TBeck's on the right track here, but there is a lot more to it. Velocity is a major factor in the .223's makup and has to be considered prominantly when figuring penetration. As the bullet slows down, it will penetrate less. The mass and makeup of the bullet is also important. We all know that a solid round is less likely to breakup and will penetrate more than a frangible round. (12 gauge slug vs. #9 shot at same velocity) Likewise mass is equally important when figuring out energy. (heavy bullets penetrate farther than lighter ones, everything else being equal) But when both mass and velocity are taken together it is still energy transfer that is the crux of the "urban rifle" arguement. Energy has to be enough to perform adequately, but should drop off quickly enough that it is fairly harmless after penetrating an "urban" wall.
Energy is figured by multiplying mass X velocity squared then divided by 450436. The .223 uses a bullet with small mass. (55gr standard) Most of its energy comes from velocity. (2900-3200 fps) This is plenty of energy to take out BGs, but scary because of what it will do to walls, cars and such that also get shot. A cinder block wall is only cover for the first couple of rounds, then it is only rubble.
When the round hits something, mass is lost through fracturing and deformation, velocity is lost through friction. When the round hits something that soaks up velocity (kevlar, wood, flesh etc.) it slows down and stops in about 13 inches (give or take a few depending on just what was hit, makeup of bullet, and actual velocity) because its speed is lost before bullet mass. When it hits something harder (steel plates, concrete, rocks, etc.) the bullet mass is lost first, but the speed is substantial enough that even plate steel (unless hardened) will still be cratered.
All this is why the .223, when used with proper velocity and bullets, will puncture Kevlar, four or five inches of hardwood, or car doors, yet won't harm the baby held in your neighbors arms because it passed through a couple sheet rock walls. (maybe)
There is no certainty that a round won't penetrate farther than planned, but most LE departments use the .223 because it is the closest in this respect. I have heard that some big cities are arming SWAT teams with AR-15s with .22lr conversions and firing 30 gr hyper-velocity ammunition to extend this effect. We aren't going to this because of the lack of flexibility. Flexibility is what makes the .223 better, at least IMHO.
Art said it best: There ain't no magic. In a firefight all rules are pretty much off, but it is up to each person (or LE entity) to take as much as possible into consideration when equiping for defense. All this comes under the heading: Remember proper firearm safety rules and always be sure of your target and what's beyond. Luck to all.
Edit - oops, forgot to mention that yes, I've done extensive testing of this round. (and others) My testing involved hundreds of rounds from various ammunition manufacturers, bullet types, target media, and conditions. (not simply shooting a few boards and saying - yup, it went through, too much penetration) There is a lot out there and I still try different combinations looking for a little advantage over what I have now. Results: The the .223 isn't perfect and will over penetrate for some senarios and will not penetrate enough for others. It is, however, the closest chambering available (that I've tried) to being able to do it all.
[This message has been edited by yorec (edited August 20, 2000).]
[This message has been edited by yorec (edited August 20, 2000).]
Energy is figured by multiplying mass X velocity squared then divided by 450436. The .223 uses a bullet with small mass. (55gr standard) Most of its energy comes from velocity. (2900-3200 fps) This is plenty of energy to take out BGs, but scary because of what it will do to walls, cars and such that also get shot. A cinder block wall is only cover for the first couple of rounds, then it is only rubble.
When the round hits something, mass is lost through fracturing and deformation, velocity is lost through friction. When the round hits something that soaks up velocity (kevlar, wood, flesh etc.) it slows down and stops in about 13 inches (give or take a few depending on just what was hit, makeup of bullet, and actual velocity) because its speed is lost before bullet mass. When it hits something harder (steel plates, concrete, rocks, etc.) the bullet mass is lost first, but the speed is substantial enough that even plate steel (unless hardened) will still be cratered.
All this is why the .223, when used with proper velocity and bullets, will puncture Kevlar, four or five inches of hardwood, or car doors, yet won't harm the baby held in your neighbors arms because it passed through a couple sheet rock walls. (maybe)
There is no certainty that a round won't penetrate farther than planned, but most LE departments use the .223 because it is the closest in this respect. I have heard that some big cities are arming SWAT teams with AR-15s with .22lr conversions and firing 30 gr hyper-velocity ammunition to extend this effect. We aren't going to this because of the lack of flexibility. Flexibility is what makes the .223 better, at least IMHO.
Art said it best: There ain't no magic. In a firefight all rules are pretty much off, but it is up to each person (or LE entity) to take as much as possible into consideration when equiping for defense. All this comes under the heading: Remember proper firearm safety rules and always be sure of your target and what's beyond. Luck to all.
Edit - oops, forgot to mention that yes, I've done extensive testing of this round. (and others) My testing involved hundreds of rounds from various ammunition manufacturers, bullet types, target media, and conditions. (not simply shooting a few boards and saying - yup, it went through, too much penetration) There is a lot out there and I still try different combinations looking for a little advantage over what I have now. Results: The the .223 isn't perfect and will over penetrate for some senarios and will not penetrate enough for others. It is, however, the closest chambering available (that I've tried) to being able to do it all.
[This message has been edited by yorec (edited August 20, 2000).]
[This message has been edited by yorec (edited August 20, 2000).]
, Art