Confounding Intuition

Whenever I start do something my standard MO is to go and read everything there is to read about the subject.I quickly tend to get past the newbie stage and get to the upper reaches of dangerous.In some cases dangerous is a figurative statement, in others it's far more literal. The important thing to know is that you are dangerous. When you know and aren't complacent you can take extra measures to abate the danger or potential damage.A great example in this realm is reloading ammunition.At it's most basic it's a very simple process:

• Resize
• Trip
• De-prime
• Seat a new primer
• Charge the case with powder
• Seat a bullet
• Crimp

Italics signifies that that step might not be applicable in all instances.Each of these though can have immense amounts of detail once you dive in. Some of this is actually counter-intuitive to boot! Sometimes this comes from things that are wildly non-linear, sometimes from processes that aren't as well documented in the literature.I'll do a deeper dive into a couple of these now: seating and crimping a bullet.I've written another blog post about pressure vs. seating depth among other things. This tells only a part of the story though. The conventional wisdom, as I wrote, is based on some assumptions. Some of those are right, some, not so much.All things being equal seating a bullet deeper into a case will result in higher pressure. But that's almost never the case in real life. The space between where the bullet sits in the chamber and the start of the rifling is called the leade or freebore. The bullet, after it exists the case, needs to jump this gap before it engraves itself into the rifling to continue it's way out the barrel. After the bullet leaves the case, but before it engages the rifling, there's ample space (one to several hundredths of an inch) around the bullet for gasses to slip by. In this case you wind up with more of a "U" shaped curve. As you seat the bullet progressively deeper, you first will get a little bit less peak pressure. Eventually of course you'll be seating it deep enough that the pressure in the case starts to build higher.Now keep in mind for smaller cartridges that achieve maximum pressure inside the case this doesn't amount to a hill of beans. This type of strange, almost unaccounted-for aspects of reality do make a difference.On the other hand, too little powder can cause pressure spikes as well. Some powders, when loaded to really low density can have problems with detonation. Typically powder burns, not blows up -- mind you it burns really fast when it's under pressure, but it's still a controlled burn. In certain cases, the pressure and temperature can cause an actual explosion which drives pressures through the roof and can cause all varieties of failures. Both extremes can be bad.Crimping. Or rather how crimping can lead to a loose bullet.There are two main types of crimp in the world: roll crimp and taper crimp. In this case I'm only going to be talking about taper crimps.A roll crimp is more or less what it sounds like -- you roll the case mouth into a cannelure that's on the bullet. That crimp does a marvelous job in preventing bullet set-back (the bullet being pushed further into the case due to the recoil of the gun).The other type of crimp is a taper crimp. It closes the case mouth against the bullet but doesn't really push it in too far. Pushing it in far causes a problem! (which is why you don't do it)So, if a little crimp is good, why is a lot of crimp bad?Well, you're dealing with two different metals, brass and lead. When you squeeze the brass in the crimping process eventually it'll have no place to go except push into the lead, thus swaging . That's all well and good until the crimp die is no longer pushing in on the brass. The brass springs back, but the lead stays swaged down. Suddenly there isn't any tension holding onto the bullet. Too much really isn't better than not enough!Intuition needs to be tuned. Sometimes the way you tune it isn't at all what you would thing at first blush though.Like anything, a deep dive causes you to turn up all sorts of information that you didn't know. Things you didn't even know existed.