The M4 carbine has an interesting history that is worth relating, so here goes:

In 1966 a requirement developed in the US Army for a shortened version of the M16, primarily for use by Special Forces who needed a smaller weapon for covert use, e.g. Long Range Reconnaissance Patrols (LRRPs).  This involved jumping into jungles and so forth where a long rifle could easily be bent and was too heavy.  Colt's developed a derivative of the M16 that was initially called the XM177, that differed from the original M16 in that it had a ten inch barrel with a long flash suppressor that incorporated expansion chambers to reduce the deafening muzzle blast from the short barrel, a telescoping stock, and a redesigned round handguard held in place with a wedge-shaped slip ring to allow easier removal of the handguard halves for maintenance.  A version with the forward bolt assist favoured by the Army was called the XM177E1.  Together they were known as the "CAR-15" project, and that was the name many of the troops called them in Vietnam, although the guns were often stamped "Commando", and they are often called the Colt Commando as well.

Only a few thousand of these guns were made, due to serious problems with them.  The muzzle blast was still deafening and blinding even with the clever flash hider/suppressor, bullets would yaw and "keyhole" when hitting the target (because of insufficient stabilisation, apparently, and also debris clogging the suppressor), the cyclic rate was all over the place due to inconsistent gas pressure at the gas port (because the gas port was so close to the muzzle) and so on.

Colt redesigned the XM177 and XM177E1 into the XM177E2 which had certain improvements such as a slightly longer 11.5 inch barrel, but it too suffered from the same problems and the Army ditched the project.  Undeterred, Colt's tried to sell the XM177E2 abroad, but the Bureau of Alcohol, Tobacco and Firearms had classified the flash hider as a sound suppressor, and in a bid to stop terrorists (supposedly, more likely the Israeli Mossad) from acquiring silencers the US Govt. banned their export, inadvertently stopping Colt's from being able to sell the XM177E2 abroad.  The picture shows a close-up of the end of the newer 11.5 inch barrel, note the unusual washer used to lock the flash suppressor in place:





A 1/9 twist does make vastly more sense on a gun like this, because it essentially replaces the submachinegun that tankers used to be issued with.  It is far more likely to be fired continuously in burst-fire mode than an M16A2 rifle carried by a rifleman would be.  The slower rifling twist means slower bore erosion (as there is less resistance to the bullet going down the barrel).  Bore erosion is exacerbated by continuous full-auto fire (because the metal of the barrel gets softer as it heats up).  However, military-issue M4s come with the same 1/7 twist as the M16A2, which


leads to faster bore erosion.  The official explanation for this is that the 1/7 twist is needed for the longer tracer round, however there is no real need for the tracer to be fired from the M4, and frankly at the short ranges the M4 is likely to be used, the tracer fired from a 1/9 twist will not be that far from the point of impact of the standard ball round.  Colt's tried to impress this point on the US Dept. of Defence when the M16A2 was adopted, but were rebuffed.

Bushmaster Firearms entered the scene during Operation Desert Shield.  With the imminent prospect of war, the military suddenly found themselves with a large demand for rifles.  Many Army units were still armed with the M16A1, the replacement of which had only begun in 1986.  With a large demand for M16A2s and M4s both from the US forces and allied forces, the Dept. of Defence approved a contract to buy M4 carbines from Bushmaster Firearms of Maine.  Bushmaster supplied 4,000 M4 carbines to the US Army, these were deployed by the 82nd Airborne Division during Desert Shield and Desert Storm, reportedly being used by Gen. Schwarzkopf's bodyguards at one point.

where did you source this from?

AGNTSA...

