That is pretty much the same way I do it. I find trying to use the breech end is more difficult as there is usually a sharp edge where the breechplug mates with the rifling and makes getting a good measurement difficult. I also find that usually once the slug is started I can push it with a ramrod or longer wooden dowel. I use roundballs as I have a lot available and just flatten them a little to make them larger than the bore. You usually can tell by the feel when pushing down the barrel if there is a large difference in diameter as you go. I disagree a little with the statement that bullets should be smaller than groove diameter. I find especially with cast pistol bullets for my revolvers and automatics that the bullet about .001 larger than bore diameter shoots best.