Re: flattened primer?
Safest way is to invest in a Chronograph. Pressure and vel are directly related. Compare your vel to those listed in recent load manuals. All are rated at SAAMI max so there are no whimp loads.
If you vel is sig higher then print, you are treading on high pressure despite what your case condition may be.
It is quite common for stand cases to be loaded to magnum pressures. However, that is in excess of SAAMI specs but could be "safe" in the right rifle.
Any time you experience pressure signs like sticky bolt, extractor marks, loose primers, you are way over magnum pressures and backing off is prudent.
Now for the best part. Almost all rifles shoot their best at less then max pressures. So, if you want a great shooting setup, avoid going overboard with your loads.
If you want a particular vel level for a certain bullet weight, get a bigger cartridge. The rifle will shoot better and you will keep all you important bits attached to you.