I saw this on LiveJournal, posted by user "longarm", and thought of how useful this would be for reference. I've included the comments and clarifications.
<hr>
Advanced Pistol 2: Rapid Deployment Pistol Operator
This is an after class write up completed by the Instructor.

We just finished the Advanced Pistol 2: Rapid Deployment Pistol Operator course at the Harvey Police Department range and had another outstanding class. The class started in the morning with a short lecture on rapid deployment concepts and then addressed Department of Homeland Security training issues and preparation for potential terrorist attacks on U.S. soil. Emphasis on the use of aggressive decisive action to engage terrorists and militant Muslim extremists during a rapid deployment incident was driven home.

We then moved to the range and after a short "warm-up", students skills were put to the test with moving off the line of force drills and multi-task drills during continuous movement around various obstacles. Multiple no shoot targets were incorporated in the drills with students gradually moving to engage multiple threats while negotiating around multiple no-shoot targets and maintaining continuous movement. All ammunition management, threat assessment and 360-degree area scanning was done on the move!

After a short lunch, we returned to the range and began continuous lateral movement drills. Students would move laterally from the left side of the range to the right side of the range engaging multiple threats while negotiating various obstacles and A LOT of no-shoot targets!

This was followed up by rapid movement drills while engaging multiple threats that familiarized students with engaging threats during several speeds of movement; covert speed (cautious movement speed), warrant service speed (directed movement speed) and hostage rescue speed (rapid movement - running).

The same techniques were applied again when students participated in the in-line CQB course and staggered threat CQB course using the same speed concepts.

After a short break, it was off to ballistic testing on vehicle windshield glass and vehicle sheet metal. Over 12 students brought in various types of handgun, rifle and shotgun duty ammunition that was tested and evaluated on the vehicle donated for testing.

Testing started with the lead instructor (John Krup

a) sitting in the vehicle and demonstrating ballistic capabilities and performance of handgun duty ammunition fired through the windshield from inside the vehicle! An awesome test that exposed students to a practical concept that could be used should an officer be engaged in a vehicle and is unable to immediately egress the vehicle.

Once all duty handgun ammunition was tested from inside the vehicle, the same test was conducted from outside the vehicle shooting through windshield glass into the vehicle. Surprisingly, in both tests, almost all duty ammunition in all calibers tested, 9mm, .40 S&W, .45 acp and .357 magnum experienced jacket separation and slight angle deflection due to the angle of the windshield. The 124 gr Gold Dot worked most consistently and did not display jacket separation. All duty handgun rounds displayed inconsistent and poor penetration capabilities when fired into the engine block and doors of the vehicle. The engine block stopped all handgun rounds and most handgun rounds entered the doors, but failed to exit into the interior of the vehicle.

On to rifles. Testing started with .30 caliber carbine which displayed excellent penetration through windshield glass and consistently penetrated sheet metal on the car doors into the interior of the vehicle. Engine block stopped all .30 cal. rounds. Next, we used an
M-1 Garand in .30-06. Clean through the windshield, interior of the vehicle and out the back of the trunk. Consistently penetrated the sheet metal on the car doors entering through one door, moving through the interior of the vehicle and exiting the door on the opposite side of the vehicle. Impressive!!! The engine block was shot with 16 rounds of black tip armor piercing ammunition and all rounds were stopped by the engine block!

Next was 7.62 x 39 ammunition fired from a Krebs Custom KTR-03S. The results were almost identical to the performance of the
.30-06 rounds. 5.56 ball and Federal Tactical (fired from a Rock River LAR-15) penetrated windshield glass with no problem and consistently penetrated vehicle sheet metal entering the interior of the vehicle, but in most cases, were stopped by sheet metal on the opposite side of the vehicle. All 5.56 (ball, Federal Tactical and SS109) were all stopped by the engine block.

We finished up with 12 gauge #00 buckshot and slug. #00 through the windshield performed excellent, straight on, however, any oblique angles involved resulted in pellet deflection. All #00 was stopped by vehicle sheet metal! Slug was another story. Slug penetrated sheet metal consistently with an occasional stop in the doors where extra metal existed. All slugs were stopped by the engine block.

