Listing a shorter than normal OAL is more than likely a safety factor that powder and bullet manufactures build into their load data. When you increase the OAL of a cartridge the speed goes down but the pressure goes down at a higher rate. If they gave the max load at the longer OAL and you loaded to a shorter OAL the pressure would be over the max for the cartridge. If you look at Allient Powder load data they only list a max load of powder and a "min." OAL. It can only be assumed(???) the listed Max is the max pressure for the cartridge and any increase in OAL will give a lower (SAFER) pressure.
😆 just what the hell are you talking about. If he would just read in the Hornady manual (Or on the web site) internal ballistics section his answer is there. But even this doesn’t explain why he can’t seat to the recommended depth with that bullet powder combination even though Hodgdon lists 46.3C max of 4064, 165 Horny @ 2.750. He’s either doing something wrong, or his brass is lacking in case capacity. Please don’t confuse the guy.
https://www.hornady.com/team-hornady/ballistic-calculators/ballistic-resources/internal-ballisticsTo illustrate the effects of variations in bullet travel before the bullet enters the rifling, we'll compare a standard load with adjustments made only in the bullet's seating depth.
In a "normal" load with the bullet seated to allow about 1/32nd of an inch gap [Fig. 29] between the bullet and the initial contact with the rifling, pressure builds very smoothly and steadily even as the bullet takes the rifling. Pressure remains safe throughout the powder burning period [Fig. 30], and the velocity obtained—3,500 feet per second (fps)—is "normal" for this load in this rifle.Seating the bullet deeper to allow more travel before it takes the rifling, as in these next two illustrations, permits the bullet to get a good running start [Fig. 31].
Powder gasses quickly have more room in which to expand without resistance, and their pressure thus never reaches the "normal" level. Nor does the velocity; with the same powder charge, it only comes to 3,400 fps [Fig. 32].When the bullet is seated to touch the rifling, as in the accompanying illustrations, it does not move when the pressure is low [Fig. 33], and not having a good run at the rifling as did the other bullets, it takes greatly increased pressure to force it into the rifling. As the rapidly expanding gasses now find less room than they should have at this time in their burning, the pressure rise under these conditions is both rapid and excessive [Fig. 34]. Velocity is high at 3,650 fps—but at the expense of rather dangerous pressure. Many rifles deliver their best groups when bullets are seated just touching the rifling. Seating bullets thus can be done quite safely if the reloader will reduce his charge by a few grains. The lighter load will still produce the "normal" velocity without excessive pressure.
