this. I made the walls thicker and took a few millimeters off the bridge to use stainless washers to spread the load a little from the thin spacer tube. The PEKK stuff is not PLA at all. 

Thanks for the Oring part! Way better than buying them one at a time... 

Take a look and let me know?
 
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C66FA12D-793F-46D4-AAA9-7CF553AF4477.1640326371.jpeg
94B429A6-862F-44FB-B6D7-87D53A081246.1640326373.jpeg
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After closer inspection one of the Oring grooves was a little compressed. Using the washers should fix that. But, as it stands now, the bridge will only have a purpose later if the reg is moved or replaced with a Huma or something. It would be nice to have gauges for air tube pressure and regulated pressure, if possible, but not absolutely needed. It might be possible to drill out the vent hole for another gauge for that, or use a filler gauge, but there is a lot to do first. 
 
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I'm 3D printer illiterate. So, know nothing of materials and methods to make structurally sound pieces. It is 3K psi, because it is only anchored at the valve side. When we have the data from the tests, we can take another look, and also calc out the plenum size. I did run a couple failure scenerios through my head, and don't see a safety issue, but need to look closer. Leaks may be more of the issue.

For the regulator adjustments, I'm looking for the turn/pressure info I had. I think going 1/4 turn CCW for each test is going to be fine. We will have to use the declining string to ID the set-point, but should be close enough. I will be looking more at the FPE produced, too. I'm not expecting to go to the third adjustment. Unlikely there is enough hammer spring adjustment to open valve. Changing hammer spring could impact the hammer cocking of the SAM.

On the load assist test, what I am hoping to see is no cycling issues and some increase in fps. After doing the lighter JSB's, thinking the 25g ones might tell us more. Maybe one mag in normal position, and one with it pushed in. I'll be able to test mine for this, as well. 

From the schematics, there looks to be two springs. A buffer spring behind the load assist and bolt spring in front. Have you tried to remove the cap that holds the button in place?

If you currently have it all apart and waiting on crosman parts, I'd like to calculate the existing plenum.

1. Can you get the liquid volume of the valve? Distance from center of valve screw to inlet end of valve? 

2. OD, ID and length of aluminum spacer?

3. The ODs of the reg and length of each step? Distance between O-rings?

4. Gauge block ID and length? Distance between O-rings?


 
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Thanks for clarifying the PSI load. I am curious about leaks also. The hammer cocking mechanism seems like a combination of bounce, rebound from the valve spring, and air pressure closing the valve all combined to push the hammer back to cocked. Getting more hammer force looks like another balancing act.


I pulled the cap off yesterday to get measurements of the forward assist button. You are exactly right, longer bolt spring and a short wave spring as the buffer. I put a 3mm hole in the middle so a little Allen wrench will work to check seating depth. Not exactly pretty but should be functional. 
E5560282-7236-4102-88E8-518CB8EEC57D.1640360628.jpeg


I’ll get the measurements for the plenum pieces shortly. 
 
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1. Can you get the liquid volume of the valve?

I pulled the c clip to measure the available inside of the cylinder, measurements are in inches and volume is in CCs (D=0.497 L=.997)=3.03 cc

The volume of the cap tube that inside the the cylinder =.618 cc and the volume of the rubber part of the valve stem= .468 cc. I overestimated the plug part of the valve stem to balllpark the spring volume. My best guess is the abailable volume is

3.03-(.618+.465)=1.947 cc

2. OD, ID and length of aluminum spacer?

In inches, OD=1.000 ID=.915

The length of the spacer tube not taken by the end of the regulator L=.916. So the available volume is about 9.87 cc

3. The ODs of the reg and length of each step? Distance between O-rings?

OD1=.877 L1=.634

OD2=1.050 L2=.788

OD3=.875 L=.368 (this part is in the spacer tube so I subtracted it above)

ORing Inside the groove to inside the groove =.373

outside to outside =.626

4. Gauge block ID and length? Distance between O-rings

ID=.365 L=.570

Outside thickness=.192

ORing Groove inside to inside=.580

ORing groove outside to outside =.840

Comparison of the printed forward assist and the OEM:

F42840CC-D91D-4C15-BB34-869593C85AC4.1640382333.jpeg


I’ll pm you a number to text so I’m not holding you up. Hope this helps, text if I missed something?






