Shooting any cartridge with a high primer is inviting bad results.
IMO, one of two things could happen -
1. Slide doesn't go far enough forward to permit firing. FTF = go home with fingers intact and pull rounds apart and reload them to specification.
2. Pistol is out of spec and permits firing without being fully in battery. On feeding second cartridge, slide closes with more force than your initial chambering and that impact sets off the high primer OOB, resulting in a ruptured case, magazine being blown out of the well, and splinters of walnut in your palm. OOB = go to hospital. After recovery, pull rounds apart and reload them to specification.
With high primers, there really isn't any way to tell which of these is going to occur.
As to consistently measuring powder, I believe many reloaders use some kind of volumetric dispenser (powder measure or dipper) and weigh charges to make sure the average is the desired weight. I get +/- 0.1 gr with a Dillon powder measure.
If you are trying for a 3.9 gr charge, your scale should show 3.7-4.1 gr.
A scale which can't measure within 0.1 gr consistently is not very useful, IMO.
Beam scales aren't very expensive, and they aren't subject to fluctuating power supplies, fluorescent lights, etc.
.30-06 Springfield: 100 yrs + and still going strong