# 5.56mm velocity and pressure vs barrel length study.



## Diamondback 2/2 (Mar 16, 2016)

Barrel Length Studies in 5.56mm NATO Weapons


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## AKkeith (Mar 16, 2016)

That study seemed fairly indepth, especially with the chamber pressures at exit and the impact of a suppressor. To me it did seem like they lacked some definitive evidence of proof on some statements. This statement stood out to me when they provided no further evidence, "M855 bullets traveling below 2,500 fps when impacting a target will not produce a lethal wound channel."


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## Gunz (Mar 16, 2016)

AKkeith said:


> ...This statement stood out to me when they provided no further evidence, "M855 bullets traveling below 2,500 fps when impacting a target will not produce a lethal wound channel..."



That's a pretty general assumption on their part. It depends on where it hits you.

Great find, BTW, @Diamondback 2/2


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## Diamondback 2/2 (Mar 16, 2016)

Yeah I agree, you put a M855 in the right spot, 2500fps or not, its lethal.


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## Totentanz (Mar 16, 2016)

AKkeith said:


> That study seemed fairly indepth, especially with the chamber pressures at exit and the impact of a suppressor. To me it did seem like they lacked some definitive evidence of proof on some statements. This statement stood out to me when they provided no further evidence, "M855 bullets traveling below 2,500 fps when impacting a target will not produce a lethal wound channel."





Diamondback 2/2 said:


> Yeah I agree, you put a M855 in the right spot, 2500fps or not, its lethal.



Or what exactly drives the conclusion that 2500 fps is the magic cutoff.  That statement caught my eye as well - Is it a specific probability of a hit being lethal below that speed?  Or is there some ballistic effect that occurs below that point?  I agree with @AKkeith that without further explaining it, just positing it as fact is a bit dubious.


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## Diamondback 2/2 (Mar 16, 2016)

I imagine it has to do with the internal wound cavity with regards to the high velocity tissue expansion. But that's just a guess, as I'm not aware of any ballistic gel tests that are specific to M855 and 2500 fps velocity at impact of the gel.

We all know that 5.56 works by high velocity coupled with tumbling and fragmentation of the bullet. But at what speeds are required for those effects to take place, I'm unsure of. That said, a 36gr .22cal moving at 1,000 fps has killed many of people. So it's doubtful, to me anyway, that a 62gr .22cal bullet moving at 2.5 times that speed will not produce a lethal wound when fired at a vital organs or the brain housing group.

$.02


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## Florida173 (Mar 16, 2016)

Aren't we all using m855a1 now?


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## Diamondback 2/2 (Mar 16, 2016)

Florida173 said:


> Aren't we all using m855a1 now?



USMC is still using M855, but yes Army is M855A1 currently. The M855A1 is supposed to be a hotter round making up for the shorter barrel in the M4, but that's all after my time so I don't know much about it.


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## AKkeith (Mar 16, 2016)

Florida173 said:


> Aren't we all using m855a1 now?


Come on @Florida173. Not all of us are high speed. The Marine Corps is just getting the M4. We are still all excited about how cool they are. Slow your roll.


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## Brill (Mar 16, 2016)

Florida173 said:


> Aren't we all using m855a1 now?



300 AAC baby!!!!


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## busdriver (Mar 16, 2016)

He says the shorter barrel has a higher muzzle pressure (not a surprise by the way, muzzle brakes work better on shorter barrels for a reason) but the same 7 inches of "dwell" is appropriate for a 14.5 and 20 inch barrel?  Not to mention if you just take the literal meaning of the word dwell, port distance from the chamber would be dwell and distance from the muzzle more of a port open time.  Then there's the mass of the BCG/buffer and the actual port size.  
Nope ole Eugene was perfection, can't change anything; it's like changing the 1911, except when Browning changed it, that was ok.


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## Etype (Mar 17, 2016)

AKkeith said:


> That study seemed fairly indepth, especially with the chamber pressures at exit and the impact of a suppressor. To me it did seem like they lacked some definitive evidence of proof on some statements. This statement stood out to me when they provided no further evidence, "M855 bullets traveling below 2,500 fps when impacting a target will not produce a lethal wound channel."





Diamondback 2/2 said:


> Yeah I agree, you put a M855 in the right spot, 2500fps or not, its lethal.


It's been proven more than a couple times over that a .22 LR is a lethal round, even while moving quite a bit slower than that.

Getting a hole poked in you, regardless of speed or size, is never a good thing- the academics need to quit trying to tell us otherwise.


