A/C charged, then overcharged, but still low pressure

[Mike1261]

I just replaced the AC compressor in my E53.

Prior to replacing it, it would take 10-20 minutes for it to start blowing cold.

Ambient temperature is 80F so everything suggests I want to see 40-50psi on the low port.

It took 20 minutes to get a 12oz can into the system.

I then switched to the second can and was watching the pressure gauge to determine when the system was full.

15 minutes later the second can was empty and the gauge was still reading about 38psi.

The spec calls for just shy of 16oz in the system. I now have just shy of 24oz in the system. AC blows pretty cold but I'm concerned that it's overfilled and that the pressure still appears low.

I did also replace the dessicant in the drier fwiw.

Not sure where to go from here. Even if I evacuate the system and start over, how on Earth do I know I'm at 440 grams if I can't look at the pressure reading. I suppose I could keep unhooking the canister and weighing it but that seems a bit annoying, and I'd lose some freon every time I purge the line too so would throw off the result there as well.

Thoughts?