Simple tune for Gen 2 .25 cal. Marauder Rifle

[hill]

"What is a good and simple tune for a stock Gen 2 Marauder Rifle, especially for someone that does not have access to a chronograph".

This question comes up from time to time, so since I have a stock rifle, I thought I'd post an example tune.

The test rifle:
My stock { except for the barrel band, flashlight, scope, and rings - nothing that would alter the power plant from stock } Gen 2 .25 cal. Marauder Rifle.

Specifications:
Fill pressure 3000 psi ( use an accurate gauge )
Velocity Screw ( 5/64” wrench ) = turn CW until stops, then 5.5 turns CCW ( don’t forget to remove the set screw first )
Hammer Throw ( 1/8” wrench ) = turn CCW until stops
Hammer Spring ( 1/4” wrench ) = turn CCW until stops, then 3.5 turns CW

In my rifle ( yours may vary slightly ), when shooting a 25.39 grain pellet, I get 24 shots from 810 - 840 - 810 fps ( 37 - 40 foot pounds of energy ). That is an extreme
spread in velocity of 30 fps or 3.6 %.

If you want a little more power, and with a lower E. S., but at the expense of a few less shots per fill, you can set the hammer spring preload adjustment to 4.5

[Wyldman]

Thank you, Mr. Hill, for a simply stated and easy to understand starting point. Something that, so far, has seemingly been some arcane secret. This info will go a long way toward making tuning of these rifles much easier to understand and implement, not to mention giving a good baseline to return to should tuning efforts go awry.

Well done, sir! Heartfelt thanks again!

[hill]

Thank you, Mr. Hill, for a simply stated and easy to understand starting point. Something that, so far, has seemingly been some arcane secret. This info will go a long way toward making tuning of these rifles much easier to understand and implement, not to mention giving a good baseline to return to should tuning efforts go awry.

Well done, sir! Heartfelt thanks again!

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Thank you, my pleasure to be of any assistance.

Hopefully after today, this month, etc., this post will remain easy to be found - for those in need of a simple starting point

[Hummerbk]

Thanks Mr. Hill,

I set mine up as you suggested. I ordered a depinger and a Mcmaster Carr pressure gauge as mine pegged out. I'm not looking forward to pumping from zero psi. My velocity screw was only 2 1/2 turns out.

Mine is a gen 1 so I hope the starter tune you posted will work as well on it.

[RayK]

Mine is a gen 1 so I hope the starter tune you posted will work as well on it.

No, it won't be the same on a Gen I which has a lighter valve spring than the Gen II.

You should try the Improved BLT which is VMS 5, HT 6, and HS 3 which will give you 24 good shots within 3% from a 2500 psi fill shooting JSB Kings at a peak of 790 FPS.

Ray

[hill]

Thanks Mr. Hill,

I set mine up as you suggested. I ordered a depinger and a Mcmaster Carr pressure gauge as mine pegged out. I'm not looking forward to pumping from zero psi. My velocity screw was only 2 1/2 turns out.

Mine is a gen 1 so I hope the starter tune you posted will work as well on it.

- - - -


For your Gen 1 rifle to shoot at/near this same level of power, ( along with the other stated adjustments ) you may want to add a turn or two ( CW ) to the hammer spring adjustment.

[coenen]

I have my GEN 1 at;
HT 6
HS 6
vms all open.

But iff i fill it to more than 3000psi(200bar) it is not shooting correct...

[RayK]

I have my GEN 1 at;
HT 6
HS 6
vms all open.

But iff i fill it to more than 3000psi(200bar) it is not shooting correct...

In a Gen I, that should give you 24 good shots from a 3000 psi fill at a peak of about 830 fps with JSB Kings.

Ray

[caniborrowsomeammo]

Meaning of "correct"?

[coenen]

correct= i mean, pellets al over the place, to high and left and right from the target... ones i get to 3000 psi i can shoot nice groups...