M4 / M16A2 technical question?

Question

What are the differences (lenght and twist rate) between the barrels of the M16A2 and the M4?

what about the velocity loss (m/s or fps) when firing 5,56 nato standard bullets with the shorter M4?

Is it known what brand of powder does the M855 ctg use?

...and what about the "rumors" i heard about the lack of stopping power of the 5,56 nato ctg? are there some serious complainings about it?

Answer 1

Every thing you want to know is right here:

http://www.ammo-oracle.com/

Answer 2

I build match AR rifle.   Email me.

I have chronographed my 20" match barrel with several 16"  M4 style in 1:9 and 1:7 twist.  The 20" barrels are usually right on the money for specified velocities.  In my 16" carbine barrels they are nearly 390 fps lower.  I would expect the velocity in a milspec 14.5" to be an additional 150 fps lower.

The 14.5" M4 barrel was introduced for urban warfare against human beings - not animals, not hunting.  That missing 1.5" from the M16A2 makes a big difference when going up a staircase and entering a door way!!

You can improve the stoppage power of a 14.5" or 16" barrel by using more effecient bullets - like the Barnes 70gr Triple Shock or Hornady A-Max or Nosler Ballistic Tip - but these are not available to the majority of our troops under the rules of warfare (Geneiva Conventions).  (Combat snipers use non GC ammo).

The M4 is shortened for urban warefare.  It is what it is. When you take a 90 passenger school bus and shorten it to 30 - the passengers all arrive just fine - and does the job.  It just is no longer a 90 passenger bus.  The 20" barrel is standard and developes the full 5.56mm velocities - but - is too big for the urban situation.  You have to play give and take.  

Hope this helps  

Answer 3

Twist rate should be the same, but barrel length is 20" for the M16A2 and 14.5" for the M4.

Yes there is a velocity loss with the shorter barrel. It results in the same weight / grain bullet leaving the muzzle at a slower speed. This reduces the length from the barrel to the target that the bullet will reliably fragment because it will slow below the "reliable fragmentation" speed of 2700fps ata acloser distance. A faster bullet will have a higher starting velocity and will take longer to slow below that speed, resulting in a longer range with which it can reliably fragment.

The "lack of stopping power" comes from the misconception that when you shoot people in the chest they always fall down. It also comes from a  misunderstanding of the proper use of the M4. The shorter barrel reduces fragmentation and so permanent wound cavity is the result of crushed tissue that is directly in the path of the single projectile that may swap ends in the body. With extremely thin adversaries it may pass through leaving the 5.56 diameter hole with no tumble. When the round does fragment, the bullet seperates into multiple pieces, each taking a seperate path and increasing total tissue distruction with a higher likelyhood of perforating something vital such as major arteries, spinal column, heart and so on.

The M4 was designed for close range engagemnets in tight confined spaces. It does that job well.

The 5.56 has plenty of so called " stopping power". But it can not, nor can any other round, make up for poor placement.

EDIT:  GettGo I think you have the twist rate to projectile length/weight backwards. It's the 1/7 that is better for heavier bullets, the 1/9 that is ideal for 55gn bullets and the old 1/10 or 1/12 for the light 40gn bulets used in the .233 loading.

Metro: Unfortunately it isn't the speed alone, its the permanent tissue damage. The speed causes the bullet to violently fragment and send particles in different directions making a highly effective round. If it doesn't fragment the resulting wound is just a hole with a fmj or it will tumble trying to go base forward the (heavy end) and make a slightly larger hole. The best way to learn this stuff is to research forensics articles that describe GSW (Gun shot wounds).