After another exhausting day of training, we called it quits and cleaned the range up. Class closing lecture and discussion focused on an increased likelihood of seeing attacks such as what occurred in England, Russia and Spain coming ever closer to the shores of the U.S. It was made quite clear that we must remain ever vigilant if we are going to win the war on terrorism.

It was also interesting for students to learn and have confidence that their duty ammunition can be fired through windshield glass from inside the vehicle and out. It was also assuring to know that the safest place you can be when using a vehicle for cover is behind the engine block and front axle.

Thanks for listening. Stay safe, and I'll see you on the range!

Respectfully,

John Krupa III
President
Spartan Tactical Training Group, Inc.
<hr>
[info]ilcylic
2005-07-11 00:08 (link)
That's odd. I've used #00 Buck that went right through heavy 1970's automobile sheet metal.

-Ogre

<hr>

[info]no_brakes23
2005-07-11 05:21 (link)
So the engine block stops everything?

It also sounds like 5.56 is a good round to minimize collateral damage because it penetrates, but does not over penetrate as much as the larger rounds.

Just out of curiousity, not as a matter of practicality, I wonder how .50BMG would do against the engine block. I would have thought the slug or '06 might have penetrated.

Any data on radiator damage?

<HR>

[info]longarm
2005-07-11 09:33 (link)
50 BMG would have been nice to see.

If I remember correctly a handgun round punctured the radiator and caused all the fluids to drain.

<HR>

[info]no_brakes23
2005-07-11 09:43 (link)
So this would indicate that there is no immediate tactical benefit to firing to "disable" the vehicle? (Obviously no radiator will eventually disable the vehicle.)

Also is there any reason .308/7.62x51 wasn't tested? Or was it assumed that it would perform close to the '06?

<HR>

[info]longarm
2005-07-11 09:56 (link)
No body brought a .308. It wasn't a scientific test. Just bring what ya brought and lets see what it does.

<HR>

[info]no_brakes23
2005-07-11 10:31 (link)
Ahhh, I have fallen prey to the assumption that .308 is ubiquitous amongst Mil/LEO types.

(Which I shouldn't, since I don't even own one.)

<HR>

[info]longarm
2005-07-11 21:43 (link)
Our snipers have .308 but not normal patrol

<HR>

[info]ilcylic
2005-07-11 11:50 (link)
So, when you say "stopped by the engine block" do you mean "did not enter the engine block" or "stopped somewhere inside the engine block"?

-Ogre

<HR>

[info]longarm
2005-07-11 21:42 (link)
stopped somewhere inside

<HR>

[info]trb_1911
2005-07-12 14:55 (link)
The typical engine block as a 500 pound hunk of cast iron. Not the most resilient material, perhaps a bit brittle, but they tend to stop bullets pretty well. Modern aluminum engine blocks would be more fragile, but it's still a hunk of metal the size of a human torso, if not larger. I wouldn't be disappointed by the failure of a handgun or rifle round to do significant damage.

Now, car sheet metal, though, vexes me. I have an '87 Pontiac Sunbird in my backyard I got for $10 after its owner defaulted it to the gas station a friend of mine was working at. It is now in my backyard, and serves as my testbed when I feel the need to experiment with such things. The doors are remarkably hard to penetrate, not sue to the sheet metal, but due to things inside, like the window regulators, various reinforcing stringers, and then the thickness of the upholstered door panel and armrest. You have to avoid most of that internal mess and aim high or low enough that the armrest isn't struck, in order to get a .45 FMJ into the interior. It's easier to just get the glass. Bullets fired through the trunk lid exit into the interior through the backseat about 50% of the time, but with no appreciable accuracy or stability. Firing through the roof is 100% effective. Three bullets and a hard side kick (wear boots and long pants!) will eliminate any window on the car, and the kick isn't always necessary.

I saw this on LiveJournal, posted by user "longarm", and thought of how useful this would be for reference. I've included the comments and clarifications.
<hr>
Advanced Pistol 2: Rapid Deployment Pistol Operator
This is an after class write up completed by the Instructor.

We just finished the Advanced Pistol 2: Rapid Deployment Pistol Operator course at the Harvey Police Department range and had another outstanding class. The class started in the morning with a short lecture on rapid deployment concepts and then addressed Department of Homeland Security training issues and preparation for potential terrorist attacks on U.S. soil. Emphasis on the use of aggressive decisive action to engage terrorists and militant Muslim extremists during a rapid deployment incident was driven home.

