P-Rod Build

[Jzizzle]

I recently picked up a marauder pistol.  Plan is to add a bottle and butt stock for a carbine style hunter/plinker.  High shot count and power is what I want here.

In stock form out of the box Jsb 18.13 moving at 580-600 fps.  With hammer adjustment max was 622fps. Shot count not so good with a declining string.

1st round of mods:
- Barrel ported to .140
- Magnum TP .140
- Valve ported to .140
- Hill Valve Cap
- Hill 45 Hammer Spring
- Hill Peek Hammer Striker
- Hill Gauge Port
- McMaster Extreme Pressure Fittings (5000psi)
- 350cc Carbon Fiber Bottle
-2400psi Regulator
-Magnum Trigger
- AR buttstock
- Donny Sumo LDC

Jsb 18.13 moving at 800 fps for 26fpe
Jsb 33.95 moving at 650fps for 32fpe

In the process of printing a bottle brace with a bottom rail for a bipod.

I had originally planned to cut the OEM tube and use a jds bottle adapter, but opted to go this route for a huge plenum. 

Plenum is around 65cc+350cc bottle.

While I'm limited on power with a 12" barrel, there's gotta be more to extract from the prod.

After the porting and prior to bottle/reg, I was achieving 880fps with Jsb 18.13 and 700fps with Jsb 33.95. So I lossed 50-80 fps with the reg.   

Perhaps open the ports up a bit more and if needed raise regulator.  Is 40-45fpe possible?

I'll do a full string hopefully tomorrow and see what the shot count and efficiency is at with the present tune.

[Jzizzle]

Well the pictures won't attach.

The bottle is attached at the gauge port.  Also using an asa for easy removal.

[Tucobenedicto]

With the original 12" barrell i think you can (maybe) reach 40 fpe raising the regulator setting around 3000psi,it can worth if you can fill at 4500psi,but shot count goes out of the window.
About porting,you can open up to .165 without issues.

[Jzizzle]

With a bottle fill of 4000psi - 2000psi I get 105 shots with Jsb 33.95 at 650fps.  Efficiency of .96

One thing I'm not a fan of is the rear cocking bolt.  Maybe take a look at the eBay side lever breech.

Regards to further porting, I probably will do this..see if I can speed up the 33.95 around 770fps.

[Jzizzle]

Disregard that shot count, gauge showed 2000 but was actually 2600 on compressor.

I'll have to redo. Got a 5k Talon Tunes gauge on the way

Accuracy wise, tested at 25 yards and 70 yards with Jsb Hades 15gr, 18gr and 34gr.
All did excellent at 25 yards.

At 70 yards the 18gr were best, followed by hades, then 34gr beasts.  Beasts need more speed at this distance.

Hades 825fps
18.13 800fps
33.95 650fps

[Jzizzle]

I opened up the barrel/valve port to .171 (11/64) and TP to .156 (5/32).  Not enough material to take it one more step up.  Testing now unregulated with hammer spring adjusted max power is around 2600psi.  Whats interesting is I only gained 10fps over previous testing with .140 ports while being unregulated.  18.13 max at 890fps for 32fpe.  I didn't try the 33.95 today but will for sure when the reg goes back on.

I have a new bottle reg on the way so final tuning to follow. 

[Tucobenedicto]

Just for reference,my Prod before barrell swap was at 794fps with 18,1 JSB's ,all ported at .165 and regulator setted slightly over 2000psi.
I opened a bit the valve throath (under the poppett) and smoothed the internal edges of the valve port with a tiny ball shaped dremel bit to improve the flow.I keep the trow adjustement to max trow and tune by preload only.

[Jzizzle]

What length barrel are you using? And how much gain did it give you?

 Im definitely keeping oem barrel for this carbine build.  I think a realistic goal on the top end is 40fpe.

More to come...

[moorepower]

Have you opened up the valve throat yet? That may be your restriction at this point.

[Jzizzle]

I think your exactly right!  Valve throat will be opened up next.   

.265 (17/64) seems to be the max I can go here?