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## DA SWO (Mar 17, 2016)

Etype said:


> It's been proven more than a couple times over that a .22 LR is a lethal round, even while moving quite a bit slower than that.
> 
> Getting a hole poked in you, regardless of speed or size, is never a good thing- the academics need to quit trying to tell us otherwise.


I seem to recall pics of the IDF using Ruger 10/22's as a terrorist elimination tool.


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## Diamondback 2/2 (Mar 17, 2016)

DA SWO said:


> I seem to recall pics of the IDF using Ruger 10/22's as a terrorist elimination tool.



They actually use it for crowd control, using sub-loads to the leg of a protester. Not lethal, but gives you an accurate stand off distance. About the equivalent of a high powered pellet rifle.


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## Brill (Mar 17, 2016)

Etype said:


> Getting a hole poked in you, regardless of speed or size, is never a good thing- the academics need to quit trying to tell us otherwise.



Pashtun boys have said this for decades now.


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## AWP (Mar 17, 2016)

lindy said:


> Pashtun boys have said this for decades now.



I hate myself for Liking the accuracy of this statement.


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## Brill (Mar 17, 2016)

Freefalling said:


> I hate myself for Liking the accuracy of this statement.



@Etype is a sniper so he never misses!


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## DA SWO (Mar 17, 2016)

lindy said:


> @Etype is a sniper so he never misses!


Would the womenz in his life agree or disagree?????


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## gafkiwi (Mar 17, 2016)

Apparently at our recent rifle trials (NZDF) they found some of the 14.5's more accurate than some 20 inch platforms out to 600m. Navy and Airforce are going with LMT MARS-L's with 14.5 inch, Army is going with 16 inch and it is apparently to do with the difference in terminal ballistics at 600m of the two. NZ Army Manoeuvre/Combat trade weapons qual with ACOG goes back to 600m.


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## Diamondback 2/2 (Mar 17, 2016)

gafkiwi said:


> Apparently at our recent rifle trials (NZDF) they found some of the 14.5's more accurate than some 20 inch platforms out to 600m. Navy and Airforce are going with LMT MARS-L's with 14.5 inch, Army is going with 16 inch and it is apparently to do with the difference in terminal ballistics at 600m of the two. NZ Army Manoeuvre/Combat trade weapons qual with ACOG goes back to 600m.



I think you have misheard/misunderstood  something, because its scientifically impossible. Shorter barrel equals lower velocity, lower velocity equal less consistency during external effects (wind humidity, etc, etc). If you use the same rounds in the same quality barrel, one being 5.5" shorter has done nothing but reduced the velocity on the round.

On top of that, if that was the case, Camp Perry National Matches, and primarily the President's hundred, would be shot with tricked out M4's vs NM AR15's (M16 without the selector) and M1A, etc.

But please do post the study if you have the link, I'd like to see what was done to come to such conclusions.


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## 8654Maine (Mar 17, 2016)

lindy said:


> Pashtun boys have said this for decades now.



That is awesome.


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## gafkiwi (Mar 17, 2016)

Diamondback 2/2 said:


> I think you have misheard/misunderstood  something, because its scientifically impossible. Shorter barrel equals lower velocity, lower velocity equal less consistency during external effects (wind humidity, etc, etc). If you use the same rounds in the same quality barrel, one being 5.5" shorter has done nothing but reduced the velocity on the round.
> 
> On top of that, if that was the case, Camp Perry National Matches, and primarily the President's hundred, would be shot with tricked out M4's vs NM AR15's (M16 without the selector) and M1A, etc.
> 
> But please do post the study if you have the link, I'd like to see what was done to come to such conclusions.



Sorry should have been clearer, that was across the range of rifles at the trial (4 AR based and 4 not, with both carbine 14-16 and rifle 18-20 options) and not comparative of the same platform with different barrel lengths, with some of 14.5's platforms out shooting other platforms in 18-20's.
What was the guys reckon was there wasn't a large difference in the groupings size's throughout between the carbine and rifle length barrels of the top performers i.e. not enough reason to go for a 18-20 vs 14.5-16 inch.


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## Diamondback 2/2 (Mar 17, 2016)

Well unless you run match everything, your shooting minute of bad guy at 600m, where the barrel length comes into play, again, is velocity. Being able to barley break the skin at 600m vs an actual penetration into the vitals is they key.

IMO the US Army fucked up going to the M4 exclusively. The M16 has its place, as does a 7.62x51 clambered rifle. The M16 is lethal at 600m the M4 from all the studies I have seen is not.


