I bought a pack of 100 Winchester 9mm ammo.  The bullet of one of the rounds is seated very noticably lower than the others.  Could that be a problem?  I don't have a ruler handy, but it's about 3mm farther in the shell than the others.

Edited:  A better way to describe it is when I put it and a normal round on a table bullet-down, the rim of the questionable round is level with where the  rim groove of the other round stops.  I don't know the terminology, but I suppose you get the idea.

Quoted: I bought a pack of 100 Winchester 9mm ammo.  The bullet of one of the rounds is seated very noticably lower than the others.  Could that be a problem?  I don't have a ruler handy, but it's about 3mm farther in the shell than the others.

could pose a pressure problem.

if in doubt, toss it out, or pull the bullet and reuse the brass for reloading

could cause a feed problem.  don't know about other problems, but i'm sure somone will be along soon to help.

i wonder if you could fire a .380 round through a 9mm gun?  it's the same diameter, just shorter

Quoted: I bought a pack of 100 Winchester 9mm ammo.  The bullet of one of the rounds is seated very noticably lower than the others.  Could that be a problem?  I don't have a ruler handy, but it's about 3mm farther in the shell than the others. Edited:  A better way to describe it is when I put it and a normal round on a table bullet-down, the rim of the questionable round is level with where the  rim groove of the other round stops.  I don't know the terminology, but I suppose you get the idea.

3mm may not look like a lot when you're eye-balling it, but that is enough to produce tremendous chamber pressures.  Given that a lot of 9mm's don't have fully supported chambers, I wouldn't shoot it.  I'd also let Winchester know about this, their QC people need to be on the lookout for more of these.

CO

I read a long time ago, that seating a bullet too deep can double pressures in some cartridges, especially 9mm.
This was from a Speer reloading manual that I haven't seen in years. It was in the section on straight-walled rimless cartridges, because that type of cartridge head-spaces on the mouth and only a tapered crimp can be used. The concern was that if the crimp wasn't tight enough the forces of slide action during firing could force loosely held bullets of rounds remaining in the mag, to seat deeper, causing a potentially serious over-pressure situation.

What everyone else is saying is true. Do not fire it. The pressure could potentially be explosively high. (It’s likely the bullet is actually compressing the powder charge.) Odds are nothing bad will happen if you did fire it, but a 25-cent cartridge isn’t worth the potential loss of a pistol, and a few body parts.

Many years ago I was at the range with a friend. The clerk gave him .380s instead of 9mm ammo for his P-38. He thought something was wrong with the pistol when it wouldn’t cycle. I came over to check and noticed the ammo problem.

The rounds did fire, but obviously wouldn’t cycle the pistol. He only fired a few shots and I never tried to repeat his impromptu experiment. But in an emergency I suppose .380s could be shot from a 9mm. But you would have a low powered single shot pistol.

That can be problem as pressure will be higher.

How much higer?  An old rule of thumb from years ago was that with same powder charge, 5% decrease in case capacity will increase pressure by 10% and 5% increase in case capacity will decrease pressure by 10%.  This is not scientifically accurate but has a lot of truth to it.  Despite the increase or decrease in pressure the velocity of the bullet will remain pretty consistant as velocity is more dependent on the powder charge than pressure.

This is how (increase the OAL) you get Ruger 45Colt revolvers to shoot 320gr cast bullets to 1,300 fps without blowing up the cylinder... well, this and few other tricks.

Is one bullet worth your gun or your saftey? Toss it out if in question...

Quoted: YES a minor setback can cause a great deal of pressure increase in the case. depending on the load it could lead to a failure of the case and destruction of your gun. if you are unsure, dispose of it.

There it is. That's the answer to your question. Toss it.

(I've been drinking too much to let a simple "+1" do.)

WWB is cheap, but you have to look at each round when loading it, as their QC isn't as good- that's the price you pay.

I look at EVERY round I load into a mag.  I've had some pretty scary 9mm and Lake City XM-193.  Here's a WWB round I notice a month back when loading mags.

ED_P,

Those are purposefully put in so you can practice failure to feed drills.

Quoted: ED_P, Those are purposefully put in so you can practice failure to feed drills.

I did not know that-  I'll make sure not to toss them in the future...