[Tucobenedicto]

What length barrel are you using? And how much gain did it give you?
Now the barrell is 16,5",same pressure as before (2000psi),i gained 5FPE,keeping the tuning 5-7% under the peak speed.

 Im definitely keeping oem barrel for this carbine build.  I think a realistic goal on the top end is 40fpe.

More to come...

[Tucobenedicto]

I think your exactly right!  Valve throat will be opened up next.   

.265 (17/64) seems to be the max I can go here?

Don't remember the drill bit i used,the sealing surface in the valve is a protruding "ring",be sure to keep this almost untouched or the poppett won't seal anymore.
If you can access to a lathe and the proper tool,you can enlarge a bit the valve internal around the poppett too,(but i skipped this part in my valve).

[FuzzyGrub]

I think your exactly right!  Valve throat will be opened up next.   

.265 (17/64) seems to be the max I can go here?

I don't remember what the max is, but that is way past it.  I think it is stock around 0.20", and can go to 0.22", maybe 0.23", without tearing into seat.  You can get a little more out of the poppet stem. 

It is very easy to nick and ruin the valve seat or go too far with the drill.  I incrementally step through number drills, turning the drill chuck by hand.  Crosman does sell the valve body separate, in case you go to far. 

[Jzizzle]

Ok I'll get some measurements when I open it back up.  And follow up with chrony numbers.

In addition to 18.13 and 33.95, I have some 25. Redesign coming to try out too.

[FuzzyGrub]

FWIW: On a more recent build, used 0.160" poly TP, exhaust and Barrel port to 0.160", was getting right around 30fpe, but that was with an O-ring buffer to try to limit over-dwell using a 10" barrel.   I think the stock pocket area is a hair less than 0.160".

I think you will need to open things up to 0.180" for 40fpe.  Also look at the bolt probe.  I don't recall the OD, but its on the fat side, and might not meet the 0.180 flow. 

[Jzizzle]

Appreciate your input.  Let's see what gains come from opening the throat first. 

At its current state, we already achieved 37fpe unregulated and 32fpe regulated at 2400psi with the jsb 33.95gr.

[FuzzyGrub]

Appreciate your input.  Let's see what gains come from opening the throat first. 

At its current state, we already achieved 37fpe unregulated and 32fpe regulated at 2400psi with the jsb 33.95gr.

I only have used up to the 25g pellets.  If I understand your build correctly, your plenum is basically the whole air tube. 

BTW, you are overdue on pictures.   

[PikeP]

Is there more left? Yes, tons. My spreadsheet is currently predicting your valves performance within 1%.

With 90% bore porting...you will go from (with .14 ports) 800 fps on the 18.13, to 950 fps. So to say there is a bit more, is an understatement, there is a LOT more left...your porting is severely limiting you.

Shooting the 33.95's should put it at 36 fpe.

Want to hit 40's? Well, go full bore. That right there, will put you right on the nose for 40 fpe...or

Run 90% bore porting and 2650 psi..

[Jzizzle]

Appreciate your input.  Let's see what gains come from opening the throat first. 

At its current state, we already achieved 37fpe unregulated and 32fpe regulated at 2400psi with the jsb 33.95gr.

I only have used up to the 25g pellets.  If I understand your build correctly, your plenum is basically the whole air tube. 

BTW, you are overdue on pictures. 

Yes the entire oem reservoir is the plenum.
If you can lend a hand in uploading a picture. I simply snap a pic on cell phone and attempt to attach but says file is too large.

[Jzizzle]

Is there more left? Yes, tons. My spreadsheet is currently predicting your valves performance within 1%.

With 90% bore porting...you will go from (with .14 ports) 800 fps on the 18.13, to 950 fps. So to say there is a bit more, is an understatement, there is a LOT more left...your porting is severely limiting you.

Shooting the 33.95's should put it at 36 fpe.

Want to hit 40's? Well, go full bore. That right there, will put you right on the nose for 40 fpe...or

Run 90% bore porting and 2650 psi..

I will raise the output pressure, got 2 different regs on order.  I was gonna go with jsar adjustable one but have my reasons for not going that route.

I'll take this one step at a time recording improvments and hopefully we can hit 40-45fpe.