Why did the militayr select 14.5" Bbl length?

[general_purpose]

Why select that exact barrel length for the M4 Carbine? I mean, they could have picked any length they wanted.

Was it the most ballistically optimal length for the 5.56mm 64 grain bullet and the 1 in 7 twist(?) ? Inquiring minds want to know.

[EricCartmann]

Awesome question. I want to know too.

I got a Vietnam War books where there is a picture of a soldier carrying what looks like a M4/CAR15 type AR. So it seems like these types of weapon were available way before the M4 craze of the early 90's. I also believe the Colt Commando was available shortly after the VN war.

If I had to make an educated guess though, I would say 14.5" was chosen because it appears to be the shortest legnth possible that could be compatible with a M203.

http://www.motionpicturearmourer.com/ColtM4-M203-NSN.jpg

[DANGER CLOSE]

Shortest barrel length with the ability to mount a bayonet. the step down cut is for the m203.;)

[EricCartmann]

Shortest barrel length with the ability to mount a bayonet. the step down cut is for the m203.;)

good point. you can't mount a standard bayonet if barrel was any shorter. ;)

[panzerr]

Perhaps it was a compromise between a long barreled rifle and something smaller and more manageable, being that it was at the ass end of the 'accuracy more important than volume of fire' era? Or maybe it was meant to replace the M1 Carbine???

[Spurholder]

What DangerClose said...

[TY44934]

Sure seems like every photo from Baghdad shows our boys kicking down doors and heading into houses or huts. Plus, infantry are constantly getting into/out of armored vehicles or helicopters.

14.5 appears a lot easier to manage indoors & in vehicles than the older 20" barrel guns. But, we did just order a bunch more 20" guns.

[Ross]

The Army tried 10 and 11.5 inch barrels in Vietnam with the XM-177 series.

Colt offered the "M16A1 carbine" with a 14.5 inch barrel (lightweight) like the Isralies used for some time. This was so the standard bayonet would fit. The SP-1 Carbine was basically the commercial version with a 1.5 inch longer barrel at the end.

Many of the Army's and USAF's 10 and 11.5 inch barrelled weapons were rebarrelled over the years with Colt's 14.5 inch Carbine barrel. There's plenty of USAF photos of their GAU-5 series, and there's a pretty well-known pic of three Rangers on the Pt Salines airfield humping a M67 90mm recoiless and stuff. The gunner with the 90 laying across his ruck on his back totes a 14.5 inch rebarrel.

The 14.5 inch barrel was simply the logical barrel length for Colt to use in the XM-4 program when it came about.

While bayonet mounting might seem secondary, there are a series of other gadgets that use the same mounting system. Things like less-lethal riot control systems, and R&D systems (that have the potential for adoption) like the RAW, etc. all mount up like a bayonet. So it's logical to want that barrel length.

[Failure2Stop]

If I recall correctly, the military didn't really "pick" 14.5. The M4(in whichever Colt number was given) was originally built for a foreign military, and carried over to the M4 program.

Further, my understanding is that 14.5 is the shortest length they (Colt) could run the barrel, allowing the cartridge case to not be in the actual process of obturation during bolt unlock, and maintain 6" of barrel past the port for proper dwell time.

I am sure Scott Ryan will be able to clarify this issue.

[decodeddiesel]

This is a very interesting thread! Keep up the good work and good data!

[ABNAK]

If I recall correctly, the military didn't really "pick" 14.5. The M4(in whichever Colt number was given) was originally built for a foreign military, and carried over to the M4 program.


It was orignally called the "Abu Dhabi" carbine. (per "The Black Rifle", at the very end of the book)

[telecustom]

Ok, here is the easy explination for the 14.5 barrel. 14.5" is the shortest a 5.56mm barrel can be and still burn most of the powder and have any kind of consistant accuracy out to 600m. The 10" is loud as hell and throws a nasty flash. That's why the 10" barrels from the Vietnam Era had that 5" Flash hider. The 10" makes decent entry gun but that is about it. The 14.5" is a good happy medium between 10" (entry) and 20" (distance).

[K.L. Davis]

The 14.5" barrel was in (limited) U.S. military service on the Colt 723, and there was also the Colt 725/C8, XM4 and 727 -- sales to the UAE may have brought us the step cut for the M203, but I am pretty sure the 14.5" barrel was already around.

The reason for a 14.5" barrel is to (as already mentioned) have the proper length to mount a bayo (or other devices) on a platform using the carbine length gas system/hand guards.

Testing for burn efficiency developed the 18" SPR barrel.

[5POINT56]

Thanks for the interesting info fellas.

[KevinB]

Keep in mind Canada adopted the C-8 as a pencil 14.5 barrel based on pre-existing Colt models circa 82-84.


The 14.5" from my understanding came about from taking a CAR-15/XM-177 series gas system and adding the same length of barrel in front of the gas port as the M16 series.


As from General Purpose's intial thread a 16.5" barrel is the optimal barrel length for M855 which is 62gr not 64.

[scottryan]

The 14.5" barrel was in (limited) U.S. military service on the Colt 723, and there was also the Colt 725/C8, XM4 and 727 -- sales to the UAE may have brought us the step cut for the M203, but I am pretty sure the 14.5" barrel was already around.

The reason for a 14.5" barrel is to (as already mentioned) have the proper length to mount a bayo (or other devices) on a platform using the carbine length gas system/hand guards.

Testing for burn efficiency developed the 18" SPR barrel.