We then moved to the range and after a short "warm-up", students skills were put to the test with moving off the line of force drills and multi-task drills during continuous movement around various obstacles. Multiple no shoot targets were incorporated in the drills with students gradually moving to engage multiple threats while negotiating around multiple no-shoot targets and maintaining continuous movement. All ammunition management, threat assessment and 360-degree area scanning was done on the move!

After a short lunch, we returned to the range and began continuous lateral movement drills. Students would move laterally from the left side of the range to the right side of the range engaging multiple threats while negotiating various obstacles and A LOT of no-shoot targets!

This was followed up by rapid movement drills while engaging multiple threats that familiarized students with engaging threats during several speeds of movement; covert speed (cautious movement speed), warrant service speed (directed movement speed) and hostage rescue speed (rapid movement - running).

The same techniques were applied again when students participated in the in-line CQB course and staggered threat CQB course using the same speed concepts.

After a short break, it was off to ballistic testing on vehicle windshield glass and vehicle sheet metal. Over 12 students brought in various types of handgun, rifle and shotgun duty ammunition that was tested and evaluated on the vehicle donated for testing.

Testing started with the lead instructor (John Krup

a) sitting in the vehicle and demonstrating ballistic capabilities and performance of handgun duty ammunition fired through the windshield from inside the vehicle! An awesome test that exposed students to a practical concept that could be used should an officer be engaged in a vehicle and is unable to immediately egress the vehicle.

Once all duty handgun ammunition was tested from inside the vehicle, the same test was conducted from outside the vehicle shooting through windshield glass into the vehicle. Surprisingly, in both tests, almost all duty ammunition in all calibers tested, 9mm, .40 S&W, .45 acp and .357 magnum experienced jacket separation and slight angle deflection due to the angle of the windshield. The 124 gr Gold Dot worked most consistently and did not display jacket separation. All duty handgun rounds displayed inconsistent and poor penetration capabilities when fired into the engine block and doors of the vehicle. The engine block stopped all handgun rounds and most handgun rounds entered the doors, but failed to exit into the interior of the vehicle.

On to rifles. Testing started with .30 caliber carbine which displayed excellent penetration through windshield glass and consistently penetrated sheet metal on the car doors into the interior of the vehicle. Engine block stopped all .30 cal. rounds. Next, we used an
M-1 Garand in .30-06. Clean through the windshield, interior of the vehicle and out the back of the trunk. Consistently penetrated the sheet metal on the car doors entering through one door, moving through the interior of the vehicle and exiting the door on the opposite side of the vehicle. Impressive!!! The engine block was shot with 16 rounds of black tip armor piercing ammunition and all rounds were stopped by the engine block!

Next was 7.62 x 39 ammunition fired from a Krebs Custom KTR-03S. The results were almost identical to the performance of the
.30-06 rounds. 5.56 ball and Federal Tactical (fired from a Rock River LAR-15) penetrated windshield glass with no problem and consistently penetrated vehicle sheet metal entering the interior of the vehicle, but in most cases, were stopped by sheet metal on the opposite side of the vehicle. All 5.56 (ball, Federal Tactical and SS109) were all stopped by the engine block.

We finished up with 12 gauge #00 buckshot and slug. #00 through the windshield performed excellent, straight on, however, any oblique angles involved resulted in pellet deflection. All #00 was stopped by vehicle sheet metal! Slug was another story. Slug penetrated sheet metal consistently with an occasional stop in the doors where extra metal existed. All slugs were stopped by the engine block.

After another exhausting day of training, we called it quits and cleaned the range up. Class closing lecture and discussion focused on an increased likelihood of seeing attacks such as what occurred in England, Russia and Spain coming ever closer to the shores of the U.S. It was made quite clear that we must remain ever vigilant if we are going to win the war on terrorism.

It was also interesting for students to learn and have confidence that their duty ammunition can be fired through windshield glass from inside the vehicle and out. It was also assuring to know that the safest place you can be when using a vehicle for cover is behind the engine block and front axle.

Thanks for listening. Stay safe, and I'll see you on the range!

