Crosman 1720T air gauge question.

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SAZ

SAZ

Member
Apr 18, 2020
306
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Arizona, United States
So, I've been stumbling and bumbling my way through trying to do a little tuning on my 1720T pistol recently and I've noticed something I thought I'd ask other 1720T owners, or any other Crosman pistol owners about.
I notice when I (slowly) fill the pistol with air just up to where the red line starts at 3000 psi on the gun gauge that the liquid filled gauge on my Great White air tank is only showing a pressure of 2500 psi. The tank is filled to around 4000 psi and has no problems filling up my other guns that use more than 3000 psi so there doesn't seem to be any issues with the tank.
Is there something obvious I'm missing here? Any guesses at which gauge has the higher probability of being correct?
Correct me if I'm wrong (I know you will ;)) but this sort of messes with tuning if I was attempting to fill the gun to, as an example, 2750 psi to start a shot string over a chronograph from there. If the gun gauge is off then I'm underfilling, if the tank gauge is off I'm potentially overfilling.
Ideas?
 
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SAZ,
First, to begin with, the gauges on Crosman/Benjamin platforms, regardless if it's a rifle or pistol, are not high end gauges. I think these gauges are only about 8 bucks, and they are for a general reference. I would almost guarantee that if you took 3 or 4 of those gauges, and pressurize them to 3000 psi, I'm sure they would all be different. I would trust the gauge on your larger fill tank, than the gauge on the gun.

Tom Holland
Field Target Tech
Fieldtargettech.com
 
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Pressure gauges of all kinds are notorious for disagreement.

Consequently I do all my tuning with little regard for what my tank gauge reads, other than noticing if it's far different than what the gun gauge reads. I developed that habit when making use of community air tanks at competitions, where depending on an unfamiliar tank gauge costs victories.
 
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bf1956,
There was an older discussion on GTA forum about the same topic.
A person there said they had good luck with this gauge: https://www.mcmaster.com/9767T21/
Also found a reference to this gauge on eBay: https://www.ebay.com/itm/122793977614
I have no idea if either of these work well or not. Good luck and let us know if you try one!

I think AirNGasman has a good suggestion above to remain consistent while tuning if the psi on your two gauges isn't very different.

I wonder if you could make note of the psi indicator position on your air gun gauge when you fill it to your desired psi and then (no matter whose tank you're using) you fill it to that position which should get you pretty close to your desired fill psi? Could be wrong, dunno'........
 
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"I wonder if you could make note of the psi indicator position on your air gun gauge when you fill it to your desired psi and then (no matter whose tank you're using) you fill it to that position which should get you pretty close to your desired fill psi?"

I usually do that by putting small dots on the glass (or plastic) face of the gun gauge with a fine-tip marker, marking not only the correct fill pressure but the refill pressure. Comes right off with lacquer thinner with no harm to glass, however could damage some plastics. Also, some gauge faces will rotate; easy enough to check that with a finger-tip or two.
 
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Good Morning Everyone,
Thought I'd post a short update:
I ended up installing a Huma regulator in the 1720T pistol and removing the gauge and spacer, so that cured the inaccurate gauge question. ;)
  • It took me less than a half hour from start to finish.
  • I spent around $115 or so for the regulator and a regulator rebuild kit with all the o-rings and stuff just to have it on hand. I ordered it on Monday and it was here by noon on Thursday from overseas. Amazing how they are able to do that!
  • I drilled out my (already modified) air transfer port to 0.110". Had a couple of factory non-modified atp's on hand in case I screwed up.
  • Regulator came from Huma set to 115 bar.
  • No changes to swapping out hammer springs, etc. I used the stock parts that came with the gun.
  • Hammer spring at zero, hammer stroke at zero.
  • Shooting 10.34 grain pellets, it instantly went from around 20 "ok" shots to 40 shots pretty consistent in the 11.0 - 11.5 fpe range for field target use.
  • Starting fill pressure according to my Great White air tank gauge = 2800 psi. Ending pressure somewhere around 1200 to 1400 psi. Kind of hard to tell without a gauge. I was using the chronograph to track things and velocity dropped off quickly after 41 shots.
  • I hope all this helps someone out there in some way.

  • 1660832982256.png
 
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Excellent post of real-world results with your Huma regged 1720T, SAZ. Glad you got such great results; but being a big believer in Huma, I'm not surprised. One suggestion.

If you shoot FT competition with it, since you no longer have a(ny) gauge on the pistol, always use YOUR OWN TANK in competition. Don't assume tank gauges are more accurate than others; they aren't.
 
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