Tuning Pitbull / huma regulator on modified benjamin bulldog update

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bd2021

bd2021

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Nov 18, 2021
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MN, United States
ReL old thread here: https://www.airgunnation.com/topic/is-this-normal-for-a-huma-regulator/?referrer=1

So, I guess what Pitbull airguns meant by "special tool" to adjust the Huma regulator is shown here in this video/timestamp:

https://youtu.be/Y_AvdD9YTGk?t=460

It looks like they set the regulated pressure using this gauge and a screwdriver, and don't rely on the printing on the side of the regulator. Seems reasonable, and they are correct...I don't have such a gauge. 

By the way, with my chronograph and 135 grain griffin LDC Boat tail slugs. I am getting about 905 fps/247 ft.lbs of energy.

The custom pitbull does seem to be an air hog (especially with a hand pump and 4 regulated shots from 4500 psi) but that is a lot of energy...so this may be reasonable? 

Any thoughts from those more experienced?
 
4 shots? Their web sight says 11 regulated. This grabbed my attention because I have the extended tube and regulator on the way and was planning on getting at least 10 shots per fill. I don't have the valve and barrel ported to the same sizes that they port though. All I'm looking to get is around 200fpe and good accuracy from the regulated pressures.



You could try backing the hammer spring out a turn or two and see what happens, if power doesn't go down, it might at least use less air. Or power decreases.
 
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> You could try backing the hammer spring out a turn or two and see what happens, if power doesn't go down, it might at least use less air. Or power decreases.



Thanks for the tip. I'll try that tonight. They did respond to email yesterday asking me to return the gun for inspection and repair. I'm going to call anyway because I don't want to waste their time. I am a newb. If it needs repair I'll send it in...that would be great, I like dealing with American companies that stand behind their product. I know from other forums in completely different hobbies that sometimes small businesses get but hurt if anybody unfairly criticizes them, and I am doing my best to not unfairly criticize them. We all need to make a living, and I prefer to keep my earnings in the U.S. circulating with other American businesses when possible.
 
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So far every time I've dealt with them, they have been good. Responses are generally short and to the point, but fairly accurate. And they at least took their "proprietary" knowledge and put most of it out on the web, granted much of that knowledge can be found by searching here about 6-8 years ago, but they compiled it and presented it. By now I have almost another BD worth of parts from them, so really can't complain too much. Hoping the reg and bigger tube will do what I want, because I'm not really getting there with stock size parts. I can get like one or two shots up where I want to be, but then the pressure falls off and soon out of air. Bigger tube and reg should do what I need, even if it is no longer hand pump friendly. 

A bottle Bulldog might also fix the issues I'm having, wouldn't need a regulator for that type of set up and wouldn't need 4500psi either. Still not fun to hand pump, like my Kral Empire X with the 500cc bottle, I tested pumping and gave up fast. Pumping can't get the valves closed either, need a compressor and fooling around, or a tank to blast it closed.

My other rifle (that has been back for warranty work twice) has a lot more power, a lot more volume of air, and definitely not friendly to hand pump. if I was survival hunting for food with it, I could probably pump the one or two shots before bed, but it would take a bunch of time. This rifle gets 3 shots regulated, with a 4th of enough power to finish a job, the fifth shot purges the air system and then you are screwed for hand pump. Instructions say you can not pump fast enough to get all the valves to close, so it might be an issue in a survival situation.
 
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So I was able to test it, after talking to pitbull. I tightened the hammer spring, then unenlightened it 3 full turns. With an initial 4500 psi in the modified pitbull, I got:

Shot count: First 5
Low: 907 fps (919 fps for first 4)
Hi: 939 fps (939 fps for first 4)
Avg: 923 fps (927 fps for first 4)
STD Dev: 10.8 (7.9 for first 4)
Spread: 32.0 fps (20 fps for first 4)


3/23/22 12:35:47 PM, 939 fps 264.7 ft. lbs
3/23/22 12:36:10 PM, 921 fps 254.3 ft. lbs
3/23/22 12:36:35 PM, 930 fps 259.5 ft. lbs
3/23/22 12:37:02 PM, 919 fps 253.0 ft. lbs
3/23/22 12:37:38 PM, 907 fps 246.7 ft. lbs ** plenum below regulator **

I am not sure if this is good or bad. This was into a pellet trap so I haven't checked long range accuracy. 

