One sign of excess pressure is loose primer pockets.
If you're loosening primer pockets on the first shot, it's definitely excess pressure and time to back off. In ARs usually I see ejector hole marks (not just swipes, but actual raised circles on the case head) but not always.Those marks can be a sign of over pressure, but the absence of them doesn't mean you're OK.
If a case is reloadable 6-8 times with tight primer pockets, pressure isn't close to max. I consider max where a case is reloadable 3-4 times (assuming no other pressure signs either), and I've seen well above 2750 in 16" barrels with 75/77gr bullets with that criteria, with several different powders. That is mostly using LC brass, sometimes I'll use Win or PMC brass as well.
One side comment about ejector swipes as a pressure sign - excess headspace (even .010") or an overgassed action can both cause these even with lower pressure loads. I consider them false pressure signs in those circumstances.
Also - correlating your velocity to a factory load means nothing if you aren't using the same powder. Even then, you have no idea what actual pressure is from the factory load in your barrel, only a loose guess.
