P-Rod…Poly tube exchange for the OEM transfer port…
Problem: The OEM transfer port on the P-rod has a tiny inside diameter. Further, the tube and barrel also have a tiny port for the air to pass through.
Solution 1: Remove the transfer port and replace it with 1/4″ poly tube and drill out the tube and barrel ports.
Results: FPS in the early 700’s with 18gr pellets, but a 16 shot capacity.
Solution 2: Remove the transfer port, leave the tube and barrel ports at OEM size, and put in a 1/4″ poly tube.
Results: FPS still in the early 700’s, with 14gr pellets, but no loss in shot count. Figure 24 shots, or three mags.
Solution 2 has two ways to do it, and both apparently work. One removes the two flat black washers in the tube and breech ports and the poly tube connects the two ports. The other way is to leave these soft black washers in place and use a shorter poly tube and allow the washers to seal the ends of the poly tube at the breech and tube ports. Both ways seem to work with no air loss. That being the case, I’d use the poly tube without the flat washers in the ports next time. Easier to work with.
Here’s a pictoral sequence of what I did…..
Remove the four hex bolts at the top of the breech.
Between the breech and the tube, there are only two pieces that connect the two. One is the trigger/hammer pin, and the other is the transfer port. Only the transfer port is removable at this stage.
The transfer port consists of three parts. One washer in the breech, one washer in the tube, and one plastic (blue) transfer port that fits between the two washers. The transfer port easily pulls out, but the black washers need to be pried out with a pick.
Breech with washer still installed.
Tube with washer removed. (note how tiny the port hole is compared to the washer diameter)
If you do as I did, leave the two compression washers in the breech and tube, then measure how long the transfer port is.
Then use a razor or hobby knife and cut the poly tube as close to that measurement as possible.
Replace the two washers back into the breech and tube ports, and put the poly tube into the breech because it has the deepest recess to hold it in place. Then join the two parts carefully.
Then carefully put the breech on top of the tube. In this picture, the hammer pin is being aligned for insertion into its slot, as I slowly move the tube port/washer over to the breech poly tube seen to the left. Slow is good at this point. Press them together. Note that while the poly tube is partially recessed in the breech even though the washer is in place under it, it will fit surface flush against the washer in the tube. Slow and careful alignment is the key, as the washer will compress in the tube as you close the two together.
After closed, hold the breech and tube together with your thumb and forefinger and replace the four screws, being careful to tighten them in a staggered manner ie: 1, 3, 2, 4, do not over tighten them. Take them to where they stop and then a quarter turn, no more.
And that is how easy it is. The hardest part was cutting the tubing to the exact length required to replace the missing blue transfer port.
When I get everything back together, I will post my chrony results. I have a spare barrel/tube band coming from Crosman this week and I’m still finishing up some efforts on the stock.
I hope to have pics and results posted by mid to end of this week. If my results mirror the earlier posts results, it would be silly not to undertake this ultra simple modification. Drilling the breech and tube ports does not seem to be worth the effort. Adding a 1/4″ washer behind the hammer spring may or may not assist results…that is not known at this time, as the guy who did it also did the poly tube mod at the same time.
Stay tuned. I have some ideas on mods for the shroud to get the sound down to managable levels. With the poly tube installed it was obvious more air was coming out the muzzle and the report was unacceptably loud for my cop calling neighbors. Still, it wasn’t all that bad for a shroud with no baffles in it, as the Mrod has.
Regards,
Hoot
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Great write up 😀
Do you think your second method would apply to the as2250? The next mod on my list is the poly tube mod but I would like to keep as much oem as possible. Your results show its just as good to replace the transfer tube than to go the whole hog and drill out the valve and barrel port, is this how you see it also?
:thumb:
test
My next effort will be to quiet this sucker down a bit.
It’s great to get 700+ fps out of this little beast, but it does get louder.
My first consideration is to do the Eduard trick and drill a few tiny holes at the back of the shroud to relieve air pressure, and I do mean “tiny”. Probably 1/64″ and I’ll start out with four equally spaced holes.
Another idea is to move the air stripper up a notch so that two of the air hole sets, in the barrel tip, release air to the back of the shroud instead of into the relatively small space left in the front of the shroud. As there are no “baffles” in the shroud, it leaves little to work with, unless you get a longer shroud and pop a few Marauder cup baffles into the mix. That adds length and I’d like to keep this as short as possible.
Perhaps some of the shroud people might suggest an air movement friendly “wrap” to wrap around the barrel at the back to help muffle and slow the air release in my new rear relief holes??? I’m thinking SS mesh or scouring pad material. Some fairly stiff plastic material might do as well, if I can find the right weave or porous material. And/Or, possible a metal washer (with four to six air holes in it) drilled to the barrel OD, and filed to the shroud ID diameter, and placed 1/2 way back in the shroud to slow the movement of air to the rear relief holes. A little JB weld would hold it in place and this would create two baffled compartments instead of one, for the air pressure to push through.
I think the main idea is to reduce as much of the air being forced out the front of the shroud as possible to reduce “blast”. Right now, the majority of the air pressure is being relieved at the muzzle end of the shroud, and that has to change.
More later…..
Kindly, but ignorant, ‘Ol Uncle Hoot 😯
Breaking laws by shooting air guns isn’t necessarily illegal…getting caught doing it, by people with different perspectives, appears to me to be the greater problem.”
Excellent report Hoot .
When I did mine I drilled out the transfer port to a larger diameter , achives about the same thing . With the spacer on the hammer spring I get 700+ fps with 18g JSBs for about 16 shots .
Looking forward to hearing more results . For the price this is a great pistol and a lot of fun to play around with .
Great report.
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i tried the poly tube replacement,with hammer spring in 5 1/2 turns,travel in 2 turns,without tube average vel. was 665 fps, with poly tube shot string was 1- 684 2- 712 3-721 4-725 5- 735 6- 744 7- 743 8- 752 9 -758 10- 760 11- 762 12- 760 13- 761 14- 753 16- 751 17- 748 18- 739 19- 733 20- 726 21- 717 22- 713 23- 707 24- 696 fill pressure from 3000 down to 1200 ,i have a swift extended chamber with insert and majic eraser material inside chamber under vent holes, its very quiet and very accurate,really great pistol.cp,14,3 pellets