Answer 4

As far as the M16A2 goes," the ideal twist rate for the SS109 projectile is 9 in (229 mm), a 7 in (180 mm) twist rate was chosen to stabilize the much longer L110 tracer". It’s really all that you make of it . . . you just need to pick the right grain of bullet for the barrel you have. As far as velocity goes . . . that is a double edged sword in itself. I'm glad you lumped so many of your concerns into this question. What you need to realize first of all is that if you don't like the twist rate or length of your barrel another can easily be purchased, and then you can put yours up for sale to recoup your money. Next you need to understand that the faster the rate of twist, the less weight a bullet needs to be stabilized. For instance, the rifling in the M16A2 has one twist in every seven inches of barrel; so this 1:7 rate of twist is great for stabilizing 55gr bullets. That in itself is a blessing in disguise, because the 55 grain ammo is cheaper than the 62grain ammo by almost $100.00 a case (1000.) The 1:9 twist is better for the 62 grain bullets, and the older mini 14s used a 1:10 twist was maximized by 77 grain bullets, the newer ones are 1;9, and until the late 70's/early 80's they used a 1:7 twist too. The last thing I need to point out to you is that lighter grain bullets achieve higher velocities, however higher velocities are accompanied by lower terminal energy. That is where your double edged sword lies. Heavier bullets provide more stopping power, but are slower than lighter bullets. The sectional density and ballistic coefficient also are a factor in this, but I am not even going to go into that. I will include a few links to chuck hawks if you want to research the concepts on your own though. Also, I included a link to PK Firearms which will allow you to see the multitude of barrels at your disposal. It's not rocket surgery to guess that the shorter the barrel the less velocity you'll get out of it, so I’ll leave that alone. Lastly, I'm sure you are not aware of this, or you would not have asked about the stopping power of the 5.56 NATO round; the fact is that FMJ bullets suck! The Geneva Convention has a mandate that any killing done on the battlefield will be done in a humane way, which means no lead bullets, for fear that a soldier might get lead poisoning, and also because lead nosed bullets mushroom on impact. Obviously hollow points are out of the question on the battlefield too. If you have any questions about stopping power from the 5.56x45 NATO round, just buy you some 69 grain Lapua hollow points, and you need worry no longer. Be sure and check out the link to the ballistic chart from guns and ammo magazine I sent and you'll see the correlation.

Answer 5

in order to answer your question let's go back a ways. When first offered by Eugene Stoner what we now know as the M16 was actually chambered in .308 win (7.62 nato). But  due to mostly political influence it was changed to 5.56 nato (very similar to the .223 Win) the original M16 had a 1 in 14" twist with the 55 grain FMJ (ball) ammo and moved in excess of 3400FPS. this light and very unstable bullet would tumble on impact causing horrendous wounds. The next generation featured a twist rate of 1 in 12" which still left the bullet unstable again causing massive wounds. Next came the 1 in 10" twist rate ( in my opinion the very best) which stabilized the 55 grain bullet a little better, giving better down range accuracy, but would still begin to tumble an inch or two into the enemy's body causing significant wounds capable of ending the fight then and there. BUT, the military being what it is, and wanting to "improve" the down range accuracy and penetration against a (then) steel helmet, decided not to do the right thing and go to the .308, instead they  went to a heavier  5.56 bullet. This did give better penetration but showed little increase in accuracy, and in fact started to show less wounding capabilities, but still not bad. Then, they went to the present 1 in 9" twist on the M16 (note I am not discussinng the different models as that is not relevent to your question and I could write a book trying to cover everything) and then decided to go with the smaller shorter M4 version that we see today. So, between the heavier bullet, the much faster twist rate of 1 in 9" (they are discussing a 1 in 8 twist!)  and the loss of velocity from the shorter barrel,it stabilized the bullet much more, which means it tends to punch thru the enemy without tumbling or transferring energy which leads us to the truth that our soldiers are hitting the bad guys multiple times to try to put them down. This allows the bad guys time to continue doing evil things to our soldiers before the bad guys go down.

I really like the AR platform, and have built many different styles of rifles and carbines on it. I enjoy the 1 in 10" twist IF you can find it, and settle for the 1 in 9 if I have too, but I still use the lighter 55 grain bullet, however, I am not limited to the Ball ammo, and use a quality HP round for anti personnel which works remarkably similar to the early rifles with the 1 in 12 twist as far as wound characteristics. I think  the best choice is to drop out of the extinct accord we signed years ago,and go to the hollow point ammo if we are going to stay with the .223. This would solve the problems and put the bad guys down right now!! ( and save you and I billions in taxes)

But, in my humble opinion, Eugene Stoner was, and still is correct. The same rifle in .308 win (7.62 nato) would have the best performance at any practicle range against personnel, at decent range against light vehicles, and with specialty ammo like AP, tracer, incendiary etc it would fulfill a meriad of needed funtions. It would have greatly extended range, much better accuracy at longer ranges, much better penetration and even with ball ammo, puts mr bad guy down fast!!! The argument is that a soldier with a rifle in .223 can carry more ammo than one with a .308 caliber weapon. But just like with a 9mm vs a .45acp, if you have to fire more rounds to put each bad guy down using the .223, what sense does it make when one round of .308 would do the job better?  But instead of doing things right and going to a .308 (7.62) caliber version, or using the existing lowers of an AR and switching to a much better upper firing a better caliber, they are going to spend billions developing an all new, similar rifle in a whole new caliber which will cost billions more to get the parts, ammo etc into the inventory. Billions that you and I have to pay.

Hope this helped answer your question.

shoot safe

Answer 6

5.56, 5.45x39, and 7.62x39 are cartridges actually designed to wound rather than kill because caring for a wounded man in a warzone ties up far more resources than a dead man.