Jack, how do you know how far to put the dowel down the barrel? No doubt a rather simplistic question. Also what size dowel would you use?
long
You put the dowel in the muzzle as a counterpoise to the OAL guage's sliding rod. You slide the bullet in using the OAL guage's rod and you slide the dowel rod in until it touches the bullet. Then using two hands ( one on the dowel rod and one on the slider of the OAL guage ) you can tell by feel when the bullet
just makes contact with the lands. You really need to manipulate the sliding rod of the OAL guage with your thumb and index finger while keeping a couple of fingers on the barrel of the guage itself to be sure it is keeping the case seated.
Any dowel that is sufficently narrow enough to slide between the lands without any noticeable friction will work. Ex. .25" works fine for .30 cal.
Of course you really need to read the instructions that come with the guage or contact Stoneypoint to undersatnd how to use it properly.