I read somewhere about making a cold bore target page that you repeatedly use for the first shot of a trip to the range.
Basically, one target gets the cold bore shot. Then you shoot groups or whatever on another page. You then use that cold bore target with the first shot on the next trip.
A variation was using the cold bore target as a backer behind a fresh target. Then you won't be trying to manipulate the results by holding over or anything.
As far as finding a good load, doing a ladder test or something, then you will just have to be patient and shoot two long 5 shot groups (over the course of an hour for example). You might have to make 3 trips to the range to get good results. That's life. It took me 4-5 trips to the range to get a good set of loads for my 270 M70. I had 5 promising loads 1/2 grain apart that I tried on one trip. I chose 2 good ones out of those 5 groups. I screwed up getting in a hurry and had to make a second trip with the same 2 loads created again, for a total of 3 trips. I picked one load between the two.
The point is that patience is a virtue with reloading. That and not being interupted when sizing, priming, charging, seating.