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.
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.
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.
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???
What DangerClose said…
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.
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.
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.
This is a very interesting thread! Keep up the good work and good data!
It was orignally called the “Abu Dhabi” carbine. (per “The Black Rifle”, at the very end of the book)
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).
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 not the 14.5" barrel.
The reason for a 14.5" barrel to 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" barrel of the SPR…
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.
Thanks for the interesting info fellas.
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.
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
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.
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.