Started up one of my custom (read: bastard) 502s last week after a long winter and realized the gauge was showing zero oil pressure. Oddly enough, the bottom end sounded fine but the valve train was starting to make a little noise... so I quickly decided to shut it down,

After pulling the distributor, I went into the toolbox and grabbed my pre-oiler / luber. This is not just a straight pump shaft, but one with the aluminum bushing that simulates the distributor housing allowing oil to flow into the camshaft and up to the valve train.

Anyway, with an electric drill set on high speed I could only get about ~5psi on the (schitty electric) oil pressure gauge. For redundancy, I hooked up a spare (even schittier) oil pressure sender and gauge which confirmed the initial results.

...is this right, or is something not working correctly in my pump?

Please correct me if I'm wrong, but most cordless drills are easily capable of 1000 rpm. Let's also not forget that the distributor turns 1/2 the speed of engine RPM. So even if I was only getting 500 rpm out of my drill, it would otherwise be simulating 1000 rpm which should otherwise give me plenty of oil pressure. Especially considering this was a cold motor with 10/30 weight.

I dropped the pan this evening and pulling the oil pump off and apart. The pump looked a little chewed up on the actual rotor lobes, but nothing horrible. Unfortunately, the relief valve assembly shot across the garage floor as I was pulling the spring pin. I recovered everything except for the piece that goes over the top half of the spring. The actual valve was still there. The valve could still slide in and out, but there was "some" binding that did occur at points in the travel.

Regardless of all this, a new oil pump will be ordered first thing tomorrow morning. I just want to make sure that when I hook up the drill motor again, I should expect to see more than 5 psi.

When I did my 502, I could get over 50psi on my cordless drill.

with my milwaukee 1/2 '' drill on full trigger i get 60 psi out of both og my 502's,,that is with a mechanical mac oil pressure gauge..

Not if it's a cheap low voltage cordless spinning a BB oil pump. I once spun an HV pump in a BB with a cheap a$$ Cummins 120V 1/2" drill. It hit 40lbs. and the drill went up in a cloud of smoke!
You may want to think about going to a better oil than 10-30, not that it has anything to do with your problem. Just say'n.

I run 10w30 Amsoil Dominator and I get 50+ pounds from a 19.2V cordless. You've got a relief stuck open or a serious clearance problem. I'd pull the motor and carefully disassemble the oil pump first.

The drill I'm using is an 18V Ryobi that has otherwise been a great little drill for me. Also, the bottom end has maybe five hours on it, so clearances should otherwise be OK... even though the original (late) engine build was a stumbling alcoholic.

Thanks for the feedback everyone.