The spread is larger than on my crown MKII, but that is only .25 cal.
 
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I have a pitbull as well. Extended tube, 4500 psi, regulated at 2900 psi, ported and polished by me. Get 12 full on power shots. 

142 gr NSA

shot 1 898 fps / 254 fpe

shot 2 907 fps / 259 fpe

shot 3 877 fps / 242 fpe

shot 4 881 fps / 244 fpe

shot 5 879 fps / 243.fpe

shot 6 896 fps / 253 fpe

shot 7 901 fps / 256 fpe

shot 8 891 fps / 250 fpe

Standard Deviation is 11.15, spread of 30. Has gone as low as Standard Dev of 4.68 and spread of 20.

So on and so forth to 12, then it falls off the regulator. Hammer spring is 3 turns out from all the way in.

-JP
 
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My stuff arrived today, but haven't had a chance to really look at it yet. I need to make a mod to the barrel before I put it on too, so not entirely certain when I'll get this done.



Also fighting with Umarex over a warranty issue on a different rifle, really not happy when someone calls me and tells me that with the decades of experience, the problem I have video showing doesn't exist to their gunsmiths. Which ultimately means they didn't really look at it.
 
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I have a pitbull as well. Extended tube, 4500 psi, regulated at 2900 psi, ported and polished by me. Get 12 full on power shots. 

142 gr NSA

shot 1 898 fps / 254 fpe

shot 2 907 fps / 259 fpe

shot 3 877 fps / 242 fpe

shot 4 881 fps / 244 fpe

shot 5 879 fps / 243.fpe

shot 6 896 fps / 253 fpe

shot 7 901 fps / 256 fpe

shot 8 891 fps / 250 fpe

Standard Deviation is 11.15, spread of 30. Has gone as low as Standard Dev of 4.68 and spread of 20.

So on and so forth to 12, then it falls off the regulator. Hammer spring is 3 turns out from all the way in.

-JP
Click to expand...

That seems good. So my regulator must be set too high?
 
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I can tell you that the adjustment screw is in the end with the fill port, so you will need like an 14-18 inch long screw driver, and not sure what tip it needs.



I'd turn it down until the stock gauge is around 2700, and back off the hammer spring to around 5 or 6 turns out from binding if it is the stock spring. Not sure where to set it if they put in the Pitbull spring.



Edit: this is going to be really hard for you, you hand pump, right? You need to degas for each adjustment and pumping it by hand up to more than 3000 is going to be a major pain.
 
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I have a compressor, so it made life so much easier. I had to empty and refill several times to get my regulator set, so a compressor is very handy for this. Doesn't have to be an expensive one, I have the GSX G3 from Amazon for 2 years now and fill all my airguns with it. Still works perfect. I would invest in a $350 - $500 dollar compressor to make the experience more enjoyable. I use mine not only at home, but in the field as well. Anyway, as suggested, adjust the regulator to 2700-2900ish psi and then adjust the hammer spring around that setting. I don't know if you have any porting or polishing to the barrel or ports on your gun, so my settings may not be ideal for your rifle. Your gun should use about 133 psi per shot. Seems like yours is using about 320 psi per shot right now, more than double for about the same power, not efficient at all.

Also, do you have the K-9 Pitbull build or the AKC Pitbull regulated? Mine is a K-9 build, bigger tube than the AKC build I believe.

-JP
 
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In the old thread he says the AKC regulated version.



I do know they did some maximum tunes for these and it was 3 or 4 shots at maximum power. Very likely this has the largest ports possible, the heavy Pitbull spring, may not have a valve return spring (not sure if they do this), probably polished trigger group.



https://www.pitbullairguns.com/product-page/pitbull-akc-357



It actually says that it only has up to 6 shots per fill which is more than the DIY kit that I bought.



