Without using a sled? I read a lot about setting up a new load, incremental increases in powder, seating near or on lands, this or that change and gauging the results. Is there the assumption here that everyone is using some kind of aiming/shooting device to help eliminate the human variable?

If I am shooting off sandbags at the local range, am I just wasting my time trying to improve accuracy through load development? Is any change I make and resulting difference that I might see likely just the result of a slight change in my technique due to more practice behind the rifle? Or weather, or perhaps the guy next to me shooting a muzzle brake on a cut down AK47 and splitting my head with every shot?

Just trying to figure this all out