Can you tell me when we reload how much do we loose in fps each time we crimp there must be a weakening of the crimp. Therefore affecting the “boiler” pressure, thus the speed of the shot.Have you ever found anything in your time that you can share with me on this issue.
I just love this question as I can point you to other sources that have done all the work and I don’t have to take any of the blame myself.
The Hodgdon Powder Shotshell Data Manual (Hodgdon Powder Company, 1996) hardcover reloading manual, the one with the dark red cover that I have hiding under a pile of stuff on my office floor somewhere, has a nice article on what happens to velocity when hulls are reloaded to exhaustion. I’ve also seen similar articles in other publications. The conclusions are all the same: it doesn’t matter.
The Hodgdon lab runs 15 target velocity reloads through the same Remington Premier hull. Pressures and velocities changed very little from first to last. By very little I mean a couple of hundred PSI and a maximum velocity variance through all fifteen firings of only 8 feet per second. Hodgdon specified that they used “factory equivalent crimps or an adequate crimp depth of 0.055″. .055″ is just a tiny bit less than 1/16”.
They also tested a Remington Premier 28 gauge hull. It lasted seven firings with a maximum pressure variance of 500 PSI and max velocity variance of 13 feet per second.
They point out that you may not get the same performance out of other brands of hulls and that most Reifenhauser hulls (the ones with straight walls and little vertical lines on the outside like Federal and Fiocchi plastic hulls) aren’t designed to last as long.
But the lesson seems clear. As long as you can get a factory crimp and use a new wad, the age of the hull doesn’t seem to affect performance when used with target loads.
What they didn’t answer was whether heavy hunting loads using slower powders would perform the same way, or whether they would need more crimp resistance to allow a uniform burn of the slower powders. I don’t have an answer for that as I haven’t done the work and I don’t have someone to crib from.
By the way, this hard cover Hodgdon manual has a great deal of very interesting information that would interest Junior Technoids apart from the reloading data. You will be very surprised at what certain changes in components or even just crimp depth can do to pressures and velocity. In one test of crimp depth, using exactly the same components, the Hodgdon Ballistics Lab found that changing only the crimp depth from .030″ to .090″ increased velocity and pressure from 1,308 fps and 9,300 psi to 1,363 fps and 13,100 psi. Who woulda thunk it!
The Technoid writing for Shotgun Report, LLC
(Often in error. Never in doubt.)