What does "fragmentation threshold" mean?

[M4Fundi]

What does "fragmentation threshold" mean?

[thopkins22]

The velocity above which the bullet design will reliably fragment.

ETA: Died laughing at Todd and Mark's responses.

[ToddG]

fragmentation threshold: The point at which a terminal ballistics debate gets so ridiculous that your head explodes.

[markm]

fragmentation threshold: The point at which a terminal ballistics debate gets so ridiculous that your head explodes.

Inverse proportion: The more a person is concerned about bullet frag, the less likely he is ever going to use a rifle for defensive purposes.

Direct proportion: The more a person is concerned about bullet frag, the more likely he is to lock his AR up and grab a bird gun for home defense!

[M4Fundi]

So it is a terminal ballistics term or exterior ballistics term?

It means the bullet is traveling TOO fast to reliably fragment? How does that work?

[markm]

I think it means the point where a rifle bullet is going too slow to frag. At least that's the most common debate I see.

[rob_s]

Yes, it's the minimum velocity above which the projectile will perform as designed (in this case, fragment). Can be used for calculating the related term "effective range".

[M4Fundi]

Thanks, I guess it was the "above" which confused me.

Would it be correct to say that the Fragmentation Threshold is the lowest velocity (and above or just lowest velocity?) that a bullet will expand, fragment and perform as it was designed to perform? So, the Fragmentation Threshold is a fixed speed or speed and all speeds it is capable of and above?

Forgive me but I keep a training manual in progress and as I was taught eons ago if you can't put it into writing then you don't really know it, so I'm trying to complete some sections on ballistics and am working on proper explanations and glossary.

[Molon]

Fragmentation and expansion are two different things. Other than that, you have the basic idea. At velocities below the fragmentation threshold, the bullet will not reliably fragment or it may not even fragment at all. At velocities equal to or above the fragmentation threshold, the bullet should reliably fragment. Note I said “should” reliably fragment. None of this is a guarantee as there are a lot of variables involved.

For example, M855 will fragment approximately 75% of the time at a velocity of around 2600 fps. Approximately 25% of the time it will have no significant fragmentation at 2600 fps. A 25% failure to fragment is not considered “reliable” fragmentation. The accepted fragmentation threshold for M855 is therefore at a higher velocity than 2600 fps; it’s generally accepted to be approximately 2700 fps.

Other issues come into play as well. “Fleet yaw” for example may result in a bullet not fragmenting even though its velocity is above the fragmentation threshold. Approximately 15% of the time M193 will travel up to 20 cm before yawing and fragmenting. If the receiving end of an M193 round were say a malnourished “Skinny”, the bullet could practically sail right through his torso before fragmenting. M855 has similar problems.




Courtesy of Dr. Martin Fackler

[M4Fundi]

Thanks for the great info and photos!