Author Topic: Huma regulator for my Gamo Urban .22  (Read 1502 times)

10 Acre Woodsman

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Huma regulator for my Gamo Urban .22
« on: January 28, 2018, 10:46:21 AM »
Hello Bob,
I have been going through a lot of your posts concerning the specifics of regulators. I have ordered a Huma regulator for my Gamo Urban .22. But instead of ordering the reg for a .22 caliber rifle with the smaller plenum, I ordered one for the .25 cal with a larger (longer) plenum. I have a chronograph lined up to use this week to compare before and after results. I have not found any videos of Huma regulator installations into an Urban, Coyote, or BSA Buccaneer. My first question is this, will I most probably need to reduce my hammer spring tension to accommodate this regulator? Second, is there a ballpark psi (bar) to start with? Third, can I safely raise my fill pressure with this regulator installed, say to 250 bar to get a few more shots? Also are there any readers here that has done this particular install? Thanks a million, Troy

105cc fill tube
Max fill pressure 232 bar. I usually fill to 206 bar because I have a 3000 PSI fill tank.
Getting around 20-25 shots with 14.3 grain Crossman Premier Hollow Points before it falls of the reg.
Accuracy is awesome, can put 10 shots almost in same hole while in the sweet spot at 25 yards.


  • Soddy Daisy, TN

Alan

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Re: Huma regulator for my Gamo Urban .22
« Reply #1 on: January 28, 2018, 11:09:01 AM »
The Gamo isn't an expensive PCP, but with a few mods (you're already in the middle of one), they're decent shooters. It will be interesting what Bob (airgun hero) has to say.
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Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.

rsterne

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Re: Huma regulator for my Gamo Urban .22
« Reply #2 on: January 28, 2018, 11:16:03 AM »
Yes, you will need less hammer strike, because you no longer need the hammer to open the valve at 206 bar....

To determine your setpoint, shoot a string and record the velocity and pressure along the way.... If your string is, say, 900-950-900, from 206 bar down to 120.... and you want to shoot 920 fps.... look at what the pressure is on the second half of the string at that velocity.... Let's say it is 140 bar, then that would be the theoretical setpoint for your regulator.... If you are happy with 900 fps, then you should be able to use 120 bar....

The caveat is that if the plenum is less than about 1 cc per FPE, you will have to increase the setpoint pressure to compensate for the pressure drop during the shot.... How much will depend on how the gun breathes in it's unregulated state.... If the reservoir is wide open to feed the valve, then you have all 105 cc available now to prevent pressure drop during the shot.... If you end up with only a 10 cc plenum, you will get 10 times the pressure drop during the shot, which may mean you don't get the FPE you are expecting to.... You must compensate by increasing the setpoint pressure....

I can't comment about overfilling your gun, as I know nothing about it.... but in general it is not a good idea....

Bob
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10 Acre Woodsman

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Re: Huma regulator for my Gamo Urban .22
« Reply #3 on: January 28, 2018, 12:39:27 PM »
Thank you Bob! :-)
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sjames13

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Re: Huma regulator for my Gamo Urban .22
« Reply #4 on: March 24, 2018, 07:05:11 AM »
Do you  have a recommended hammer spring OR recommended spring "pull force"?

I ordered a Gamo Coyote Huma regulator, set the pressure at 130 bar, and then installed the regulator in my air rifle.

Prior to installing the regulator, the Coyote averaged about 30-35 shots at approximately 935fps using 14.3 grain pellet (roughly 350 total shots).  Initial fill usually about 3200psi fill, and each shot averaged about 40-45psi, ending in about 1850psi before a significant drop in muzzle velocity.

After installing the regulator (set at 130 bar), the Coyote averaged about 15 shots (about 57% drop -- bad) at approximately 910fps (about 2.8% drop -- acceptable) using 14.3 grain pellet, with each shot averaging about 100psi (bad).  I think the hammer is hitting the air transfer valve pin with too much force.

