For rifle, I do 5 at each charge. 

For handgun, I load 50.  Reason being I am testing more than just accuracy and pressure with handgun, I need to run enough rounds to test function as well.

Using the ladder method of load development, you only need one cartridge of each charge weight.

http://www.6mmbr.com/laddertest.html

You do need to be a very consistent marksman or use a shooting rest though.

The linked article explains it better, but here goes with a summary:

The ladder method essentially consists of loading a series of cartridges with ascending powder charges in each cartridge, typically in .3 grain increments.

You take the loads out to the range and you shoot them at a single target using the same point of aim. You note the impact of each impact. You should see one or two "sweet spots" where a particular range of charges results in a closer cluster of impacts. Your ideal load will be in the middle of one of those ranges that produces a cluster.



Naturally you'll be watching for pressure signs on each load as well and if you see anything to indicate overpressure you stop.

That method will get you close to optimum charge weight fairly quickly.  After that you play with seating depth to finalize as a general rule.  That, and chronos are cheap enough these days, every hand loader should have one and understand how to use it properly.