XM8 – Lightweight Assault Rifle System


The XM8 assault rifle is a proposed replacement for the current M16 rifle and M4 carbine, the standard infantry weapons in today’s US military. The XM8 action is based upon the Heckler & Koch G36, a tried and true infantry weapon with a reputation for toughness and reliability.

The XM29 OICW project, which combined both an assault rifle and a smart grenade launcher, turned out to be too heavy, fragile, and expensive. The rifle part of the XM29 was adapted to become the XM8. The smart grenade launcher part of the XM29 is being developed separately as the XM25.



The XM8 is a developmental U.S. military designation and project name for a lightweight assault rifle system that was under development by the United States Army from the late 1990s to early 2000s. The Army worked with the small arms manufacturer Heckler & Koch (H&K) to develop the system to its requirements in the aftermath of the OICW contract, for which H&K had been a subcontractor to ATK (General Dynamics was involved in latter stages). Although there were high hopes that the XM8 would become the Army’s new standard infantry rifle, the project was put on hold in mid 2005, and was formally cancelled on October 31, 2005.


The first 30 XM8 prototypes were delivered by November 2003 for preliminary testing. Later, at least 200 developmental prototypes were procured. Among the complaints during testing were too low a battery life for the weapon’s powered sight system and some ergonomics issues. Two other key issues were reducing the weapon’s weight and increasing the heat resistance of the hand guard, which would start to melt after firing too many rounds.

The main testing was largely completed, and the Army pushed for funding for a large field test. However, in 2004 Congress denied $26 million funding for 7,000 rifles to do a wide scale test fielding of the XM8 in 2005. At the time the rifle still had developmental goals that were incomplete, primarily associated with the weapon’s weight; the battery life had been extended, and a more heat-resistant plastic hand-guard added. The earliest product brochure lists the target weight for the carbine variant at 5.7 lb (2.6 kg) with the then current prototype at 6.2 lb (2.8 kg). The weight of the carbine prototype had since grown to 7.5 lb (3.4 kg) according to a brochure released by HK and General Dynamics in January 2005.

During the same period, the Army came under pressure from other arms makers to open up the XM8 to competition. The main argument was that the weapon that was being adopted was a substantially different system than for the original competition that ATK and H&K had actually won (XM29). Other issues were that the Army has a legislated obligation to prefer U.S.-based manufacturers, and that a previous agreement with Colt Defense required the Army to involve Colt in certain small-arms programs. The XM8 program was put on hold by the Army in 2004. The exact reason why this happened is a matter of debate; some combination of the aforementioned technical issues, funding restrictions, and outside pressure being involved.

In 2005, the Army issued a formal Request for Proposals (RFP) for the OICW Increment One family of weapons. This RFP gave manufacturers six months to develop and deliver prototype weapons with requirements very similar to the XM8 capabilities, but with the addition of a squad automatic weapon (SAW) configuration. Currently, no XM8 prototypes have been shown that actually match the capabilities of the M249 (e.g. fast barrel replacement, high sustained rate of fire, belt feed). The OICW Increment One requirement for the SAW includes fast barrel replacement and high sustained rate of fire, but leaves the ammunition feed choice up to the manufacturer.


As of July 19, 2005, the OICW Increment One RFP was put on an eight-week hold, with an indication given that the program was being restructured as a joint procurement program including the Army and unnamed other branches. On October 31, 2005, the OICW Increment One RFP was canceled until further notice.

In an article in Jane’s Defence Weekly, April 26 2006 (Vol 43, page 30) we learn that “The US Army has again delayed the procurement of its future infantry weapons, this time for more than five years, and is working to field two interim guns in the meantime.”

Description and Specifications

The materials used to build the XM8 are almost entirely composites — with the notable exception of the cold hammer forged steel barrel. Preliminary tests in desert and Arctic conditions have shown XM8 to be a rugged weapon, though some complaints arose. It is reported to be capable of firing 15,000 rounds without cleaning or lubrication and up to 20,000 rounds before barrel replacement. The M16A2 needs to be cleaned often, and has a barrel life of approximately 7,000–8,000 rounds.

Internally, the XM8 uses a rotary locking bolt system that functions and fieldstrips like those used in the M16 rifle and M4 carbine. The bolt is powered by a unique gas operating system with a user-removable gas piston and pusher rod to operate the mechanism. Unlike the current M4 and M16 direct gas system with gas tube, the XM8 gas system does not introduce propellant gases and carbon back into the weapon’s receiver during firing.

While the XM8 was not exposed to battlefield conditions, it’s still a feat the current service rifle hasn’t come close to rivaling. During their Oct. 20-23 2003 trip to Germany, the weapons experts said they were impressed after watching Heckler & Koch engineers fire four high-capacity magazines, with 100 rounds apiece, in less than five minutes.

This improved reliability can be credited to differences in the XM8’s operating system from the one in the M16. For instance, a thin gas tube runs almost the entire length of the barrel in all of the M16 variants. When the weapon is fired, the gases travel back down the tube into the chamber and push the bolt back to eject the shell casing and chamber a new round. The XM8’s gas system instead is connected to a mechanical operating rod, which pushes back the bolt to eject the casing and chamber the new round each time the weapon is fired. So there’s no carbon residue constantly being blown back into the chamber, reducing the need to clean the weapon as often. You don’t get gases blowing back into the chamber that have contaminates in them. The XM8 also has a much tighter seal between the bolt and the ejection port, which should cut down on the amount of debris that can blow into the weapon when the ejection port’s dust cover is open.



  • Caliber: 5.56 mm
  • Cartridge: 5.56 x 45 mm NATO
  • Weight: 6.4 lbs | 2.8 kg empty
  • Designed: 2002
  • Produced: 2003 — 2004 (prototypes only)


Variants of XM8

The XM8 is a modular weapon that can be adapted to different roles fairly easily. It can use any of four barrel sizes: 9″, 12.5″, 20″, and heavy 20″.

