Why do the Russian rounds have so much more penetration?

[SnakeLogan]

Just a question for those of you who know more about bullets than I do.



As I've said before, I'm curious to see how much penetration a 6.8 SPC fmj would get in gel. Wonder if it'd be more like a 223 fmj or a 7.62x39 fmj.

 

[Shear_stress]

There are a few reasons that relate to bullet construction, weight, and velocity. One of them is that the non-AP 5.56 tends to fragment at the cannelure while the 5.45x39 is designed to tumble (copying what was thought at the time to be the 5.56's main wounding mechanism). The 7.62x39 uses a much larger bullet than either of the other rounds and is driven at a lower velocity. These allow it to retain more weight (having a steel core helps too).

 

[Archie]

Rather simplified...

Penetration in a homologous mass is a function of momentum. Typically heavier bullets tend to penetrate more, other factors being roughly equal. "Heavier" can also mean 'staying together and maintaining more weight in one piece' in the case of bullets.

A second consideration is sectional density; or the weight to diameter ratio. (Think icepick versus ball peen hammer; the icepick penetrates better.)

By way of contrast, penetration in a single thickness barrier (including car doors and bullet proof vests) is a function of velocity at time of impact. Faster be better.

 

[SnakeLogan]

So how would you guys expect 6.8 SPC fmj to perform? Would it fragment like 223 or stay together like 30 carbine and 7.62x39?

 

[kcmarine]

delete please... look below.

 

[kcmarine]

Dirty Joke Warning: Do Not highlight the text below if you are easily offended...

It seems like Russian rifle rounds are much like drunken Russian men... sure, they can penetrate, but can't do very much when they get inside.

*End of dirty joke*

Anyways, yeah... the guys above explained it well. Russian rounds are heavier. When a round is heavier, it carries more momentum. More momentum means that a round carries its energy for a longer distance through the medium it is fired at. A negative side effect of this is that these projectiles are less likely to disperse their carried energy into the target at the appropriate depth, thus reducing the chance of a lethal wound when compared to a lighter round like the 5.56x45mm. Bullet design is really a world of trade offs... you trade increased penetration for energy dispersion. More recently developed rounds like the 6.8x43mm and the 6.5 Beowulf are beginning to find the balance between the two extremes.