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## gafkiwi (Mar 17, 2016)

I believe that's the primary reason we are ditching SS109/F1 and going to 77gr across the board as our service rd to try for the best median between flexibility and effect.  That being said our Infantry sections already have 2 LSW/Mk 48's and a DMW/LMT MWS (20inch barrel) so at least a 3rd of the section are running 7.62


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## pardus (Mar 18, 2016)

gafkiwi said:


> I believe that's the primary reason we are ditching SS109/F1 and going to 77gr across the board as our service rd to try for the best median between flexibility and effect.  That being said our Infantry sections already have 2 LSW/Mk 48's and a DMW/LMT MWS (20inch barrel) so at least a 3rd of the section are running 7.62



So they are finally getting closer to a 1980's Section/Squad in fire power... lol

We should have never pulled the Jimpys from the section, and we should have adopted, and scoped, a 7.62 Bren, and added a 7.62 DMR  (putting a scope and a bi-pod on an SLR).


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## gafkiwi (Mar 18, 2016)

pardus said:


> So they are finally getting closer to a 1980's Section/Squad in fire power... lol
> 
> We should have never pulled the Jimpys from the section, and we should have adopted, and scoped, a 7.62 Bren, and added a 7.62 DMR  (putting a scope and a bi-pod on an SLR).


That mix would have been good for the time but with the 2 Guns, a DMW and a couple M-203's, I think its probably a better mix of mobility and firepower in the Infantry Bn's than the 80's.


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## pardus (Mar 18, 2016)

gafkiwi said:


> That mix would have been good for the time but with the 2 Guns, a DMW and a couple M-203's, I think its probably a better mix of mobility and firepower in the Infantry Bn's than the 80's.



Ah, two Jimpys, plus a scoped BREN and a scoped SLR, with also M203s is the same thing right? Well except the Riflemen have 7.62's as well...


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## Etype (Mar 18, 2016)

Expecting riflemen to engage targets at 600m is an exercise in diminishing returns.  You don't get a full exposure target in combat, you get head shots or a running target.

M240s kill at 600m, they also scare the hell out of the bad guys while the riflemen get closer to finish the job.

Laying on line at 600m and exchanging fire isn't how we win fights.


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## Florida173 (Mar 18, 2016)

Diamondback 2/2 said:


> Well unless you run match everything, your shooting minute of bad guy at 600m, where the barrel length comes into play, again, is velocity. Being able to barley break the skin at 600m vs an actual penetration into the vitals is they key.
> 
> IMO the US Army fucked up going to the M4 exclusively. The M16 has its place, as does a 7.62x51 clambered rifle. The M16 is lethal at 600m the M4 from all the studies I have seen is not.



I've never engaged anyone past maybe 200m...


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## CQB (Mar 18, 2016)

pardus said:


> Ah, two Jimpys, plus a scoped BREN and a scoped SLR, with also M203s is the same thing right? Well except the Riflemen have 7.62's as well...


I'm in your court in a broad sense, given that 7.62 will knock over most humans, 5.56, not so much. 

As an aside, isn't 7.62 now the new paradigm?


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## Diamondback 2/2 (Mar 18, 2016)

Florida173 said:


> I've never engaged anyone past maybe 200m...



I have, and from what I've read, it was pretty common in Afghanistan. 

Your point is?


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## Diamondback 2/2 (Mar 18, 2016)

Etype said:


> Expecting riflemen to engage targets at 600m is an exercise in diminishing returns.  You don't get a full exposure target in combat, you get head shots or a running target.
> 
> M240s kill at 600m, they also scare the hell out of the bad guys while the riflemen get closer to finish the job.
> 
> Laying on line at 600m and exchanging fire isn't how we win fights.



Hmmm, not one to disagree with you much, but I'm 50/50 on this one. Yeah if you have a 240B or heavier in your patrol to give support by fire as you maneuver, that would text book. That said, not every patrol is going to have immediate support by fire, hints the whole SDM concept and the EBR M14's. Having the capability to reach out and touch IMO is essential to an infantry squad or the like. That doesn't mean every soldier should be able to be consistent at 600m, albeit there wouldn't be the current "oh shit our soldiers cant shoot" in the Army Times, if they could shoot consistently at extended ranges. But lets be honest, most soldiers don't know how to properly group and zero, much less know how to call the wind, make a correction or apply a proper wind hold. I mean the Army is still using 25m zero's, when everyone knows the 50m zero is the better way to go with the M4/Aimpoint. I can go on and on, but the point being there is alot to be fixed, I think KD 100-300m qual with a fam-fire out to 500m is a good idea, and an SDM capability to 600m qual with a fam-fire to 800m is the best way to go. How they all get employed on the battlefield is a whole other discussion.


