Tuning Strange results

[bd2021]

So you may or may not recall that I picked up a Pitbull Texas Edition (aka a Pitbull AKC with scope, bipod, and other goodies).

I had trouble right from the start.

Eventually after several months I eventually convinced Pitbull to take a look at the gun. They determined that the regulator and regulator gauge were bad, and claimed I was essentially shooting an unregulated gun. I don't really buy that the regulator was so bad that it was like it was not there, but that is beside the point. It looks like they also replaced the front gauge aluminum that was scuffed when I first got it, which was nice. Paul reported that the regulated gauge was reading 2700 but cautioned that it might read 2800 psi for me. It did, coincidentally. It is 2800 to 2850. But I am looking for 8-10 regulated accurate shots for Coyote hunting, so if I am ultimately able to get that, I'll be happy.

Anyway, still hand pumping, pumped it to 4500 psi, tested with 135 grain BT LDC from Griffin. The results weren't that great, in fact, from my perspective, worse than before I sent it in...but more on that later.

Here are the results.

Graphically:

After calling Paul at Pitbull air, he said they tested it with 50 rounds after the repairs, but without a chronograph. Paul told me they don't have lab coats or beanie hats at Pitbull airguns. Too bad, really. Nothing wrong with being methodical from my perspective, but oh well. 

Even so, while I paid shipping to Pitbull air, they spent time, energy, and 50 rounds of lead as well as return shipping, so that was also nice. A plus for pitbull air.

Anyway, so I cleaned the barrel, pumped it back to 4500 psi, and tested with the 145 Gr. Benjamin Extremes, and got better results.

It both cases(135 Griffin and 145 Gr Benjamin eXTREME), the power spring was turned back 3 full turns from full tight. 

I'm new to this, but I am guessing I was wasting air on the 135 and need less hammer spring. Either that or the fouled barrel had more of an effect than I would have guessed.

Anybody got some guidance?

Meantime, I need to buy a compressor. This hand pumping takes too long to dial in the gun.

All in all, I've had better luck with a used crown .25 I picked up and modified. Eventually I may end up disassembling and rebuilding this pitbull airgun, especially if I don't get anywhere with an electric compressor and chronograph testing. On the other hand, this pitbull did drop a coyote so I am still happy about that. Guessing a .30 FX crown or edgun leshiy 2 would have as well.

 

[Airgunmann]

Regulators tend to take a bit to settle in as well but there is nothing wrong with the 145 Benjamin string that's what I would stick with 

 

[bd2021]

Regulators tend to take a bit to settle in as well but there is nothing wrong with the 145 Benjamin string that's what I would stick with

Thanks. You don't think I might get better results with the griffin if I relax the hammer spring some?

Well, I just ordered a compressor so I guess I will see soon enough.

 

[Greg_E]

That thing is screaming compared to mine. You might get more even but lower speeds by installing the stock valve return spring in front of the valve, I think they remove it when they tune it up. What is your pressure after 5 shots? Mine went from 4500 down to about 3050-3100 psi for all ten shots.

All that said, I have not tried lighter ammo yet, only the 155gr that I cast. And with that mine seemed far more consistent and easy to predict by turning the hammer spring. I do think I want to put the heavier Pitbull spring in and readjust it for current power level.

With the power you are getting, I'd try to tune it for the lighter and faster ammo. Much flatter shooting above 900fps. 200fpe with a 125 or 135 grain would be in a good place for medium size game. Dial the spring out another full turn and see what happens, maybe two turns.

I do wonder if your regulator isn't breathing properly on the vent side. No more hole drilled for ambient pressure, Huma says to leave a paper thickness of free play on the tube to vent. I took a file and cut a small notch in the end of my tube to make certain it had some airflow to the backside of the regulator. Maybe that could be an issue with yours??? Should have taken a picture before I put my stock back on to demonstrate.

Also you mention fouled barrel, are you certain it is clean now? I had a lot of velocity issues with mine as it was fouling, then it jammed a round part way down the barrel. But that barrel had a problem and I replaced it.



And get a compressor, even a cheap GX should work pretty good. If possible I'd splurge for the 18 volt battery version, but check to make sure it has an AC adapter too!

 

[BackStop]

Regulators tend to take a bit to settle in as well but there is nothing wrong with the 145 Benjamin string that's what I would stick with

Thanks. You don't think I might get better results with the griffin if I relax the hammer spring some?

Well, I just ordered a compressor so I guess I will see soon enough.

Looks to me like you should simply shoot it with the 145 Benjamins and be happy if that consistency holds up! (smile)

P.S.

If you are hand pumping and don't have a problem doing it, save your money on buying a compressor. I guess it depends on how much you shoot and how many shots you *need* during a *session* of shooting. Be that hunting, pesting, etc.

I have 2 cheap ($50 or less) hand pumps (capable of at least 4500psi) and expect them to last the rest of my life. Compressors cost a LOT more, are generally less reliable unless you spend a fortune and even that is no guarantee.

Of course, to each their own and YMMV. (grin)

 

[bd2021]

Thanks backstop,

Okay, you're being factious. I actually would have stuck with the eXTREMEs by benjamin/nosler. They were devastating on the coyote which I like. Even though I have come to hate coyotes, I don't want to listen to one die slowly in pain. Not yet, anyway. (If it attacks my dog, well then maybe). But the benjamin/noslers were out of stock everywhere. I think I bought the last two boxes on the planet. If you know of a source, please let me know. And, in any event, the griffin LDC 135s were shooting fine before I returned the gun for work, at least judging by the chronograph. I just learned there are some Flat nose 147 grains from Benjamin at about $0.50/shot, so I might check that out eventually.

On the hand pump, I didn't mind pumping, but I am getting callouses and it limits my learning this gun. It is not as plug and play as I had hoped. Another idea I am wondering if these huma regulators don't like hand pumps. 

Especially since I am hoping to test out all of the ammo I've picked up to see which one this gun likes the most for accuracy and kill power at a distance (See https://www.airgunnation.com/topic/3d-printed-357-ammo-boxes-for-transport-to-field/?referrer=1.), I picked up an omega trail charger, as it seems quiet, beefy, and quick enough if you're not filling up whole 100 cu. ft. tanks.

 

[bd2021]

Thanks for the tips Greg_E. I ordered an omega trail charger. I wonder if filling the gun too slowly with a hand pump might adversely affect the regulator....just another crazy thought. But in order to do some testing I think I need the compressor. Getting callouses on my hands at the moment. The hill hand pump I have works great, but the handles are painful. I have an FX hand pump too with much better handles but it doesn't work as fast as the hill pump.



Oh, by the way, I kept cleaning until the pads came out clean. I am surprised this is an issue though. I would have guessed the lead in an airgun would act as a lubricant. Guess I have more to learn.

 

[Pale_Rider]

After calling Paul at Pitbull air, he said they tested it with 50 rounds after the repairs, but without a chronograph. Paul told me they don't have lab coats or beanie hats at Pitbull airguns. Too bad, really. Nothing wrong with being methodical from my perspective, but oh well.

This guy is off his rocker saying he was able to “tune” your rifle without a chronograph. That’s like a doctor trying to diagnose a heart condition only using his stethoscope.