The 12.5″ barrel is the standard set-up, and with the adjustable buttstock, makes the Baseline Carbine variant. With the stock fully extended, it is 33″ long, the same as an M4 (which has a 14.5″ barrel). It weighs in at about 6.4 lbs, with a goal of being reduced to 5.7 lbs. The M4 with comparable accessories weighs nearly 9 lbs. The picture above shows an XM320 side-loading detachable grenade launcher mounted.

The 9″ barrel makes the weapon a submachinegun-like personal defense weapon (called the Compact Carbine) that would be ideal for vehicle crews. Also, it seems to be that Special Forces types would find it useful for urban raiding missions and the like. With the buttcap (as pictured on the right, second from the top) it is less than 21″ long overall.

There are two versions of the 20″ barrel. There’s a standard weight match-grade unit for sharpshooter work and a heavy-duty machinegun unit with a folding bipod for use as a sustained fire automatic rifle.




See XM8 in action (YouTube video) »


Heckler & Koch

Engineering work was done at facilities in the United States and Germany by H&K, General Dynamics and ATK.

[via Murdoc Online.com, GlobalSecurity.org & Wikipedia]

Google Bookmarks Digg Reddit del.icio.us Ma.gnolia Technorati Slashdot Yahoo My Web

25 Responses to “XM8 – Lightweight Assault Rifle System”

  1. That’s pretty hot. I’ve seen it before and been have been tempted to buy one every since!

  2. Yeah, I wish I had this toy :)

  3. It is very interesting for the product , but it is very encouraging for modernization and abilities for its operational functions.

    As an engibeer and security personnel It is good to have a better look or actually visit the company.

  4. This weapon looks like it could kick the crap out of the M-16. I have nothing against the M-16 because i am a fan of the M-16. This weapon will prove its self on the battle field sooner or later.

  5. Very futuristic-looking – but I’m not convinced about retaining accuracy in autofire without the bullpup configuration. Is the faster reload advantage from a forward magazine worth lower accuracy?

  6. this rifle is the shit its super light weight
    and very easy to aim and it is lighter than the C7A1’s(M16)
    buy far the Canadians got some of them and i traded my C8A1 Carbine
    (M4A1) in for the M8 its fucking amazing weapon

  7. HMMMMMMMMMM yer Jordan thats BS beccause no1 uses the XM8

  8. where can these be bought?

  9. shooting clothing on March 19th, 2009 at 3:30 am

    Always good quality info from this site!

  10. This is the weapon im getting issued with in 2011 they announced that we are supposed to turn in our M-16s and pick up the XM8-Assualt system in the Weapons holds cant wait this bad boy shot through a cement wall over at fort benning

  11. Hey DAKOTA, I find your comment most interesting. Can ANYONE tell me how come this Dakota (presumably a US soldier) is posting a comment in 2009 about how his unit is getting the XM8 in 2011 when all sources; official and independent, tell me the weapon has been shelved since 2007?

    If what Dakota said is true, I really would like to know more. DAKOTA, if youre reading this, please reply to this. If anyone else knows about this please reply.

  12. this thing has no rails to atach things to >.>

  13. It has hardpoints instead. you don’t have to re-adjust the attachements because of how they are hooked on. See the ovals on the front of the gun? that is were they attach.

  14. haha good joke private (that is if you’ve even gone through basic yet) dakota. if someone told you this they are ill-informed or playing a joke. and if you’re still using an m16 your probably getting issued an m4 as almost all of our armed forces are still transitioning to the m4 with the exception of a few Marine infantry units as well as grenadiers.

  15. this weapon just reminds me of the g36, just a slender version of it, i dont know if anyone else has noticed this, does anyone else agree with me may be

  16. Tom, yes, the xm8 is modelled after the G36 weapon line.

  17. spc deemer andrew on August 24th, 2010 at 1:18 pm

    well in any case if it does get adopted within the ranks of the army, it will be better then the m16 for the simple fact that you dont have to clean it as much. and hopfully im in when it happens. hell i dont get out until 2014.

  18. […] the M4, and another for a rapid-firing grenade launcher, Program XM29, which ended up with the XM25. Along the way, the program ran into more corporate and political interference than you can […]

  19. I don’t understand why the military hasn’t adopted this weapon. It seems much nicer than the M4.

  20. The smaller Nato calibre might be out, the US spec forces are choosing HK 417 and even AK’s in the field, the M16-M4’s should be the past too many jamming issues and constant cleaning, soldiers are not confident with them which means low morale.

  21. I hope the US takes this as new weapon, dump the M16, M4 trash. Its long overdue to rid the Mattel toys from the military.

  22. Hey does anyone know which is better? The Tar-21 or the xm8?

  23. The XM8 is a great weapon system and even though I’m only a teenager, I would love to be able to purchase this weapon when I join law enforcement in my later years. I honestly believe that H&K should either get this rifle back into production (at least for the civilian market) or sell the design to a different company (ex. Robinson Armament, Bushmaster, Remington Defence, etc.) so they can start producing them. It would be nice to hear about the XM8 making a come-back. Sure the XM8 had some flaws, but look at the original M16, it jammed a lot but did Colt just give up on it? No, they kept going with it and look where the M16 is now, it’s been the main in-service rifle for almost 60 years. I hope my suggestions get taken into consideration.

  24. I don’t understand, is this rifle going to be released soon, or is it a dead project? I hope the US takes this rifle on as the new in-service weapon.

  25. Hey, has anybody heard of the new XM9? I don’t know if it’s real or fake…. Would appreciate feedback.\