FWIW, when you fill from empty to full pressure, the compressed air will be hot, in which it expands so as your gauge may indicate 160psi, as the compressed air cools, the indicted pressure will drop so be aware this is normal and NOT a leak.
Great observation.
I'd like to observe one other thing:
We are still using tapered pipe threads...In 2023.
This is an absurdity all its own.
Tapered pipe threads are one step removed from steam engines and horse and buggy.
The problem of leaking fittings has been solved long ago. SO WHY DO WE PERSIST IN PROPAGATING AVOIDABLE PROBLEMS?
If your fluid conveyance system needs some kind of dope on the threads, it's a bad design. Threads are not seals and seals are not threads.
A standard ISO 6149 port is good to well over 400 bar with adjustable fittings, doesn't leak, and is a global standard with parts available at every hose shop on earth. Every cartridge valve and other type of actuator you can dream up is offered in this standard. You can adapt it to anything else pretty easily.
There are compelling reasons to abandon the archaic tapered pipe thread standards and only inertia and laziness justify keeping the atrocity of poor design that is the tapered pipe thread.
Someday, I'll post my rant on pipe threads. Today, you just get the short version.