Lethality of 5.56mm round after penetrating body armor?

[Skyfire1201]

I'm new to terminal ballistics, and have been reading the various posts on this forum. One question the various hard/soft body armor test/review articles doesn't seem to answer, is what is the terminal ballistics of M855 or M193 round after it has penetrated body armor. I think it's reasonable to assme the body armor will absorb some of the bullet's energy during penetration, does that mean a M855 round, after penetrating a Level IV plate and enters tissue, it'll more or less behave like .22LR in terms of penetration and fragmentation? (which is to say, none at all)

[WS6]

I'm new to terminal ballistics, and have been reading the various posts on this forum. One question the various hard/soft body armor test/review articles doesn't seem to answer, is what is the terminal ballistics of M855 or M193 round after it has penetrated body armor. I think it's reasonable to assme the body armor will absorb some of the bullet's energy during penetration, does that mean a M855 round, after penetrating a Level IV plate and enters tissue, it'll more or less behave like .22LR in terms of penetration and fragmentation? (which is to say, none at all)

An M855 round won't make it through IV Plate to begin with from what I understand.

[Ironman8]

If you're talking about a brand new, quality level 4 plate, then that M855 round isn't penetrating regardless.

If you're talking about a plate that is cracked/already shot, and the round happens to find that crack, then the wound will depend on how much of the plate the round came in contact with before entering your body. I know I would much rather have a cracked/shot plate than no plate at all...

[DocGKR]

As noted above, properly designed Level III and Level IV plates will defeat M193 and M855 so there is no penetration. When these projectiles penetrate LIIIa armor, they offer terminal performance almost identical to shots without any armor.

[Skyfire1201]

As noted above, properly designed Level III and Level IV plates will defeat M193 and M855 so there is no penetration. When these projectiles penetrate LIIIa armor, they offer terminal performance almost identical to shots without any armor.

LIIIa armor won't even slow down the round one bit? I would think the bullet would use up a lot of its energy in order to penetrate the plate, thus entering tissue at much slower velocity.

[WS6]

LIIIa armor won't even slow down the round one bit? I would think the bullet would use up a lot of its energy in order to penetrate the plate, thus entering tissue at much slower velocity.

3a has no plate. The round will ice pick through it very easily, then yaw and fragment as normal.

[Grytpype]

As noted above, properly designed Level III and Level IV plates will defeat M193 and M855 so there is no penetration. When these projectiles penetrate LIIIa armor, they offer terminal performance almost identical to shots without any armor.

Don't they enter their yaw cycle much earlier after penetrating armor? ISTR reading an article about that, but it's been years.

[DocGKR]

Nope, 5.56 mm pretty much zips through IIIa like it is not there. Now, the projectile will begin to yaw and upset much earlier if it first goes through a full water bladder (like a Camelback), prior to entering tissue, but that is a different subject...

[Aries144]

Just for clarity's sake:

level IIIa is fabric/soft laminates- no plate at all

level III is a hard plate

level IV is a hard plate

M855 will not penetrate either level III or level IV armor (plates).

Almost every center-fire rifle round will penetrate level IIIa armor (fabric/soft laminate) like it isn't even there.

[tpd223]

Just for clarity's sake:

level IIIa is fabric/soft laminates- no plate at all

level III is a hard plate

level IV is a hard plate

M855 will not penetrate either level III or level IV armor (plates).

Almost every center-fire rifle round will penetrate level IIIa armor (fabric/soft laminate) like it isn't even there.

For the most part, yes.

However, comma,,,

Some common 5.56 rounds will penetrate some of the various level III plates on the market, Doc has written about this previously in his testing write-ups.