Dented ammo question

[SomeOtherGuy]

I think it is more of an issue with handguns than bottle neck rifle cartridges. It is sort of creating additional free bore.

I think the issue is really case capacity, burn rate, and intended peak pressure. Setback is very dangerous when the case is small, already full, and on the edge of pressure issues - 40 S&W, 357 SIG, 5.7x28 FN. Much less of an issue for larger cases, often from older cartridges like .30-06, .357 Mag, etc. The issue is whether a dangerous pressure will develop in the confined space before the bullet starts moving. Supposedly 5.7x28 is crazy dangerous for this, to the extent that reloading is not recommended and has extra warnings in load manuals.

[The_War_Wagon]

I say shoot it.

But don't take it to a carbine course (ask me how I know ).

[Ron3]

I think the issue is really case capacity, burn rate, and intended peak pressure. Setback is very dangerous when the case is small, already full, and on the edge of pressure issues - 40 S&W, 357 SIG, 5.7x28 FN. Much less of an issue for larger cases, often from older cartridges like .30-06, .357 Mag, etc. The issue is whether a dangerous pressure will develop in the confined space before the bullet starts moving. Supposedly 5.7x28 is crazy dangerous for this, to the extent that reloading is not recommended and has extra warnings in load manuals.

How about .25 acp? 😁

I was trying to get 55 gr LFN bullets to work but they had to sit too deep in the case. IIRC I had a couple chrono just over 900 fps. Probably too hot. I think that was 1.1 grs of 700x.

[utahjeepr]

I think the issue is really case capacity, burn rate, and intended peak pressure. Setback is very dangerous when the case is small, already full, and on the edge of pressure issues - 40 S&W, 357 SIG, 5.7x28 FN. Much less of an issue for larger cases, often from older cartridges like .30-06, .357 Mag, etc. The issue is whether a dangerous pressure will develop in the confined space before the bullet starts moving. Supposedly 5.7x28 is crazy dangerous for this, to the extent that reloading is not recommended and has extra warnings in load manuals.

Ok, somebody school me like I'm 5. You have an essentially unrestrained bullet stuffed in a little too far, wouldn't pressure simply push the bullet out. I'm sure there is some sort of dynamic I'm not understanding but I mean, there's a pressure relief valve right there. In the form of a barrel and a bullet. I can understand overloading beyond what the chamber can withstand or that cannot be relieved quickly enough to prevent a kaboom. But this doesn't sound like it should be an issue to me. The bullet shouldn't even have the resistance of the bore until it jumps the equivalent of the setback.

I am just not educated enough on the combustion dynamics to understand why this would be a problem

[SomeOtherGuy]

Ok, somebody school me like I'm 5. You have an essentially unrestrained bullet stuffed in a little too far, wouldn't pressure simply push the bullet out. I'm sure there is some sort of dynamic I'm not understanding but I mean, there's a pressure relief valve right there. In the form of a barrel and a bullet. I can understand overloading beyond what the chamber can withstand or that cannot be relieved quickly enough to prevent a kaboom. But this doesn't sound like it should be an issue to me. The bullet shouldn't even have the resistance of the bore until it jumps the equivalent of the setback.

I am just not educated enough on the combustion dynamics to understand why this would be a problem

I'll try, but maybe an engineer or industry type can do better.

All propellants have an inherent burn rate. Most have an increasing burn rate as temperature and pressure increase. Inside a case there is total confinement on all sides except the bullet, which provides limited confinement due to its mass and resulting inertia. The bullet also has a slight "stiction" to overcome before it starts moving - that depends on crimping, and if you jam a bullet into the lands (which would be a longer OAL than normal) it gets worse.

Primer ignites, propellant all ignites as a result. The propellant creates a certain volume of gas based on its quantity, burn rate, and how good the primer's ignition was. This initial volume of gas starts moving the bullet, and also accelerates the burn rate of remaining propellant. But the bullet doesn't move instantly, and its initial movement is, relatively speaking, slow.

Let's say you have 8 grains of propellant in a .40 S&W case, bullet properly seated. It reaches 35k psi, which is OK. Let's say you seat the bullet too deep and there's only 90% of the intended volume. Pressure reaches 110% or 38.5k psi, which is over pressure but probably won't break anything. Except propellant burn rate increases with pressure, so in fact having 90% of intended volume might create 120% of intended pressure. That's near a proof load. Go to 80% volume, maybe you get 140% intended pressure, things start breaking.

Not an expert but that's my understanding.

[markm]

Let's say you seat the bullet too deep and there's only 90% of the intended volume. Pressure reaches 110% or 38.5k psi, which is over pressure but probably won't break anything.

Un-expert follow up to this.. creating a little bullet "jump" to the lands allows some pressure bleed off before the bullet seats in the barrel. As I understand it, this is a part of the dimensions of the 5.56mm chamber that allow for more pressure than .223 SAAMI.

I get that pistol and rifle rounds aren't apples to apples, but there you go..

(I'm not advocating for set back, just saying it's not the instant doom scenario that it might seem)

[Bret]

I've never worried about a light or mild dent in a brass case.

Recently someone told me more than a very slight dent in the neck of the brass (5.56) was dangerous.

I disagreed stating the brass will fire-form to the chamber and there is nothing dangerous about it.

What say you?

I say that I need more information. If you're talking about a case with a dented neck before it's loaded, then the sizing step should remove the dent. If there's still a dent after you size the case, then you should toss it. It may fire, but reliability and accuracy should also be a concern.

If you're talking about a loaded cartridge that somehow has dented case neck, then I'd wonder what happened. I can't ever recall seeing a loaded cartridge with noticeably dented case neck. I've seen them with bent case necks causes buy misfeeds, but not really dented. As ViniVidivici pointed out, if it plunks in and out of the chamber, then it's fine. If it won't, then toss it not just for safety reasons, but for reliability and accuracy.

[markm]

I can't ever recall seeing a loaded cartridge with noticeably dented case neck.

It can happen if a guy overdoes it on case lube. It hydraulics a dent in the shoulder usually.

[mRad]

It can happen if a guy overdoes it on case lube. It hydraulics a dent in the shoulder usually.

Or too much shoulder set-back.


Sent from my iPhone using Tapatalk

[Bret]

It can happen if a guy overdoes it on case lube. It hydraulics a dent in the shoulder usually.

I've done that myself, but he's talking about the neck.