I dont ever clean the rifle in the middle of a load development. I gave gotten my complete load development down to between 80 and 120 rounds, in most cases, so no need to clean in the middle. Most of my cartridges that burn 32-42 grains of powder ranging in velocity between 2650 and 3100 all seem to go 250-300 rounds before I see any degradation of accuracy. Some of the larger cases burning slower, dirtier powder might not go that long.
When I change bullets, powder, or start a new load development I clean the barrel. I clean all the carbon out and most of the copper. It takes forever sometimes to get every little bit of copper out, so I just get the carbon out and clean the copper until there’s just a hint of blue on my patches. I clean my barrels every 100 rounds typically but my load development usually is over by then.
I will generally clean when changing powder or bullets, but that is simply another "load development. I also send a few rounds down range to "foul the bore", ensure my set-up is working properly (chronograph), and that I'm on target. It also gives valuable info on a clean cold bore shot compared to the second shot. YMMV
Well depending on the barrel quality & bullet, a barrel can copper foul out by ~some number of shots.
And if you're leaving petroleum products in the bore -it has to be burned out before establishing stable fouling.
I have actually seen a barrel that would copper foul out by 10shts.. I had to fire lap that bore with Tubb's FF before proceeding with any development.
For ladder testing you only need 30 good shots. But beforehand, shoot a 5sht group, just to prefoul a cleaned bore.
If that's inline with your cleaning plan & field use, then clean after the ladder session, and do the same when your ready for group shooting (incremental load development).
If you plan to go 50shts before cleanings, do that. See if it will -before groups open from copper.
If you want to to go 100shts between, then in my experience you'll have to do more than just choose it. You can go to a dry pre-fouling plan and get a lot more GOOD shots between cleanings.
Not sure what your goals are. If I'm changing hunting loads after the season, I'll do it in the "dirty" rifle, usually less than 200 rounds since the last cleaning. Then I'll clean and shoot my off-season practice rounds after. When the season comes around again I'll have a nicely fouled but still accurate barrel with a load I know what'll happen with.
High-precision stuff out of fancy barrels I'd do differently.