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## Florida173 (Mar 18, 2016)

Diamondback 2/2 said:


> I have, and from what I've read, it was pretty common in Afghanistan.
> 
> Your point is?



Pretty sure doesn't require additional explanation.  Good for you.


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## Diamondback 2/2 (Mar 18, 2016)

Florida173 said:


> Pretty sure doesn't require additional explanation.  Good for you.



So because you never shot someone past 200m the whole Army should stop there? Or let's make "good for you" remarks when I tell you I have shot at Iraqi's much further than 600m? WTF is that?

I'd actually like to know what your point of view is, or maybe clarify if that was a "hi I'm here post".


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## Florida173 (Mar 18, 2016)

Diamondback 2/2 said:


> So because you never shot someone past 200m the whole Army should stop there? Or let's make "good for you" remarks when I tell you I have shot at Iraqi's much further than 600m? WTF is that?
> 
> I'd actually like to know what your point of view is, or maybe clarify if that was a "hi I'm here post".



Maybe I took your "Your point is?" the wrong way.

Staying away from your rhetorical question... You sort of answer some of it in your next post. I'm more familiar with our patrols at least having an EBR or a SAW that can manage the 600m quite successfully.

I think your comment on KD 100-300m qual with a fam-fire out to 500m and a SDM out to 600m qual with a fam-fire to 800m is definitely a good idea, but fam fire on an m4 and acog should be out to 600m+. I've hit plenty of targets at 600m and 800m with the new m855a1 ammo and pretty consistent with 400-500m range. I'm not all that great of a shot nowadays though given the lack of range time we get.


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## Diamondback 2/2 (Mar 18, 2016)

Florida173 said:


> Maybe I took your "Your point is?" the wrong way.
> 
> Staying away from your rhetorical question... You sort of answer some of it in your next post. I'm more familiar with our patrols at least having an EBR or a SAW that can manage the 600m quite successfully.
> 
> I think your comment on KD 100-300m qual with a fam-fire out to 500m and a SDM out to 600m qual with a fam-fire to 800m is definitely a good idea, but fam fire on an m4 and acog should be out to 600m+. I've hit plenty of targets at 600m and 800m with the new m855a1 ammo and pretty consistent with 400-500m range. I'm not all that great of a shot nowadays though given the lack of range time we get.



Okay gotcha, I'm not at all familiar with the M855A1 or what its capabilities are. I know when I lived on the range, the M4/M855 combo was pretty well a crap shoot past 400m and past 500m we would occasionally have the rounds actually stuck into the corrugated plastic target backers. Hints my comments on the M16 or 7.62x51 weapon still having a place in an infantry squad. I like the M4 as much as anyone else as a general purpose rifle, but the EBR or even the M16, is still a good weapon to have in the squad.


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## AWP (Mar 18, 2016)

LOL....brilliant exchange.


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## gafkiwi (Mar 18, 2016)

Are the EBR's or 7.62 equivelant on standard issue in Infantry sections in the US (Army or USMC) or is it a unit/formation thing?


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## Diamondback 2/2 (Mar 18, 2016)

gafkiwi said:


> Are the EBR's or 7.62 equivelant on standard issue in Infantry sections in the US (Army or USMC) or is it a unit/formation thing?



Its an modified M14, to fill the squad designated marksman role.


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## gafkiwi (Mar 18, 2016)

Diamondback 2/2 said:


> Its an modified M14, to fill the squad designated marksman role.


Are they on standard issue to teams/sections? In the past I've encountered unit with and without.


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## Diamondback 2/2 (Mar 18, 2016)

gafkiwi said:


> Are they on standard issue to teams/sections? In the past I've encountered unit with and without.



I'm not sure, we had 4 M14's in our platoon, several units had M14's but not sure on how many per a team/squad/platoon. Some units have the SDMR (modified M16A4). I'm not sure how they decide it or how they acquire specific weapons like the SDMR or EBR.


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## Florida173 (Mar 18, 2016)

Like anything else.. Some units are the have's and some are the have's not


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## gafkiwi (Mar 18, 2016)

I suppose that one of the very few pro's to being a small military, its easier to outfit a couple Bn's vs trying to do the same with Div's


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## Diamondback 2/2 (Mar 19, 2016)

Honestly there are enough M14's in the inventory to outfit every squad with a couple. But the US Army leadership is stupid disconnected from the end result.