Respectfully,

John Krupa III
President
Spartan Tactical Training Group, Inc.
<hr>
[info]ilcylic
2005-07-11 00:08 (link)
That's odd. I've used #00 Buck that went right through heavy 1970's automobile sheet metal.

-Ogre

<hr>

[info]no_brakes23
2005-07-11 05:21 (link)
So the engine block stops everything?

It also sounds like 5.56 is a good round to minimize collateral damage because it penetrates, but does not over penetrate as much as the larger rounds.

Just out of curiousity, not as a matter of practicality, I wonder how .50BMG would do against the engine block. I would have thought the slug or '06 might have penetrated.

Any data on radiator damage?

<HR>

[info]longarm
2005-07-11 09:33 (link)
50 BMG would have been nice to see.

If I remember correctly a handgun round punctured the radiator and caused all the fluids to drain.

<HR>

[info]no_brakes23
2005-07-11 09:43 (link)
So this would indicate that there is no immediate tactical benefit to firing to "disable" the vehicle? (Obviously no radiator will eventually disable the vehicle.)

Also is there any reason .308/7.62x51 wasn't tested? Or was it assumed that it would perform close to the '06?

<HR>

[info]longarm
2005-07-11 09:56 (link)
No body brought a .308. It wasn't a scientific test. Just bring what ya brought and lets see what it does.

<HR>

[info]no_brakes23
2005-07-11 10:31 (link)
Ahhh, I have fallen prey to the assumption that .308 is ubiquitous amongst Mil/LEO types.

(Which I shouldn't, since I don't even own one.)

<HR>

[info]longarm
2005-07-11 21:43 (link)
Our snipers have .308 but not normal patrol

<HR>

[info]ilcylic
2005-07-11 11:50 (link)
So, when you say "stopped by the engine block" do you mean "did not enter the engine block" or "stopped somewhere inside the engine block"?

-Ogre

<HR>

[info]longarm
2005-07-11 21:42 (link)
stopped somewhere inside

<HR>

[info]trb_1911
2005-07-12 14:55 (link)
The typical engine block as a 500 pound hunk of cast iron. Not the most resilient material, perhaps a bit brittle, but they tend to stop bullets pretty well. Modern aluminum engine blocks would be more fragile, but it's still a hunk of metal the size of a human torso, if not larger. I wouldn't be disappointed by the failure of a handgun or rifle round to do significant damage.

Now, car sheet metal, though, vexes me. I have an '87 Pontiac Sunbird in my backyard I got for $10 after its owner defaulted it to the gas station a friend of mine was working at. It is now in my backyard, and serves as my testbed when I feel the need to experiment with such things. The doors are remarkably hard to penetrate, not sue to the sheet metal, but due to things inside, like the window regulators, various reinforcing stringers, and then the thickness of the upholstered door panel and armrest. You have to avoid most of that internal mess and aim high or low enough that the armrest isn't struck, in order to get a .45 FMJ into the interior. It's easier to just get the glass. Bullets fired through the trunk lid exit into the interior through the backseat about 50% of the time, but with no appreciable accuracy or stability. Firing through the roof is 100% effective. Three bullets and a hard side kick (wear boots and long pants!) will eliminate any window on the car, and the kick isn't always necessary.

I did some tests with high-power rifles a few years back on 1/2" mild steel plate at 100yds.

6mm Rem 75gr dented it nicely

30/06 Black-tip AP , with the internal penetrator left a 1/4" hole and hardly slowed down , after shedding the jacket.
30/06 M2 ball went through just fine too.

The .303 British Mk7 ball ammo , with the internal aluminium nose-cone punched through, and left a 1/2'' dia. hole.

None of these make a great case for hiding in a vehicle while being hosed down with anything over pistol calibre, and even then, it could be dodgy.

http://www.theboxotruth.com/docs/thebuickotruth.htm

http://www.theboxotruth.com/docs/buickot7_3.htm

Hope this is useful.

Ah yes, the Box o' Truth. Interesting read, and the lucky git who wrote that page gets to go to Blackwater!

A few comments, though:

1. If you laminate the inside of your car windows, they will be far more bullet resistant to shots from the outside than shots from the inside.

