On Jam:
This is the no man's land of terminology

The first that I heard of the term jam used in reference to reloading, was in my reading in Precision Shooting, perhaps 30 years ago, when it was almost entirely devoted to benchrest. Prior to that time, I had never seen the term used for that purpose. Back then (and now, for me, and others of the old school) , jam was the maximum length that you could seat a bullet, without it being pushed farther into the case as the round was chambered, using the neck tension that would be used for the actual loads. The common method for determining this dimension was to size a case using whatever bushing the plan was to load with, seat a bullet a little long, measure the OAL, chamber the round, or dummy round, and measure again, to be sure that the bullet had been seated a little farther into the case by the round being chambered. By looking at the two measurements, which at this point could be taken off of the point of the bullet, and calculating the difference, and adding the amount that one wanted to be "off jam" it was a simple matter to reduce the total length of the combined seating stem and cap of a Wilson seater, by like amount. At that point one could do an ogive to head measurement, and record it for future reference, when the original set up bullet might not be available. If one was seating close to the point where the bullet first made light contact with the lands, one referenced that range of seating depths as so many thousandths into the lands, off the lands, as touching, or longer than or shorter than touch. It was only some time later, with the advent of the internet, and a general lack of any formal source of definition that jam was converted, ( some would say corrupted) from a noun to a verb, as in seating jammed, meaning seating an unspecified amount longer than touch, hardly a precise reference, sort of like saying that someone lives on the other side of town, instead of giving a street address. I any case, none of this makes a difference if you are using some sort of standardized procedure to come up with and record a seating depth, until an attempt is made to communicate that to someone else. There's the rub. To really communicate, given that there is no generally accepted definition, the best alternative is to tell a reader your exact procedure. Otherwise, if someone says they are seating so many thousandths shorter than jam, or longer or shorter than touch, the seating depth will not be accurately reproducible by readers unless you tell him your exact procedure for finding jam, or touch.