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## Etype (Mar 19, 2016)

Speaking on EBRs-
They suck, period. All the ones I saw were 3-4 MOA guns, aka couldn't reliably hit a head size target outside of 200m.

Head shots are what you need in the outside-of-CQB-range marksmanship game.  Bad guys don't offer full exposure/broadsize target presentation- the ones that do are already dead.

600m headshot on a 12" head is a 2 MOA target, now figure for winds, ranging error, and stress- I would want a 1 MOA .300 win mag at a minimum to feel confident in a first round hit.

Which brings me to another point- first round hits. You usually only get one try. If you get pretty close once, close enough to call a correction, the dude is generally going to move to find a different place to stick his head out of- especially in an urban environment.

As for the 7.62 argument- I wouldn't want to carry a gun that weighs twice as much and ammo that weighs 3x as much to only extend my super sonic range by 15%. That's bad math, even by common core standards.

ETA-


Diamondback 2/2 said:


> Honestly there are enough M14's in the inventory to outfit every squad with a couple. But the US Army leadership is stupid disconnected from the end result.


Honestly, I don't think the M14 is nor ever was a good weapon. Sure, Camp Perry and NMA M14s are great, but the ones they field as EBRs are junk.  I think the Army did a good job not sending them to Vietnam, and are making a sound choice today not reintegrating them.

You can't realistically do CQB with a scoped M14, a match quality M14 would rival an M2010 or SR-25 in cost, and the user still wouldn't have sufficient training.


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## Diamondback 2/2 (Mar 19, 2016)

Etype said:


> Speaking on EBRs-
> They suck, period. All the ones I saw were 3-4 MOA guns, aka couldn't reliably hit a head size target outside of 200m.
> 
> Head shots are what you need in the outside-of-CQB-range marksmanship game.  Bad guys don't offer full exposure/broadsize target presentation- the ones that do are already dead.
> ...



3-4moa with M80? My experience with the M14's, the EBR's, the SDMR, and the M110 were very different.

1) I carried a rack grade M14 in Iraq, shitty beat up wood stock, duct taped field expedient cheek piece, shitty Springfield optic mount, topped with a shitty MK4. With M80 ball yeah you had a pretty nasty group, use m118sb or lr, and that gun was 1-1.5 MOA all day. I had an issue with the mount, so I just zeroed Irons and kept rolling with it. As long as I did my part is was more than capable. Now that was 2003-2005, how beat up they are now (Joe and his fucking dental tools on the crown of the muzzle), I'll cede to your wisdom.

2) The EBR is a sub-moa gun, I've taken them out of the box, grouped and zeroed them, and taught 17 classes, specifically on that weapon. Now I personally fucking hate the stock they put on them, but its got a NM barrel and trigger. So I'm honestly confused with your responses.

7.62 argument) I agree with the weight comments, but its the NATO round. I'd much rather a 6.5Creed or the like.

M110 is a over priced POS, another one I unboxed and group and zeroed, 2.5moa all day. My cheap Armalite SASS with a Noveske barrel is sub-moa all day long. I can't believe the Army took it in the ass on the M110 the way they did. Not against a semiautomatic precision rifle, actually for it, but think the Army could have done it cheaper and better. 

As for the M14's, we got them, there paid for, rebarrel as needed and give soldiers a case of M118 and a few days on a KD range every couple of months and its done. I'm all about new cool shit, but just like the "pistol" the Army gay's the hell out of it, makes a several million(billion) dollar project out of it, and you end up with an ACU pattern uniform in the end. I'd rather spend the money on bullet's.

That said, the SDMR is basically an M16A4, with a NM barrel/trigger and free float rail. With mk262, it will shoot 1(sub) moa all day long, its cheap, easy, no retraining, and same same, case of ammo, KD range every few months and done. But it lacks the range/lethality at distance that a heavier round would offer (6.5 creed would be a good round IMHO).

As for the headshot's, I fully agree, and wonder where you were when I preached that same shit years ago and got told to shut up and color. lol I also agree with trying to CQB with a scoped M14, and would say the same for M110, SR25, etc. SDMR, toss a 45degrees off-set mount and Aimpoint micro a collapsible stock and you're GTG. But anyway this is getting too long, I didn't and I'm not saying you are wrong, things are always changing, but thought i would voice my much different experience with regards to the M14 & EBR.

$.02


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