Aside from the pressure regulator, power adjustments are via the diameter of the air transfer port -- there is NO hammer spring adjustment capability in the Coyote.  I am ok with the current power, but need to improve the air usage ... preferably bring it back to about 40psi per shot.  I understand this can be done by changing the hammer spring and/or hammer.

Can you recommend a replacement hammer spring, one that is "lighter"?  The original hammer spring seems to be about 21 pounds of pull pressure.

Thank you!

rsterne

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Re: Huma regulator for my Gamo Urban .22
« Reply #5 on: March 24, 2018, 09:52:17 AM »
Sorry, I am not familiar with the Coyote.... but when you installed the regulator your hammer spring became too strong for the job, so you are correct in looking for a lighter one.... There are lots of springs available from companies such as Century Spring or even McMaster-Carr, it is a matter of finding some that are the same diameter and length but made from smaller wire.... There is an alternative that may also work well, particularly if you can get a spare Coyote spring as a backup....

If your velocity is too low, then increase your setpoint pressure a bit until it is a bit higher than you would like.... It is normal to get a lower velocity when regulated as the peak when unregulated (because the pressure is lower), so don't expect too much.... Shorten your existing spring a coil at a time, and check the velocity each time (just a shot or two, you don't need to shoot a whole string).... When the velocity starts to drop, then start cutting only about 1/4 turn at a time until the velocity is 3-5% below the plateau (maximum) veloicity.... That should give you the best balance between power and efficiency at the setpoint pressure you are using.... If you plot a graph of velocity vs. preload you will get something like this....



The ideal tune on that gun is at about 5 turns out from coil-bind on the spring.... but you might end up using between 4.5 - 5.5 depending on your results.... You would be shortening the spring, and if you go too far, you can shim it back up, or replace it with your backup spring, cut slightly longer.... One other thing.... do NOT worry if you end up with no preload on the spring and it actually rattles around between the hammer and rear spring seat when the gun is not cocked.... That is what we call an "SSS" (short stiff spring) and is effective at eliminating hammer bounce, which conserves air....

Bob

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GamoUrban153

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Re: Huma regulator for my Gamo Urban .22
« Reply #6 on: May 19, 2018, 08:30:04 AM »
Hello.  In case you have not discovered it yet, here is a hammer-spring adjustment.

Remove the stock.  Then remove the black plastic rear end-cap that slides in under the rear of the bolt.  That end-cap covers a hole that goes into the trigger-group.  Inside of that hole is a 4mm hex head hammer-spring adjustment screw.  It is approximately a 15 turn adjustment from one extreme to the other.  Turn it fully counterclockwise to the stop and it has the least tension (lowest power).  Turn it 15 turns clockwise from that and you have the most tension and highest power from that adjustment. The cocking effort of the bolt is determined by this adjustment also.  The more clockwise the more effort it requires.  Any much further that 15 turns clockwise will make it physically impossible for the gun to cock.  With my gun anything over 10 turns CW from full CCW was more of a waste of air than a gain in power.  For the most shots and I found 6 turns CW to do the trick, although it it drops the power from about 24 fpe to 20 fpe.  I am currently waiting for my new chronograph to come in to test 6.25 and 6.5 turns CW to see if I can get consistent 50 shot strings of 21.5 fpe with JSB 18.13’s which seen to be more efficient with my gun than the H&N 17.9 g Sniper Magnums.

I fitted a Robert Lane Lancet MK9 regulator to the gun, set at 120 bar...  that may change again...  I tested from 70-120 and I am going to play around with 100 through 115 again after I experiment with different transfer port diameters.  Also a shot count of 60 at approximately 20 fpe is possible with less than a 20 fps spread (with 17.9’s, the 18.13’s should do a little better).  This is partly possible because also I replaced my Urban 105 cc cylinder with the 153 cc Buccaneer/Coyote cylinder to make up for the space occupied by the MK9.
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