Quoted: ..., however there is no real need for the tracer to be fired from the M4, and frankly at the short ranges the M4 is likely to be used, the tracer fired from a 1/9 twist will not be that far from the point of impact of the standard ball round.  Colt's tried to impress this point on the US Dept. of Defence when the M16A2 was adopted, but were rebuffed... img.photobucket.com/albums/v205/dcobra23/barrel.jpg

Totally not true.  Colt had almost nothing to do with the 1:9/1:7 issue during the M16A2 development.  They were ready to build the gun any way we wanted it.  The only M16A1E1 barrels they built for our USMC program were in 1:7 and 1:12 for comparision testing purposes of the new barrel  profile and ammo interoperability issues.  To say that they were "rebuffed" makes it sound like they were out there marketing the idea.  They were not.  The 1:7 over 1:9 was our Marine Corps decision and was based on interoperability with NATO and the potential for future growth potential..like the Mk 262 turned out to be.

www.cybershooters.org/dgca/bushmaster_m4.htm

Quoted: where did you source this from?

unless all the resourcesi looked into was really wrong or the article is misinforming.



the ring on the xm177's moderator is refered to as the grenade ring and the one shown in the picture is backwards.

the bevel side facing the moderator




retro pic thread

total silence

uxb's xm build thread

During my short 5 month tenure in VietNam during the "scaling down" days in the first part of 1973, I was primarily a non-uniformed "desk jockey" at Long Binh. Since the base had already been turned over to the ARVN and there were few (if any) US combat troops there, we were responsible for our own security. My issue weapon was a CAR-15 with which my initiation/zeroing session was a trip to the local PDO destruction dump and involved burning through a few mags (20s) of ammo.  I had no problems and fired several mags through it at least once a day at the dump (we were destroying "articles" of concern ).

Loud, yup. Worked every round, yup. Accurate, full auto at less than 50 meters - WGAS

There is so much wrong with that story I don't know where to start. The only part that is even close to correct is the first paragraph.

Edited to say I checked the link and it appears that the above post is a cut and paste job that puts some info out of context. The information in the link is for the most part accurate, except for the 1\9 twist info.

I thought so . When I received it from someone in an email I said I must post it and let the experts deal with it.

Quoted: There is so much wrong with that story I don't know where to start. The only part that is even close to correct is the first paragraph. Edited to say I checked the link and it appears that the above post is a cut and paste job that puts some info out of context. The information in the link is for the most part accurate, except for the 1\9 twist info.

Totally not true.  Colt had almost nothing to do with the 1:9/1:7 issue during the M16A2 development.  They were ready to build the gun any way we wanted it.  The only M16A1E1 barrels they built for our USMC program were in 1:7 and 1:12 for comparision testing purposes of the new barrel  profile and ammo interoperability issues.  To say that they were "rebuffed" makes it sound like they were out there marketing the idea.  They were not.  The 1:7 over 1:9 was our Marine Corps decision and was based on interoperability with NATO and the potential for future growth potential..like the Mk 262 turned out to be.

I wrote that article, and it was well-sourced.  My understanding is that there were throat erosion problems with the 1/7 twist barrels (and I have a good source for that) and Colt's recommended the 1/9 twist (which is also mentioned in various articles), and in the end Colt's improved the metallurgy for the 1/7 twist barrels (which is not just from written sources, my own personal experiences support that) after they were unable to convince the military that the 1/9 twist was a better idea.

Of course they were willing to make the gun any way the USMC wanted it (I'm sure they would have made it pink if asked), that wasn't the point I made in the article, Colt's preferred the idea of a 1/9 twist.  Given that on the civilian/LE guns they did actually use 1/9 twists pretty extensively that seems to support the view that they preferred it (else why tool up for it, you can shoot 55gr bullets fine through 1/7?)

It certainly is the case that the 1/7 twist was adopted so that it would stabilise the very long SS110/M856 tracer bullet.

As for the XM177, most of that I sourced out of the "Black Rifle" which is considered pretty authoritative, and also I got some of it from a guy I know who was in LRRP in Vietnam.