2. If you bulletproof the glass, don't forget to add shielding to the doors and seat backs/front bulkhead, as well as roof and (if you feel it required) floor.

3. If you want to make your concrete cover cinderblocks 1000% tougher, fill them with gravel and cement - not quite concrete, you want more stone than normal, and the cement is there to bind it together. If you want it even tougher still, use a foaming polyurethane foam instead of cement, as that will bind the bits of broken cement together far better, and disipate shockwaves too.

4. When taking cover behind a car, watch how the intelligent attacker blows your feet off, then shoots you some more once you are down. Because if he is prone, mostly he will be looking at your feet!

A relevant picture to the effectiveness of shooting someones feet out from under them.

This was followed up by rapid movement drills while engaging multiple threats that familiarized students with engaging threats during several speeds of movement; covert speed (cautious movement speed), warrant service speed (directed movement speed) and hostage rescue speed (rapid movement - running).

Can you believe people who shoot while moving especially at "rapid movement - running' speed? I'd say I am sorry but I just had to point that little bit out and no I am not questioning the validity of the post.

I have had the pleasure of shooting up some older vehicles. One of my interesting little things I found out was depending on the doors construction and the angle of fire even 5.56 FMJ could be stopped. Newer model cars seem to be alot easier to penetrate through the doors due to the lack of metal in general.

Jack just to note I don't know if adding laminate will do more to the glasses ability to stop a incoming round. Bullets do well through the front windshiled but tend to change direction alot more. Pistol ammo at 30' can change point of impact as much as 2 feet. Once several rounds have hit and shattered the glass this changes.

Very suprised the bodywork stopped buckshot. Some aaa or bb steel shot would have been interesting though.

Very suprised the bodywork stopped buckshot. Some aaa or bb steel shot would have been interesting though.

Probably little to no difference, I will see if the guys on the other forum used steel or not on there test. the 00 buck is pretty much ball 23acp, and I haven't seen ball 32acp go through a car door yet, and we have been shooting some cars recently (no windows).

Just remember though I like to shoot and move, just like the authors above, so we don't know what were talking about.:rolleyes:

Steel shot may be harder, but it has less penetration because it's less dense than lead, and for buckshot, mass has more bearing on penetration than hardness.

To penetrate front or back windshields with non-slug shotgun ammo, one round has to be fired to break the glass, the next round will penetrate through into the passenger compartment.

Steel shot may be harder, but it has less penetration because it's less dense than lead, and for buckshot, mass has more bearing on penetration than hardness.

To penetrate front or back windshields with non-slug shotgun ammo, one round has to be fired to break the glass, the next round will penetrate through into the passenger compartment.

Are we talking shotgun or pistol ammo? Pistol ammo will go through on the very first shot. I honestly haven't tried shotgun on a car window yet, but I can see if we can pull that off.

I would think it abundantly clear that I was talking about shotgun ammunition by using words like 'Steel shot', 'buckshot', and perhaps most confusingly 'non-slug shotgun ammo'. :p

Here's a post by someone on another board that fits into this topic:

I was on the team that tested the armor of the Peace Keeper Armored Car in 1990-91. This was basically a conversion van with roughly 3/8 inch armor steel plate for a body. At a range of 100 meters at an RAF test facility, we fired 7.62X51 ball, 7.62X51 AP, 7.62X39 ball, 7.62X39 AP, 5.56 M193 and SS109, 8MM Mauser and 303 British Mark VII.

Utilizing a Parker-Hale rifle with 1-10 twist, we shot the various 7.62X51 loads into the left side of the vehicle. Ball ammo would penetrate most of the time. AP breezed through like butter, but neither round would go all the way through both sides.

Also on the left side of the vehicle, we fired the 7.62X39 out of a Russian AKM. It took two to three hits with the ball ammo within a 4-6inch radius to defeat the armor plate. The steel core AP performed about the same, but when one got through, it would also put a pretty good dent on the opposite armor plate.

Using an M16A1, we fired the M193 ammo into the right panel of the PK. It took two hits with the same 4-6 inch radius to pierce the armor. A single hit would penetrate about 75% of the armor plate.

Using an M16A2 and SS109, on the right side panel, the bullets easily poked right through the armor and penetrated roughly 50% of the opposing panel.