What You Get:

New Benjamin Bulldog (Black)

Transfer Port Power Modding

Extended Reservoir

Fill Probe

HUMA Regulator
Barrel Supports
Picattiny Bipod Rail
Pitbull Good Dawg Trigger Kit

Pitbull High Performance Breech O-ring (plus extras)

Pitbull Power Spring

Barrel Crowning

Barrel Lapping/Cleaning

Hammer Polishing

Full Lubrication on necessary parts

Velocity Tuning/Adjusting

Benjamin Owners Manual, Cleaning Kit and 5 Round Magazine
Click to expand...


 
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I have a compressor, so it made life so much easier. I had to empty and refill several times to get my regulator set, so a compressor is very handy for this. Doesn't have to be an expensive one, I have the GSX G3 from Amazon for 2 years now and fill all my airguns with it. Still works perfect. I would invest in a $350 - $500 dollar compressor to make the experience more enjoyable. I use mine not only at home, but in the field as well. Anyway, as suggested, adjust the regulator to 2700-2900ish psi and then adjust the hammer spring around that setting. I don't know if you have any porting or polishing to the barrel or ports on your gun, so my settings may not be ideal for your rifle. Your gun should use about 133 psi per shot. Seems like yours is using about 320 psi per shot right now, more than double for about the same power, not efficient at all.

Also, do you have the K-9 Pitbull build or the AKC Pitbull regulated? Mine is a K-9 build, bigger tube than the AKC build I believe.

-JP
Click to expand...

I was using the hand pump for exercise, but I am thinking about it getting a compressor now that I picked up a second PCP. I could not find the GSX G3 though. You're getting 250 ft. lbs per shot roughly for a lot of shots, that is pretty good I think. I am not sure how much I could be getting. My last 5 shots were using 145 grain Benjamin eXTREMES and the first four were regulated. Nice power but a lot of air like you said:

Notes

Pellet:
Weight: 145.0

Shot count: 5
Low: 893
Hi: 923
Avg: 910
STD Dev: 11.8
Spread: 30.0

923 fps 274.5 ft. lbs
902 fps 62.3 ft. lbs
909 fps 266.3 ft. lbs
923 fps 274.5 ft. lbs
893 fps 256.9 ft. lbs

The fifth shot wasn't bad but no longer regulated. 



Yeah the website says 6, I'm getting 4. I did send the gun back and pitbull are going to check it out and fix it, so that is appreciated. The version I got was the Texax Edition (no longer offered) which was the AKC with a bunch of accessories and a scope.
 
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Amazon.com: GX CS3 PCP Air Compressor, Auto-Stop,Oil-Free, Built-in Water-Oil Separator Filter, Powered by Car 12V DC or Home 110V AC w/Converter,4500Psi/30Mpa,Paintball/Scuba Tank Compressor Pump : Tools & Home Improvement

Amazon.com: GX CS1-I PCP Air Compressor with Built-in Power Adapter, Auto-shutoff, Oil &Water-Free, 4500Psi/30Mpa, Power by 110V /220V AC or 12V DC, Air Gun and Paintball/ScubaTank Compressor Pump, HPA Compressor : Tools & Home Improvement

Both of these have great reviews on youtube. I only have experience with the GX CS3 and has held up for 2 years now. It is good that PitBull is taking care of your problem. I have dealt with them very little, but they have always been helpful and nice on the phone. Hope everything gets sorted. I really like the shot count mine gets, as I get more target practice before a refill. I can turn the hammer spring up and get more power, but I would sacrifice shot count and I want a balance of power and efficiency. I feel like I get both with my big bore while maintaining a compact-ish size and weight. I view my bulldog as a all around hunter, fun for targets, but can also hunt small game, medium game, and large game by adjusting the hammer spring and ammo weight, I can hunt it up or down. As I mentioned, the compressor just makes it more enjoyable to shoot, and makes refilling faster for adjustments and testing.



-JP
 
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@bd2021 I realize the gun is not getting the six regulated shots as advertised, but the way it is currently tuned it is a high power beast; a deer and hog slaying machine! Three to four high power shots with that close of a fps spread is great for somewhat longer range accuracy needed for that game or even long range ground hogs too. I'd keep the high power and four shots rather than detuning it to get six.
 