Quoted: Bushmaster Firearms entered the scene during Operation Desert Shield.  With the imminent prospect of war, the military suddenly found themselves with a large demand for rifles.  Many Army units were still armed with the M16A1, the replacement of which had only begun in 1986.  With a large demand for M16A2s and M4s both from the US forces and allied forces, the Dept. of Defence approved a contract to buy M4 carbines from Bushmaster Firearms of Maine.  Bushmaster supplied 4,000 M4 carbines to the US Army, these were deployed by the 82nd Airborne Division during Desert Shield and Desert Storm, reportedly being used by Gen. Schwarzkopf's bodyguards at one point. img.photobucket.com/albums/v205/dcobra23/barrel.jpg

This part of the story was generated by Bushmaster marketing and turned out to be false.

At the time it was because of tracer rounds, but as it turns out 1:7 was the best choice -- as we now know that 75/77 grain is the best ammo.

1:9 can only do 69 grain or less with lead ammo.

Would not be surprised that a bunch of that came out of a Duncon Long book.  That is the best source I know of for AR tripe.

pretty sure I would listen to coldblue on this

I imagine I know what testing and documents you are refering to, and that test occured some time after the adoption of the rifle... I once posted on here concerning the results and that according to the test "the 1/7 inch twist rate promotes faster throat errosion" -- you would have thought I had two heads for even suggesting it!

The numbers are not earth shattering however and the mechanics behind it are a bit lofty for many, in all but the most etreme cases the life of the barrel is shortened by such a small amount that, as I put it earlier, most users will have ruined the barrel by improper or over-cleaning before they shoot it out one way of the other.

As I understand (from people other than coldblue) the decision to go with 1:7 was largely due to its use already with other NATO countries... as to why they chose it, that is pretty obvious if you look at the situation.

Quoted: Bushmaster Firearms entered the scene during Operation Desert Shield.  With the imminent prospect of war, the military suddenly found themselves with a large demand for rifles.  Many Army units were still armed with the M16A1, the replacement of which had only begun in 1986.  With a large demand for M16A2s and M4s both from the US forces and allied forces, the Dept. of Defence approved a contract to buy M4 carbines from Bushmaster Firearms of Maine.  Bushmaster supplied 4,000 M4 carbines to the US Army, these were deployed by the 82nd Airborne Division during Desert Shield and Desert Storm, reportedly being used by Gen. Schwarzkopf's bodyguards at one point.

This can be picked apart just by looking at the time line.  

First we shall shoot holes in the idea that the US Army was desperate for small arms because of the Kuwait invasion, and thus had to turn to Bushmaster for help.  Iraq did not invade Kuwait until August of 1990, the carbines in question were delivered in June that same year.  At the time FN was producing the M16A2 and Colt's assembly line was largely idle, and had been since they lost their M16A2 contract in 1988.

The TDP that details the M4 Carbine was not available to the US Government and thus not available to Bushmaster in 1990.  Colt first delivered the M4 TDP to the Government in 1996.

Secondly, any time you hear "in use by Navy SEALs", or "Delta" you should automatically assume bad info to follow.  Here is a picture of what was actually used, it is the same Colt Govt Carbine in common use at the time:

i36.photobucket.com/albums/e30/captcarbine/Historical/0aPSD.jpg
hosted by captrichardson

Quoted: Quoted: Bushmaster Firearms entered the scene during Operation Desert Shield.  With the imminent prospect of war, the military suddenly found themselves with a large demand for rifles.  Many Army units were still armed with the M16A1, the replacement of which had only begun in 1986.  With a large demand for M16A2s and M4s both from the US forces and allied forces, the Dept. of Defense approved a contract to buy M4 carbines from Bushmaster Firearms of Maine.  Bushmaster supplied 4,000 M4 carbines to the US Army, these were deployed by the 82nd Airborne Division during Desert Shield and Desert Storm, reportedly being used by Gen. Schwarzkopf's bodyguards at one point. This can be picked apart just by looking at the time line.   First we shall shoot holes in the idea that the US Army was desperate for small arms because of the Kuwait invasion, and thus had to turn to Bushmaster for help.  Iraq did not invade Kuwait until August of 1990, the carbines in question were delivered in June that same year.  At the time FN was producing the M16A2 and Colt's assembly line was largely idle, and had been since they lost their M16A2 contract in 1988. The TDP that details the M4 Carbine was not available to the US Government and thus not available to Bushmaster in 1990.  Colt first delivered the M4 TDP to the Government in 1996. Secondly, any time you hear "in use by Navy SEALs", or "Delta" you should automatically assume bad info to follow.  Here is a picture of what was actually used, it is the same Colt Govt Carbine in common use at the time: i36.photobucket.com/albums/e30/captcarbine/Historical/0aPSD.jpg hosted by captrichardson