 
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A question about the gauge block. Is it harmless to drill out some of the center of the piece so perhaps an aftermarket regulator could stick its nose through there if necessary?
Click to expand...

Probably not. You can't break into where the gauge adapter O-ring sits. You can hog it out in a "D" shape, but that won't give you access to a reg.



It would be easy to replace gauge block with a Huma w/gauge block and not have to drill a vent hole. I am concerned that the Huma will not recharge as fast as the crosman reg, though.
 
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OK Thanks. I have been thinking about options to get tube and regulated pressure gauges. Not totally opposed to drilling the tube and stock to fit, maybe around the existing bleed hole if everything works. Great point about recharge speed. Huma regulator worked perfectly for me previously and would be really happy to get another one. It sounds like Lane has a "fast flow" reg system specifically for semi/full auto. Looking forward to getting this thing back together to start testing. 

Have a very merry Christmas!
 
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That sounds like the right ballpark to me. Everything could be measured with water, If you think that is necessary, but it seems like the conclusion will be it is pretty small. I was hoping to get 40+ fpe but that might not be realistic. 

There are some good resources for determining optimum plenum size here. Are we looking at a ballpark 30 cc plenum requires to make that work with a 2500 psi regulator setting? 
 
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I redid the calculations this AM and came up with same. :) 0.7476ci or 12.3cc's So about a 14cc plenum, which is more than I thought it would be.

The O-ring gap on the regulator is too narrow to use the existing gauge hole for the vent. So, reusing the crosman reg will mean drilling a new vent and will be upstream of gauge block. So, I'm not going to try going bigger than that.

My target is 30FPE and think 40 will be a hard to achieve, but that is what the testing should help evaluate. Getting ahead trying to calc new plenum with bridge.



PS: Not following my own advice, I calculated another 9cc of plenum going to a Hill gauge block (0.666" ID X 1.470" L) for the bridge, along with the ID of the SAM gauge block. The aluminum spacer would be slightly shorter. Another 1.5cc around the outlet section of the crosman reg. So a conservative 10cc adder for 24cc plenum. If you need/want more, can add aluminum spacer between SAM gauge block and crosman reg, moving it further up the air tube.


 
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Is it possible to move the reg to the other side of the gauge block and vent by removing the lower Oring on the reg and the upper Oring on the gauge block so the reg vents out the gauge hole be a problem? That would still require an Oring spacer to seal the vent hole in the air tube and make up the space but that would provide a lot of plenum space. Is this possible or have I gone off the deep end here?

Not to take this too far off topic, but I got my son an Air Venturi Avenger for Christmas. For the price it is hard to believe how it shoots. This is not a fair comparison between a single shot and a semi auto, but the external adjustable reg and very high pressure tube add a lot of flexibility to what that will shoot accurately. I guess I am still aiming for the 40FPE neighborhood, if that means adding an aftermarket regulator with an incorporated gauge port that might be the answer to get the plenum volume needed. 

The replacement parts from Crosman to reassemble and start testing should be here in a day or two. They usually ship quickly but holiday delays would not be surprising.
 
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If there was a plenum, like what Huma has for the disco/maximus/prod, that has two end seals, and the gauge block and reg had flat sealing surfaces, you could vent that way.

A regulated, 40FPE 22 cal Mrod is certainly achievable. The question will be at what shot count.

I think 40FPE will require spring changes in bolt for cycling, but not 100% sure.

I still have a few Libertys, the predasessor to the Avenger. Externally adjustable regulator is nice and can somewhat compensate with higher fills. I believe the plenum is only 5cc, and not easy to make larger. I wish Nova Vista would sell parts.


 
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Ok thanks! That saved another assembly and tear down. Orings arrived, got everything back together. In the future will push everything down from the fill end of the tube. Using the shorter path from the back means pushing across a number of sharp of holes through the tube that want to take little bite out of the Orings. Filled up to 3000 psi with no problems I could see. 

I need to temper my expectations about the power and reliability trade off. Really appreciate the guidance keeping this on track and reversible! 

Will check back in tomorrow when I know if it is holding air to start testing. 






 
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Yea, you only do that once. ;) I use a wooden dowl rod or plastic pipe to push the parts individually down the tube. Heavily silicone grease each O-ring to get past the threads. I clean and silicone oil the inside of the tube, too. I also mark the end of each with some black marker, because they will sometimes spin in the tube. When they get to the gauge hole, they may need re-orienting.
 
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