My 7MM STW is a 700 Remington with a 26-inch Shilen stainless barrel which was installed and chambered by Shilen. It gives full, maximum load velocity with what should be less than maximum powder charge handloads. I guess it probably has a tight chamber and the throat was cut for a small jump with the specific bullet I use. (Tight chambers and short bullet jump both increase pressure and velocity.) If one did not work up loads for that rifle with the aid of a chronograph he probably would have worked up to what was listed as less than a maximum load and wondered why the primers blew. Anyway, if a chronograph shows too high of a velocity the gun would also have too much pressure. Nothing is free. If so, handloading could solve the excess velocity/pressure problem by using a smaller powder charge. Chronographs are worth having. Another factor could be barrel temperature. Any time I shoot a series of shots where the barrel is warming up and am using my chronograph, the velocity is greater with each shot. For most powders, higher temperatures cause higher pressures and higher velocity. I have been handloading for over 40 years but was surprised during a moose hunt a few years ago. I worked up hot loads for my .338-.378 Weatherby. While doing this I did not let the barrel get hot. That is, I let it cool down between each shot. I always figure there is no good reason to let a good barrel get hot, except maybe for prairie dog shooting. During the moose hunt I shot a moose and my guide could see the bullet hit the lungs. It just stood there like nothing happened and I would have just waited until it dropped. But my guide told me to shoot again, so I did and again hit the lungs. I did not notice any difficulty extracting the first cartridge but the second one was difficult to extract. The moose continued to stand there and my guide told me to shoot again and this time the moose dropped, and I could only get the third cartridge extracted with a great deal of difficulty. Each time I shot, the barrel got warmer, and velocity and pressure would have increased. In addition it was raining all the time and I was hunting with an emty chamber and a loaded magazine. The cartridges were wet, so the water adhearing to them would have taken up any space between the cartridges and chamber, in effect producing a tighter chamber than I had when working up the load. Anyway, I would guess the barrel on your rifle was warmer during the 4th and 5th shoots than during the previous ones.
