Crimping question

[kwallace]

Serious question:

Absolutely every other thing being equal, what does a crimp do?

Let's say I am reloading .357 mag. Same brass. Same primers. Same OAL. Same powder charge with the same powder. Same bullet type and weight. Shot from the same gun (tube fed lever action).

If I crimp, what actually changes other than the bullet being less likely to be pushed into the case by recoil in the tube during firing?

 

[Col. Harrumph]

Let me guess. Probably increases the force required for bullet pull. Especially important when shooting hot loads in a lightweight revolver; I've seen uncrimped bullets walk out under recoil and tie up the cylinder.

 

[edwardware]

Absolutely every other thing being equal, what does a crimp do?

Probably increases the force required for bullet pull.

Yes, and more specifically it increases the pressure built up before the bullet moves. More pressure = higher temperature (adiabatic heating) = more consistent combustion of typical magnum revolver powders, like H110.

Go ahead and prove this to yourself; make a batch of 20, half uncrimped, half crimped. Run them across a chrony if you can, and note the accuracy, velocity, and amount of unburnt powder left over.

 

[Demi-human]

At firing, sometimes the primer or the initial burn of the powder can force the bullet forward, reducing pressure slightly from the increase in volume. This may cause erratic ignition and burn. The result is varying velocity, which is not complimentary to accurate bullet placement. A proper roll crimp provides enough "hesitation" for a complete combustion of the charge. When done right, things become more consistent.
Taper crimp in an auto-loader is for proper function through the firearm. I believe it does not have enough grip to alter the burn characteristics of the cartridge. It might, I just don't think so. But without it, rounds will hang up on feeding, or be unable to fully chamber.

In a straight wall cartridge, bullet setback is enormously dangerous. Because they are very 'efficient' a small amount of setback can increase pressure a very large amount. If, when firing, the rounds seem to be more and more powerful, take one out and measure it. Some times just comparing it to an unfired round will tell.
In an Eagle I was having setback problems, by the last cartridge in the magazine it was trying to forcibly remove my wrists. A stronger crimp would not do. A new sizing die, with more neck tension, solved the problem.

G' mornin' @edwardware! Faster on the draw again!

 

[USSR]

Serious question:

Absolutely every other thing being equal, what does a crimp do?

Let's say I am reloading .357 mag. Same brass. Same primers. Same OAL. Same powder charge with the same powder. Same bullet type and weight. Shot from the same gun (tube fed lever action).

If I crimp, what actually changes other than the bullet being less likely to be pushed into the case by recoil in the tube during firing?

A crimp on a handgun round does two different things, depending upon whether it is a pistol round fired in an autoloader, or a revolver round fired in a revolver. In the case of your .357 Magnum round, it is to prevent the bullet from easing it's way out of the case due to recoil (and thereby preventing cylinder rotation), and not being pushed into the case by recoil. In the case of a pistol round, it is to prevent the bullet from being pushed into the case when the cartridge makes the transition from the magazine to the chamber. Hope that helps.

Don

 

[forestswin]

based on your example.....the key issue is that its a tube fed lever action
recoil will cause the ammo in the tube to smack into each other - case head to bullet tip

crimping is not optional for tube fed magazines

before you seat a bullet - you are expanding the case - you won't get enough bullet hold to counter these "smacking" forces by just removing the flare

roll crimps into a crimp groove or cannelures is whats needed for safety

 

[Rule3]

based on your example.....the key issue is that its a tube fed lever action
recoil will cause the ammo in the tube to smack into each other - case head to bullet tip

crimping is not optional for tube fed magazines

before you seat a bullet - you are expanding the case - you won't get enough bullet hold to counter these "smacking" forces by just removing the flare

roll crimps into a crimp groove or cannelures is whats needed for safety

Yep.
and for the OP, what type of bullet are you using in a lever action?

 

[buck460XVR]

Post #4 and #6 sum it up quite nicely and since it's a handgun caliber lever gun, both apply.

 

[Rule3]

Semi auto and revolvers really have no relevance to the OPs question. It is a tube fed lever action rifle.

For the OPs question of:
"Absolutely every other thing being equal, what does a crimp do?"

Post #6.

Bottom line it keeps the bullet from sinking into the case, raising pressure and blowing up the rifle.

 

[ArchAngelCD]

Semi auto and revolvers really have no relevance to the OPs question. It is a tube fed lever action rifle.

For the OPs question of:
"Absolutely every other thing being equal, what does a crimp do?"

Post #6.

Bottom line it keeps the bullet from sinking into the case, raising pressure and blowing up the rifle.

Exactly. You don't want the pressures being raised and destroying your gun.

 

[Demi-human]

In an auto, the bullets smack the front of the magazine. Resulting in the possibility of setback.

In a lever action, the bullets smack into each other inside the magazine. Resulting in the possibility of setback.

Not exactly unrelated.

I will grant that revolvers do not setback, they " jump crimp" and bind the cylinder.