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Greg_E, no problem. I will be on vacation starting April 2 through April 15ish. I did not max out my ports. I think I am at the middle ground, possibly a little above, nothing huge in porting. That said, I have ported my barrel and transfer port and polished them both to a mirror finish. Dremel tool works wonders with polishing compounds. I have also polished my breach with the dremel tool. I have reshaped my poppet valve to make it more aerodynamic and lighter and removed the poppet valve spring. The gun will reseal after being totally empty, just have to make sure its cocked and held straight up. Once it starts to fill, un-cock the gun and let it fill as normal. Refills are normal after that as long as its not ran empty. I polished my hammer as well. Trigger assembly surfaces are also polished to a mirror shine. Tutorials on the trigger assembly can be found on youtube. My trigger is now smooth as butter and breaks so clean and light, way, way better than factory. Just don't take too much off as you can ruin it. You can actually test the trigger assembly on the outside of the gun if you rest it on the pins before re-assembly. There is a video showing how to do that. Lastly, I cleaned and polished my barrel. I did each of these a step at a time and tuned my gun around it. I wanted to see if there was an improvement with each modification and there was. 10 psi here, 20 there, and 30 there, so on and so forth. I chose 12 shots as my goal, I could do 10 and have more power or 15 and have less power, but I chose 12. I can still shoot once it falls off the regulator because it is set at 2900 psi, so it will still shoot just not shooting on the regulator at that point. I think Pitbull recommends 2700 psi on the regulator, but I experimented with my gun and found it likes 2900 psi and tuned around that. In my opinion I believe that porting is a big factor, but polishing and paying attention to how the air flows and transitions from its journey through your gun is what needs special attention. Take your time think about how can I make the air travel smoothly with little to no turbulence. Smooth transitions, no hard angles, burrs, and smooth surfaces.

-JP
 
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The valve return spring is where one of the extra power is from, I still run the stock spring. I may need to fix that in the future. Going to see how it shoots after running a reamer one the leade, I think that will fix the issue I was having. Loading a 125 grain round was supper easy, loading a specific 155 grain round was hard. I pushed one of the 155 grain back out the breech and found that it was embossed a little over half way, and the oil groove lined up in such a way that I think it needed more pressure to get it moving. I was getting 185fpe with the 125 grain and the same 185fpe with the 155 grain. Really just changed the taper a bit to a shallower angle, should do what I want. This was with the stock barrel port, but valve and transfer at .210 (a #1 drill). trying to stay conservative with the power.

It's all back together and ready to test, but I don't have room in my garage to set up my trap right now, and shooting it the other way would point at the neighbors house with nothing buy 1 inch boards and siding to stop it if there was a miss. Too dangerous to go that way because I know it will barely slow down with 1 inch pine. The other direction would be concrete block and a fence before it got into the neighbor's yard and a total of over 100 feet between building, they are a little higher too so it would in up in the yard if it made it through everything. Getting about 12 inches or a little more through a bucket filled with rubber mulch, less into the bucket with old denim.

In theory I have a 700fpe beast I can use for more power, but in practice I've only had it in my hands for 3-4 days since it arrived in February, not sure if or when it will come back from service, might turn into a refund at this point.
 
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Greg_E, absolutely, removing the valve spring gave me huge gains, but I think if everything is done as a unit, then everything works in conjunction with one another. My gun used to shoot violently with the same power because I was trying to just force air through and wasting a lot of air. I think a lot of folks do the same thing and just port out huge holes and try to ram air through and make power and that is fine for some people. I wanted to make my gun shoot nice and smooth but yet create good power and high shot count, at least for a big bore. Mine shoots so nice and calm now, its deceiving how much power it makes. I do have a super high power big bore, its a XP fifty-eight, .58 caliber. An older rifle with a 36" barrel. Just got it maybe 2 months ago. Its capable of 1000fpe, but I have only shot 1 round ball through it to make sure it works. It is a beast, but I love shooting my Bulldog more because it uses less air, is cheaper on ammo, and just shoots so nice. I have pushed it to 200 yards so far and it is very accurate at that distance. While I am on vacation I may try 250-300 yards just for fun to see what it can do.

-JP
bipod1.1648649991.jpg


XP 58.1648650028.jpg

 
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