So, a thread on the adoption of 5.56x45 mm as the NATO caliber and why is the 7.62x51 making a comeback. At the outset, let me give credit to Anthony G Williams editor of Jane's Small arms Amn and others who I will quote as and when reqd 1/n

Brief history, not too far back just to the end of WWI. At the end of the great war, both the US and UK came to the conclusion that the .30- 06 and the .303 that they were using, were overpowered, heavy, long and generated too much recoil to be really effective 2/n

The Brits got down to researching what caliber would be optimal for small arms in 1934 after analyzing feedback recd from tps. However, before they could publish their report, WWII started and the report did not see the light of the day. So, both fought with same cal wpns 3/n

In the meantime, other countries like Japan was with the Arsika in 7mm the Italians had another wpn in 7mm, and ofcourse the Getmans devp the first ever aslt rif the StG 44 in 7.92mm. Post the war ofcourse the AK was born. These are important milestones in devp of small arms. 4/n

However, going back to the US and the Brits. By early 1950, the Brits were at their research again while in the US, they were quite happy with their Springfield. 30-06 and the M1 in service. It was post the Korean war that they started to rethink the caliber and wpn 5/n

The Brits meanwhile, completed their study and the final result that came was based on wt, length, recoil and terminal ballistics(which they studied by firing into animal carcasses) the optimal caliber was in between 6.25 to 7mm. Anyway, the US being what it is, Armalite 6/n

Beat everyone and prepared the AR 10 and got the nod for induction as the M14 chambered in 7.62x51. Now how much difference between the .30-06 and the 7.62x51? Well some saving in wt, some in recoil but not such a big deal. But the big deal was for the manufacturers 7/n

So, anyway, the US unilaterally made the 7.62x51 as the std NATO caliber sometime in 1957. The others also followed suit with FN and the CTEME and many more. However, the 7.62x51mm had a distinct disadvantage of not being able to fire controllable bursts. So, again the US arms8/n

Industry came to it's own rescue and commissioned a study that more round on target will lead to better effect. Pl note till now the US way of thinking has not even considered terminal ballistics whereas the Brits had almost 3 decades ago. In comes Armalite again with AR 15 9/n

Which it sold to Colt (patents). Pl note the the alacrity ok, 1957 - 7.62x 51mm adopted and AR 15 design sold to Colt in 1959. Do only I see a pattern here? Anyway that is the birth of the 5.56x45mm wpn and amn. Fun fact, just convert 5.56 into inches and see. 10/n

Yes, it nicely converts to .22. The same .223 that is classified be the US game hunting association as being suitable for vermin and small game ~ 40 lbs. Interesting? Yes. So the amn used to kill small game was now to bee used against humans ofcourse after militarizing it 11/n

Anyway, cut to Vietnam. The M14 was found to be unwieldy in the jungles and hey presto, the answer was ready back home as the M16. So, the M16 was inducted post haste. By 1969, it was seeing action in Vietnam. Grnd feedback of the M16 was very poor. Same stoppages, etc 12/n

And the ability of the en to continue fighting after being hit multiple times. Sounds familiar? Yes it is. So, all the stoppages double feed etc were attributed to improper cleaning again familiar to those who have read my thread on the devp of INSAS. Anyway, the feedback wa 13/n

Taken into account by Colt. And Colt started to work on it. Resultantly, the M16 and later the M4 was fitted with a forward assist. Anyway, the US continues to use the M4 despite feedback from Vietnam,Somalia and even Afghanistan. Do ask google baba about a research paper 14/n

Taking back the Infantry by 500 yds. Even the Somalia episode was disregarded as improper placement of shots. Even we faced the same issues about 30 yrs later. Now a jawan or a US grunt, has been trained to hit the center of mass. Do u suddenly ask him to start 15/n

Aiming somewhere else? But anyway, digressing. So, next up, the whole world and their uncles wanted the 5.56x45. Then came a US navy Doc, Lt Col Martin L Fackler, who actually started the studies for the US as far as terminal ballistics is concerned. 16/n

But by then it was too late
The US was heavily invested in the M4 till they got a wake up call in Afghanistan. That is the time when they brought back the M14 as a EBR/ DMR and the M240 as an add on SAW. So, basically a 8 man squad had the following wpns and amn 17/n

M4s, M14 in 7.62x51 as DMR, M249 SAW(belted 5.56x45) and M240(7.62x51) belted. Lgs? Nightmare! Even the Brits had similar issues. This took off from some interview with a soldier who said(and that's seared in my mind) that the Taliban dont even consider our suppressive 18/n

Fire as anything. They continue to engage us as if our SAWs dont exist. We are engaged at longer ranges, our capability to react is limited unless we call for Arty or Air. This I'd read sometime in 2009/10. And the feedback was from 2004/05. 19/n