Using another Parker-Hale rifle in 8mm Mauser with 1-12 twist, we fired into the left rear door. We were using Portuguese heavy ball. The bullets put a dent in the armor, but just bounced right back at us.

With a Savage No4 Enfield and MKVII ammo, we concluded the tests on the right rear door. These rounds also just made a dent and bounced back at us. We concluded it was probably the angle of the rear doors causing the rounds to bounce back at us.

The tests continued with poking holes through the front of the PK and seeing if we could crack the engine block. We did quite a bit of damage with the 7.62X51 AP and SS109.

I have a hard time believing any other tests I hear since I've been there and done that on Uncle Sam's tab.
Original URL (now dead): http://www.gunboards.com/forums/topic.asp?TOPIC_ID=8056&whichpage=2

Note that the 5.56x45 NATO, in spite of its known inferiority at penetrating many common building materials and media such as auto windshield glass, does better against some kinds of armor than many more powerful rounds.

If you own any 5.56 NATO (meaning it has the SS109 steel penetrator in the bullet), I suggest saving it for a rainy day rather than shooting it. Practice with something else.

Solid brass spitzer bullets, either turned on a lathe or bought commercially, also have excellent penetration.

Yeah the 5.56x45mm NATO was designed specifically for punching through body armor, which sucks ass since those asshole insugents don't use body armor in Iraq. The bullets fly right through them, causing damage, but not enough to stop them in their tracks. Especially when those bastards are on drugs. One of my buddies did land a well placed 5.56 round on the hood of a vehicle from a littlebird helicopter, which penetrated the engine block and bounced around for a bit, completely stopping the car. Alot of what a bullet can do depends on the type of ammunition.

We were trained to do the "controlled pair" to the chest and then 1 shot to the head, just to make sure. Firing the 7.62x51mm never posed an issue when it came to unarmored personnel. It was big enough to stop people, even if it was FMJ. If it were up to me and the country had the money for it, I would upgrade all of the M-4s to chamber 7.62x51mm.

Although my experience with firearms is rather limited, I have to agree with your sentiments on 7.62 rounds. In all reality, the 5.56 round has very little to offer in modern combat. Yes, it has a higher velocity and yes, you can carry more of it, but it is often many times less efficient. In urban combat, 5.56 rounds make even less sense, since most firefights are rather short-lived (minimal ammunition requirement) and the velocity of the round has very little bearing on its capability in close quarters.

On a related note, have any of you seen that (relatively) new episode of Futureweapons with the M4 chambered to fire .50cal rounds? It is being tested as a compliment to the M4, almost like the M203 minus the boom and the fact that it can be fired alongside the M4. Its main selling point is its ability to drop anything alive (its effectiveness has not yet been proven for zombies, though I would imagine that it would be on par with the shotgun or the ever popular chain saw) or anything with wheels with a single shot.

Back on topic. If it were me and there was a vehicle driving at me, I would want the most obnoxiously large and otherwise excessive weapon I could find. An MG-42 would be nice, if anyone still used them. In lieu of an MG-42, the bigger and faster, the better.

Just to clarify, it should be mentioned that the M4s chambered for .50 is not a .50 BMG, its a .50 Beowulf. Firing a .50 BMG from an M4 platform would be suicidal. Here is a picture (http://www.gunblast.com/images/50Beowulf/Mvc-005f.jpg)with a .50 Beowulf compared to a 5.56x45mm round. I'm assuming gaussincarnate knew that, I was just clarifying. You make an excellent point in that the 5.56 is not very useful in CQ combat. You need something that knocks the target down, not a round that flys right through with minimal damage. The .50 Beowulf is a perfect round for knocking the bad guy on his ass, as is the 7.62x51mm or Soviet 7.62x39mm.

MG-42s were awesome... in the 40's. Today I would prefer a Mk-48 (http://images.military.com/pics/SoldierTech_Mk48-1.jpg), which is what I carried on my tours in Iraq. Reliable, relatively light at 18.26 pounds, easily fired from the standing position, and fired the 7.62x51mm(.308) round. My personal favorite weapon of all time.