The 14.5" barrel came about in the early 1970s on the 65X series of carbines.

[K.L. Davis]

The 14.5" barrel came about in the early 1970s on the 65X series of carbines.
Roger that... I remember the 653, and Ross already pointed that out in this post.

Just pointing out that, well... a good chunk of what had been posted is wrong.

I try and do one nice thing a day ;)

[ddemis]

Just bought new BCM bolt that is MPI inspected. The ad also says "shot peened" for added strength. Can someone explain what this term means and how it strenghtens the bolt.

[MX5]

Shot peening induces metal surface strength to reduce corrosion and fatigue failure. Essentially the surface is bombarded by minute particles of steel, ceramic or glass and provides uniform surface restructuring. This will improve the surface strength and promote adhesion of lubricants. This question should probably be on it's own thread as it's not related to the 14.5 bbl IMHO.

[edlmann]

Shortest barrel length with the ability to mount a bayonet. the step down cut is for the m203.;)

Could be, but if I'm going to poke a bad guy with a knife on a stick, I want a longer stick.

[SuicideHz]

Could be, but if I'm going to poke a bad guy with a knife on a stick, I want a longer stick.

You obviously don't get it. Yes, it would be nicer to "poke him" from another 5 inches away but remember this- they were looking into a shorter barrel. They used the carbine gas system and then had to find a barrel length that would work with bayonets so bayonets wouldn't have to be remade for a new length.

[CarlosDJackal]

Ok, here is the easy explination for the 14.5 barrel. 14.5" is the shortest a 5.56mm barrel can be and still burn most of the powder and have any kind of consistant accuracy out to 600m. The 10" is loud as hell and throws a nasty flash. That's why the 10" barrels from the Vietnam Era had that 5" Flash hider. The 10" makes decent entry gun but that is about it. The 14.5" is a good happy medium between 10" (entry) and 20" (distance).

What I understand is something along these same line. The 14.5" barrel allows for minimal loss in external and terminal ballistics from the 20-inch M16s. The shorter barrel allowed for a more "manageable" rifle.

But since I am no expert in this arena, this is all based on my (fading) memory. Doc Roberts could probably give us the real reason for the 14.5" barrel.

[Submariner]

The 14.5" also permits use of m7 and M9 bayonets.

[SuicideHz]

The 14.5" also permits use of m7 and M9 bayonets.

Yes, exactly.

that's another vote for "bayonet."

[hillmillenia]

My understanding is that the 14.5" barrel is the minimum length you can go and still get the required reliability and performance. If memory serves, your still better off with a 20" bbl. but of course they lack the agility of the M4. And with all that said, I still hear much negitivity regarding performance in the arid, sandy enviroment of the middle east.:(

[coldblue]

Danger Close's response is "very close."
M4 was a designation we (USMC Development center @ Quantico, Va.) assignded to a program to replace Recon's M3A1 Grease Guns (.45 ACP SMG's). We started with Colt Commando's that had 11.5" barrels. We were happy with them as SMG's, but then the bayonet requirement latter was adressed by other potential 5.56mm SMG Marine users. To answer this, Colt re-entered with 14.5" barrels...and so it went.
By the way, real Marine M4's back then had M16A2 upper receivers.
A real collectable out there somewhere would be the orignial Marine Corps Operator Manuals that our Master Gunnery Sergrant Nicoliaision produced for this program. Unfortunately, we subsequently failed to optain Congressional funding for the M4's purchase four consecutive years in a row, and after that series of budget failures, the USMC Comptroller would not allow us to include it in our samall arms budget thereafter. About this time, the Army's 18th Airborne Corps started a campaign to replace their rifles with a similar carbine...so there goes the story.
And as Elmer Keith would say..."hell, I was there."

[SuicideHz]

So then the answer is simply because of a bayonet then...

Interesting details!

[skyugo]

so when's the military gonna adopt mid lenght gas systems? :o

[ddemis]

If I'm not mistaken the 16 inch barrel is the best compromise for ballistics,reliability and acceptable range with 5.56 ammo. The only drawback,you can't mount a bayonet.Right?

[ddemis]

And, as for the mid length gas system good luck with that just like the army adopting 6.8 rem.

[coldblue]

This is not so much a compromise for performance as it is for "civilian legal" issues.
I think Mark Westrum of the new Armalite was first to make his 16" carbines with the mid-length gas tube (Thank You, Mark). IMO, this solved more a cosmetic issue with too much barrel protruding from the traditional AR front sight/gas block than functionng issues. I mean the civilian legal 16" Colt's, etc., just did not look "right." I say this, not because I don't actually personally prefer the 16" barrels myself, but because the M4's shorter gas tube has proven itself well enough over the years, especially in semi-auto only guns.
The 16" mid-lengths also resulted in many of us buying, or building, yet another upper, or two just to have something different and thus increasing the AR's low tech popularity. This is probably one of the best reasons the AR is so popular because its so flexible and easy/simple for so many of us to work on "at home." Unlike the M1/M14 which are hardly "garage-handyman friendly.

[Failure2Stop]

M4 was a designation we (USMC Development center @ Quantico, Va.) assignded to a program to replace Recon's M3A1 Grease Guns (.45 ACP SMG's). We started with Colt Commando's that had 11.5" barrels. We were happy with them as SMG's, but then the bayonet requirement latter was adressed by other potential 5.56mm SMG Marine users. To answer this, Colt re-entered with 14.5" barrels...and so it went.

Well, that answers that, thank you for the info.