8mm Mauser 125 gr jacket bullet load

[Patrick Chadwick]

Parashooter, thank you for the very informative graphs. One notes that, in both cases, the pressure peak (one could talk of a spike in the case of the Red Dot) is about the same. It is surely this spike that rams the bullet into the rifing in a matter of microseconds, what happens after being largely acceleration down the barrel.

I think, however, that something is going on that is not (cannot be?) revealed by such simulation. To return to an old analogy: if you place a soft lead ball on the carpet, you can place a hammer head (use a very light/watchmaker's hammer!) behind it and push. The bullet will scoot across the carpet, and will remain unmarked. Now replace the bullet at the starting point, and this time have the hammer head well back, and give the lead bullet a short, sharp tap. If you get it right, the ball will only roll a short way, but you will find a clear flat where it was struck by the hammer. At this point, a non-elastic deformation has taken place, and the energy of the blow has mostly gone into the deformation, not into accelerating the bullet.

So (please bear with me for a few lines longer) a vital action in the rifle chamber is the deformation of the bullet to take the rifling. With the lighter (and thus shorter) bullets under consideration in this thread, the fact that, as already noted, they must be seated a certain minimum length into the neck to obtain proper expansion of the case, also means that they have a longer free bore by comparison with the heavier and longer bullets. In other words, they have a longer way to go and are travelling faster when they strike the transition cone (a.k.a. lead/leade). At that instant, the kinetic energy already acquired by the bullet is partially converted into the deformation necessary for the bullet to fit the rifling. At the contact surface between bullet and bore there will be an extraordinarily high, but extremely localized pressure for a some microseconds.

I doubt that any simulation program available to civilians can calculate this, neither can one do so with devices that measure chamber pressure, as this is a matter of contact pressure. But this is what I mean by the necessary "whack". And as this is about deformation energy, it will (amongst other things) depend on what exactly you are trying to deform, and how much. I.e. bullet size, hardness, taper of the throat etc etc. So be be wary of the "universal load".


Patrick