I've never tried the MG42 but I have quite a bit of experience with its successor, the MG3. (which is virtually the same thing, except for being chambered for the 7.62X51mm instead of the WW2 7.92X57mm). Probably having fired a couple of hundred thousand rounds with it. With a weight of 11.6 kg, it's not my first choice of personal weapon. The rate of fire is awsome (1500 rpm), which makes it a little bit hard to control for some if you fire it from a standing position (easily remedied by leaning forward). The mechanism is also relatively complex and can't take as much abuse and neglicence as its Russian counterparts.

But mounted on a tripod or fired from a prone position, I wouldn't trade it for any other machinegun. The sound, the air-pressure, the power it projects is just awsome.

Perhaps it's time to straighten out a few things. First of all, the original AR-15/M16s were equipped with a 1/14 rifling twist, since it was well known that small, high velocity, understabilized varmint bullets could inflict incredible tissue damage, since it exhausted all of its KE in the target in a very abrupt manner. It was soon learned that 1/14 was a little too loose, with bullets deflecting off of twigs, heavy grass and other small vegetation. So it was tightened up to 1/12, and went to trials in Southeast Asia.

I got to see some films of the trials, and they took some stomach to watch. In one instance, a guy in black pajamas with an SKS is running along, when suddenly most of his head explodes in a cloud of pink vapor. In another a similar scene, only he takes the hit about halfwat between the right nipple and shoulder, and his arm goes flying. But the one that got to me was the guy who took the hit in the lower left abdomen. The hydrostatic shock was so severe that his intestines were extruded through his right rib cage. All of this with 55gr. square heel bullets.

As usual, leave it to the Army to fuck up a good thing. They go to a 62 grain boattail, in the interest of more penetration, but now the bullet's too long to stabilize with a 1/12 twist. So they go clear down to 1/7, and now the slug remained stable in flight . Unfortunately, it also remained stable through doors, clothing, flesh, bone, more flesh, more clothing, and whatever else was farther downrange. So the Army now issues noisy, long range icepicks. This is the exact opposite of the whole original concept! Instead of a weapon that will gouge big, ugly chunks out of an opponent, guaranteeing he's flattened, they've got one that punches little, dinky holes in the bad guy, guaranteeing that he's good 'n pissed off!

As for other cartridges in the AR-15/M-16/M-4, they're all limited by the size of the magazine well. The 6.5 Grendel, 6.8 SPC, .450 Bushmaster and .50 Beowulf all fit within these confines, although the bigger ones must be single stacked, limiting capacity.

There are a couple of exceptions here. MGI (formerly MWG, think "90 Rounder") offers a modular lower receiver with an interchangeable mag well, to switch between 5.56 and 7.62x39. Needless to say, you'll need a 7.62x39 upper to go along with it (or any other nonstandard caliber, for that matter). The materials and workmanship are first class, and it's reflected in the price (about $450 for just the bare lower).

Another one is a .50 BMG upper that fits on a standard -15 lower. It's made up in Oregon, but the name of the company escapes me. As you might expect, it's a single shot affair. But rumor has it that it's rough on lowers. I'll have to look into it further.

Generally, the larger caliber rounds (except the .50 BMG) are good for penetrating brush, but not so much for armor. The smaller, higher velocity projectiles can be deflected more easily, but will work better on light armor. This, of course, is contingent on bullet design and construction; a tungsten core will work way better than lead.

I've probably omitted a few things. I'm sure someone will let me know.

A few things. 5.56mm NATO is not just SS109. It includes 193, 196, etc. There are many makers of .50cal uppers for the Ar 15 lower receiver. There is the .50 Beowulf, the .50 AE and the .50BMG. Within the .50BMG there are many manufacturers. I own an Ultramag 50 that is a bolt action magazine fed upper. Bohica Arms, the Ferret50, are examples of other companies that make them. Also don't forget about the .458Socom, 3oo Fireball and all the WSSM uppers that are made. There are some excellent bullets that will easily penetrate armor. The only problem is that they will/can't be sold to civilians. RBCD ammo is a perfect example.

I've probably omitted a few things. I'm sure someone will let me know.
Yup, but that was a pretty good summary.

The trend towards the ultra-light, low-impulse vHV rounds isn't going to stop any time soon. The 5.56 was really a compromise in itself, since the British researched had already come out with the 4.7 (iirc) round that was put into the first versions of what eventually became the L98 and SA-80 rifles. (The first ones were in the 60's, and have wooden stocks rather than plastic.)