good points, Ekie.

But the "Bushmaster put up 3,000 M4 carbines for GW1", is as old as the internet. And it has been repeated so often- many have accepted it as fact.

As for the comment re: "the next words to follow Navy SEAL or Delta Force are usually lies" is so true its laughable.

But ironically, the photo you referenced from captrichardson, looks like a carbine configuration that has been seen in snake-eater's hands during the Mogadishu 'problem'..............

But I love the metaphor.

Quoted: Totally not true.  Colt had almost nothing to do with the 1:9/1:7 issue during the M16A2 development.  They were ready to build the gun any way we wanted it.  The only M16A1E1 barrels they built for our USMC program were in 1:7 and 1:12 for comparision testing purposes of the new barrel  profile and ammo interoperability issues.  To say that they were "rebuffed" makes it sound like they were out there marketing the idea.  They were not.  The 1:7 over 1:9 was our Marine Corps decision and was based on interoperability with NATO and the potential for future growth potential..like the Mk 262 turned out to be. I wrote that article, and it was well-sourced.  My understanding is that there were throat erosion problems with the 1/7 twist barrels (and I have a good source for that) and Colt's recommended the 1/9 twist (which is also mentioned in various articles), and in the end Colt's improved the metallurgy for the 1/7 twist barrels (which is not just from written sources, my own personal experiences support that) after they were unable to convince the military that the 1/9 twist was a better idea. Of course they were willing to make the gun any way the USMC wanted it (I'm sure they would have made it pink if asked), that wasn't the point I made in the article, Colt's preferred the idea of a 1/9 twist.  Given that on the civilian/LE guns they did actually use 1/9 twists pretty extensively that seems to support the view that they preferred it (else why tool up for it, you can shoot 55gr bullets fine through 1/7?) It certainly is the case that the 1/7 twist was adopted so that it would stabilise the very long SS110/M856 tracer bullet. As for the XM177, most of that I sourced out of the "Black Rifle" which is considered pretty authoritative, and also I got some of it from a guy I know who was in LRRP in Vietnam.

If you spoke with Mr. Harold Waterman (if he is still alive) who worked at Colt in the 80's and was the lead engineer on the A2, then you got some straight scoop.  However, all the others that actually knew anything are gone, like Rob Roy (rest his soul).
Colt did almost no in-house testing, and none that would have gone as far as to develop throat erosion.  The 6 prototype M16A1E1's fired at Aberdeen all went to 12,000 rounds and still met the Mil-Spec.  That was the most definative test done during that period.  Colt never even visited Aberdeen during that period and any information they gleaned from the Government's efforts were provided by us.
The only issue we discovered with the 1:7 was poorer than normal "accuracy" with .22 rim fire adapters.
If Colt ever discovered 1:7 issues with erosion it was after I left the scene at the end of 1983.  Perhaps they were trying less expensive solutions to what Harold Waterman initially developed for us Marines in the original prototype 1:7's, and then the 40 or so Operational Test weapons.  I don't know, anything could have happened later.
Fact is we started with the 1:7 and continue in that twist today (thank you Mk 262).  Lets not twist the facts with what people who were not there and/or not involved think they know or remeber.  They just don't know what they don't know.  Then there are those of us who do know, but are too busy to ghost write for others.
Dan Shae (Machine Gun News March 1996) has been the only writer to get it right.  And that is because he came down here and invested some time and professionalism.