Gauge discrepancy between tank and airgun

I have had a few guns and the gauge is notoriously incorrect. I changed out almost all of my gauges for WIKA and they are right on with my tank. But good for you for stopping and not taking a chance.

Crusher

Depending on how fast you were filling the gun, you might have been seeing an increase on the gun gauge due to the increase in temperature. (ideal gas law) Basically as the temp goes up as the pressure goes up unless you increase the volume, which you are not. Are you filling nice and slow? That is a good practice, especially to keep from stressing your guns air cylinder. 

I have approximately ten gauges including the ones on my rifles. All of them read within 10% of each other. I have two $3 Chinese ones from eBay that I use as dead heads and these are accurate to + or - 100 psi of the gauge that I use as a yardstick, the one that I scavaged from the SCBA backpack. The two least accurate, are the ones on my rifles but they are still precise enough to safely rely on. It is probably a good idea to have at least one dead accurate instrument to use for comparison.

Aways obey the gun. SAFETY,

The gauge on my crown reads 15 bar less than my tank gauge so I go by the tank . the one on my wildcat is spot on with the tank and compressor gauge . I tend to go by by whichever gauge reads highest . I so need to get some wikas for my guns .

I think the best way to avoid any problems caused by overfilling will be to get a high quality gauge like or similar to this one
https://www.amazon.com/SSI-TECHNOLO...sr=8-62&keywords=5000+psi+pressure+gauge&th=1

install this gauge on a tee fitting then to your tank and to what your filling. Use the reading on this gauge as a guide to the accuracy of the gauges on your guns and take note of the pressure differences. The problem is most tanks even the $800 ones have a $25 guage on it which are more prone to inaccuracies. Buying one quality Guage will give you a tool to keep track of your other gauges. Remember the readings on your guages will change over time so do the checking more than just one time and always wait a few minutes to allow for the temperature of the air tanks to equalize.

+ what Brian said....