So, in our context when we read about the failure of the INSAS, it's not just the wpn, it's also the caliber. Anyway both the M4 and the SA80 have become successful as far as reliability is concerned. Thesevwpns fire when told and are fairly accurate. However, effect on tgt? 20/n

Well I get back to the same issue of effective against a 40 lb vermin. Approx 18 lbs animal. So, after the British research of the 30s and 50s, some companies came up with the 6.5x39 Grendel and the 6.8 mm SPC as an intermediate cartridge. However, despite their performance 21/n

Which incidentally is still better than the 7.62x51 out to 1000m/800m resp, these 2 are still curtailed since they have tried to be a part of the AR15 platform. Their true performance can only be unleashed when the developers come out of the design limitations of the AR15 22/n

Anyway, a lot of time has passed from the time Lt Col Martin Fackler did his research and introduced the gelatin block for the study of terminal ballistics but the whole world is stuck with the 5.56x45. Some notable exceptions being the 5.45 and 5.8. However, the choice 23/n

Of these calibers being selected and their terminal effects are still shrouded in mystery. But, let's go back to the 1950s in UK. Remember they'd said the optimal caliber is between 6.25 and 7mm? Despite the 6.5 and the 6.8 proving themselves as being in the ideal rg, 24/n

Including reduced recoil, flatter trajectory, more retention of energy over longer ranges, terminal ballistics even with the self imposed restrictions of having to be compatible with the AR15 platform with minimal possible changes, they have not yet been adopted by anyone 25/n

In the world as a std caliber for their military rifs. Ok, so what is the wound/terminal ballistics I've been referring to so far. To put it simply, it is the interaction of the bullet with the target upon striking. Again, going back to Lt Col Martin L Facklers' research, 26/n

He had shown how different calibers behave differently in a gelatin block(which closely approximates the human soft tissue). As per his research, there are two effects which take place when a bullet strikes a human body. First is the hydrostatic shock leading to 27/n

A temporary cavity, and second is the permanent cavity caused by the path of the bullet itself. Now, the temporary cavity by itself can cause damage to vital organs due to the shock effect, however, the surrounding tissues get back to their original shape due to elastic 28/n

Nature of tissues, however, the permanent cavity does not get back. Hence, the more the bullet travels in the body, the more the bullet is effective. I had a chart on his observations somewhere but unfortunately have misplaced it and google baba is not being too helpful 29/n

Anyway, the long and short of it is, the 7.62x51 NATO rd tumbles within the body while, the 5.56x45 SS 109 disintegrates under ideal conditions. The 7.62x51 and even the 7.62x39 have fairly stable tumbling properties upto around 300yds but the 5.56x45 was inconsistent 30/n

In its fragmentation. At around 100 yds the bullet neither fragmented nor tumbled within approx 25 cms of thickness of the target and started to fragment only laterbetween 150 to 250 yds the bullet showed fairly decent fragmentation. Beyond 250 yds it didnt have adequate 31/n

Energy to fragment, some tumbling effect was seen. Hence the caliber is considered less lethal. This and the ground feedback led to the biggest con of the 20th century that ' the 5.56 amn has been designed to injure and not kill becoz, evac of an injured en takes 4 others' 32/n

However, the perpetrators of this con hadn't really fought wars when even if ur buddy is injured, u only get to evac him only after the mission is complete. However the con worked and today, approx 80% + of the world is equipped with 5.56 wpns. The only notable exceptions 33/n

Being Russia with their 5.45 and China with their 5.8. But even these calibers are not within the optimal zone of 6.25 to 7mm as recommended by the Brits sometime in the 1950s. Even we selected the 5.56x45 for the INSAS and look where we landed up 34/n

During the Afghan war, a large scale survey was carried out by the US army sometime in 2004/05 and one particular point made by a soldier has stuck to my mind, 'they just ignore the suppressive fire of the SAW'. So, carrying more amn to the battle may not have been the best 35/n

Option if the en just ignores it and keeps engaging u. Hence the M240 and the M14 EBR. A fact acknowledged even by our planners when they decided to equip all RR with only the AKs and not INSAS. 36/n

However going by the current procurements and proposals, it seems that the IA is also heading down the same path with 6 wpns in 7.62x51, two in 5.56x41, one 7.62x51 belted one 84mm RL and one 9mm pistol in a section. I'm not even clear where does the AK 203 fits in 37/n

A logistical nightmare. Not just that, the whole concept of reorg will need to be rethought. Still not too late. My suggestion; let the AK 203 be dply at 8 per section, and the LMG also to be in the same caliber with both belted and magazine options. 38/n

Will save us a lot of sweat in peace and blood in war