Modding/Tuning A .22 MRod for max vel/power with CO2?

Modding/Tuning A .22 MRod for max vel/power with CO2?

Joined: October 31st, 2007, 8:36 am

April 12th, 2012, 3:50 am #1

I'm planning on getting a .22 Marauder to run exclusively on CO2.

I have many CO2 guns and no PCP's. And CO2 is much more available where I live. I know an MRod on CO2 will never compete with one on compressed air. But I'd like to mod/tune to get as much velocity/power as possible and then mod/tune for best accuracy and shot count at that power.

Would I benefit from installing the higher flow valve body and transfer port from the .25 MRod in a .22 run on CO2?

Would adding the HDD from AoA help with shot count without hurting velocity?

Is there anything else that would benefit me in this pursuit?
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Joined: July 9th, 2004, 6:53 pm

April 16th, 2012, 9:03 pm #2

Open the valve adj screw 4 turns out from bottom. Bore the transfer port to .125 inch. Back both hex adjust screws all the way out and use just the bigger .25 inch (?) to increase striker spring tension until velocity hits max. Any more than that will release so much CO2 and chill down the volume and reduce velocity. Increase until the velocity drops. Do this with a heavy pellet to get all the push available. The HDD will only make performance better. Mine is getting 525 fps with a Kokiak (21.1gr) at 68 degrees.
Last edited by SirTonySteel on April 16th, 2012, 9:06 pm, edited 1 time in total.
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Joined: October 31st, 2007, 8:36 am

April 19th, 2012, 5:41 pm #3

Thank you for the advice on adjustments for CO2.

I have read that the factory .177 and .22 transfer port is .120. Instead of reaming to .125, do you think substituting the .140 transfer port of the .25 M-Rod, along with substituting the higher flow valve of the .25 would help?

I'll definitely go for an HDD.

I'd like to see if I could get to 600fps or more with 18gr+/- pellets.

I've been reading here about the highly variable barrel quality of the .22 M-Rods. Is this issue still on going or did Crosman finally address it?
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