The USA decided on 5.56 and through whatever means got it adopted. Now, 40 odd years later, everyone's till looking at the smaller rounds.

As a side note, the quote about the penetration of the armoured car above is nothing new. Basically, if you hit the material faster than a certain critical speed, it will (not have time to bend and so) shatter. Below that it will (have time to) bend. The actual size of the bullet has nothing to do with it, all else being equal. It's just a hell of a lot harder to fire a bigger bullet as fast as a little bullet.

Well, the .223 Rem. (I'm using the civilian terminology to distinguish it from other, similar cartridges) was developed because the the round that was originally worked with for the AR-15 was the .222 Rem, and wouldn't quite satisfy one requirement the Army had. They insisted that the round absolutely HAD to reliably penetrate a steel helmet at 300 yards. Never mind that you don't see your average ground pounder taking head shots at that range, especially through open sights.

So the ArmaLite crew got together with Remington and figured that they could increase the powder capacity by up to 12% without unduly increasing the port pressure. (Dont forget that they were originally working with IMR powder.) That became the .223 Remington. NATO acceptance didn't occur until many years later, then picking up the 5.56x45 designation. (By the way, all the well known "22" varmint rounds have an actual bullet diameter of .224.)

Oh, and here's the skinny on the ammo that got all those soldiers killed. As stated above, the rifle was originally developed for IMR (stick) powder. As long as that was used, port pressure (the pressure inside the bore directly behind the bullet when it passed the gas port) was not a problem. But after WWII, the military had huge surpluses of just about everything, including propellants. Everyone was geared up for another couple of years of war, for the invasion of the Japanese home islands. Then BOOM! Hiroshima, Nagasaki, the war ends abruptly, and we're sitting on these enormous stockpiles off STUFF.

One of the things they had lots of was tons and tons of howitzer powder, and some bright boy in Army Ordnance decided it could be reclaimed, and remanufactured into small arms propellant. This turned out to be a bad idea on a couple of fronts. The small arms propellant lines were geared up for ball powder. The Army decided that this was desireable, since spherical powder would provide higher pressures & hence higher velocities.

It also meant that the higher working pressure would translate into higher port pressure and, by extension, more violent operation of the mechanism. It occasionally became so severe that the little elastomer bumper on the recoil buffer would be beaten to fragments, allowing metal to slam onto metal. This could eventually result in a peening action between the bolt & carrier, actually swelling the carrier diameter slightly, and also slightly misaligning the gas key, so it would tend to bind in the protruding gas tube at the front of the upper receiver.

But this isn't the half of it. That howitzer stuff these huge batches of ball powder were reclaimed from was chock full of Carbon. Not only that, the 10-12 Ksi extra working pressure meant that the bullet swelled against the bore surface so hard that the edges of the gas port would shave minute particles of the Cupro-Nickel gilding metal off of the jacket. This formed an alloy with the excess Carbon which was just harder than Chinese arithmetic. This amalgam would blow through the gas tube in a high enthalpy jet that would very efficiently deposite it all over the gas key, bolt carrier ports, gas rings, bolt stem, extractor, ejector, firing pin etc. The alloy was much harder than Carbon alone, and would just lock everything up solid. And even if that didn't do it, it wouldn't take much other contamination to finish the job.

Of course, the Army immediately pointed it's finger at Stoner, but he wasn't having any of that shit. He actually appeared before several congressional commitees, and ran it down in such a manner that there was no way for the Army to squirm out of it. He told them he never claimed the weapon would never need cleaning, only that it would be resistant to fouling, but that that claim was based on the use of the much cleaner, lower pressure IMR powder. When the Army decided to deviate from the original specs, that was when the trouble started.

By that time, though, there were millions of rounds of the dirty stuff in-country, and it would be a logistical nightmare to attempt to completely replace it anytime soon. So cleaning kits were issued (which should have happened in the first place), and armorers were provided with chrome-bore replacement barrels, as were later deliveries of new rifles. (And then there's that goddamned silly forward assist button, which the original designers hated, not to mention that 3 round burst. But that's for another time.)

Anyway, that's how Stoner ran it down to me.