P-Rod velocity question

P-Rod velocity question

Joined: April 3rd, 2008, 10:15 am

April 13th, 2012, 11:48 pm #1

I have a P-Rod with a Gaska Butt adapter to make the gun an adjustable stock carbine.
The gun has never been changed from factory settings and I am getting aprox 630 - 650fps using Crosman Premier 14.3gn pellets. I ca get 4 magazines or 32 shots with it dropping down to 602fps

My "Goal" (if possible), is to shoot 18.1gn pellets @ 700fps and get 3 magazines instead of 4 magazines, such as- (24 shots @ 700fps instead of 630 - 650fps for 32 shots.

Has anyone done this before without any major modifications?
Which way and how many turns for each Allen bolt adjuster?

All advise is appreciated:)
Thank you!!
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Joined: November 17th, 2006, 3:51 am

April 14th, 2012, 12:20 am #2

..I think you might be able to.
From your numbers, the high reading is 650 and the low is 602...call it 48fps change over the string you counted. IF you give the same vel.variation to a higher speed string (700-652fps) you might be able to get the PRod to do it,

IF it were me, and i wanted that kind if speed, would:
1. Crank the spring tension all the way back (lefty) from the factory setting and then crank it in (righty) 7 turns.
2. Crank the dwell to the left until it stops (maximize stroke).
3. Fill to 2900-3000psi
3, Chronograph it,


IF (and I hope this is true for yours) its a little fast, would make a new transfer port a tiny bit smaller. Keep farting around with transfer port size until it go to the area in which you want it to shoot peaking at 700fps)...then chronograph a string.

Might find (as i suspect) that you can get that speed,. but more likely to see 2 to 2
1/2 mags worth of shots before it climbed up from 650 to 700 and then fell back down to 650.
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Joined: April 3rd, 2008, 10:15 am

April 16th, 2012, 12:32 am #3

Thank you for your post and information:)
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Joined: July 13th, 2009, 2:26 am

April 24th, 2012, 11:27 pm #4

I have a P-Rod with a Gaska Butt adapter to make the gun an adjustable stock carbine.
The gun has never been changed from factory settings and I am getting aprox 630 - 650fps using Crosman Premier 14.3gn pellets. I ca get 4 magazines or 32 shots with it dropping down to 602fps

My "Goal" (if possible), is to shoot 18.1gn pellets @ 700fps and get 3 magazines instead of 4 magazines, such as- (24 shots @ 700fps instead of 630 - 650fps for 32 shots.

Has anyone done this before without any major modifications?
Which way and how many turns for each Allen bolt adjuster?

All advise is appreciated:)
Thank you!!
The two simplest modifications to bring your fps up to 700+ is to do the following:

1) Drill out the transfer port to .118


2) Get a GMAC 22XX Heavy duty spring and replace the OEM hammer spring with it.

3) Having done this, you can then play with the hammer spring throw and tension if you want. Just be sure to
note the factory settings so you can return to their original settings if you get lost doing all that turning
and changing sizes of Allen wrenches.

No other adjustments should be needed. I've done this three times and it worked
every time. The transfer port is four bolts away and easy to do with a hand drill.

The GMAC spring is ordered on-line and costs about $15.00 shipped.

Have fun.

Hepotter
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Joined: April 3rd, 2008, 10:15 am

April 24th, 2012, 11:52 pm #5

Thank you for your post.
A couple of questions-
What size drill is a .118 in fractions? like a 1/16? 3/32? etc??

Where do I get a GMAC 22XX Heavy duty spring and what is the cost of the spring?
What is the cost of shipping?
Anything else I would need?

Basically, you are saying just a larger transfer port would do it (700fps using 18.1gn pellets)
Do I need a bench drill to make a "perfect" hole?

Let me know if I got this right-
Make the port .118 and where it is factory set should jump up to 700fps? (adjust if needed)

How many shots do you get with your gun and .118 port?
What pellet weight do you use?
What is the velocity?

Thank you very much, sounds like a plan:)
PS, any video's, etc of how to take this apart, etc? If you do not know, I will do a search..., just thought if you had a link to one, it would be a big tome saver:)

Thanks again for your information and help!!!
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Joined: July 13th, 2009, 2:26 am

April 28th, 2012, 11:57 pm #6

Here is the web site for the GMAC spring. Just toss the brass rod and exchange the Crosman spring with the new GMAC spring. About $15 USD total.
http://www.gmaccustomparts.com/epages/B ... ts/0GCPHS1

The exact size of the drill bit is not critical, as long as it is larger than the diameter of the existing transfer port hole. You can't get it too large, as the valve port controls the amount of air released. All you are doing is giving that amount of air an open pathway to reach the rear of the pellet. A perfect hole is not needed. I used a AA battery powered hand drill and held the transfer port in my fingers while I drilled it. Further, the barrel port, just above the transfer port, can be drilled out with the same drill bit used on the transfer port. That way max air quickly gets to the pellet from the valve.

Some hammer spring throw and tension adjustment may be needed. Just check the A team's post on adjustments, or check Youtube for several posts on adjusting these two items.

Google an exploded view of the Prod, and you will see the four bolts holding the breech on top of the transfer port. The spring is also quite simple to get out and replace, just look over the exploded view carefully to see what screws to remove.

I used 18.1 grain JSB, which I believe are the best pellets available for the money. My velocities were 750+ fps with this pellet. An amazing increase with such a simple modification.

I was getting three magazines of eight shots with the mods. Plenty of power. Stupid simple.

I got a Jim Gaska butt stock adapter and a collapsing stock from Tipman, each was about $30.00 and made a dandy folding carbine. Jim also has a shroud extension to quiet down the noise to near nothing.

Have fun. Go slow. Enjoy. Let us know how you do.


Regards,
H. E. Potter


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Joined: April 3rd, 2008, 10:15 am

April 29th, 2012, 9:03 pm #7

Much Appreciated!!!
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