Arizona,
If I had to guess, the gun does have 3000 psi in it, due to the reading on the bottles gauge.
The gun gauge is reading 2000 (or thereabouts, those cheap gauges aren't known for their accuracy),
which would be correct, because now that a regulator has been installed, you are now reading the regulated pressure of the regulator. This is normal.
Tom Holland
Field Target Tech
Fieldtargettech.com