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Colt XM148 UBGL

Experimental Under-Barrel Grenade Launcher (1966)

Infantry Small Arms / The Warfighter

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Jump-to: Specifications

The XM-148 from Colt Firearms existed in experimental form during the Vietnam War years - it did not see widespread adoption.

Authored By: Staff Writer | Last Edited: 05/12/2021 | Content ©www.MilitaryFactory.com | The following text is exclusive to this site.
The M79 "Bloop Tube" was the primary weapon of the American grenadier during the Vietnam War (1955-1975). The weapon gave excellent service for its role of close-in fire support but, since it remained a stand-alone weapon by design, the operator was required to carry a secondary weapon for self-defense - typically a pistol with limited engagement range and man-stopping power. Nevertheless, its greatest asset was the capability to fire various warhead types through 40x46mm projectiles including smoke, flechette and anti-personnel through direct-line-of-sight or indirect-line-of-sight engagement.

During the conflict there grew interest on the part of the U.S. military to develop a better alternative. Colt's Karl R. Lewis responded in 1964 with what became the "XM148" single-shot system intended for mounting under the barrel of a standard service rifle. The weapon, drawn up and prototyped in less than 50 days, fielded a weight of 3lb with an overall length of 16.5 inches. The cartridge type remained the 40x46mm grenade with a rated muzzle velocity of 247 feet per second and maximum range out to 437 yards. A quadrant sighting device was fitted for ranged accuracy.

U.S. military authorities appreciated the type enough to order 20,000 examples and these became available to select troopers before the end of 1966. It was used operationally by both American and Australian special forces into 1967 but, before the end of the year, inherent deficiencies in its design were readily noted - the XM148 relied on multiple small parts and its trigger arrangement was such that it could be prone to accidental discharge when the trooper was on the march through the jungle. These issues led to the launcher being removed from service - the cost of a hasty prototyping and development period.

The XM148 was officially superseded by the well-received AAI M203 40mm Under-Barrel Grenade Launcher (UBGL) which is still in widespread service today (2016) though stocks of the earlier weapon remained in training roles for a few decades longer.


Service Year

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United States


Experimental Under-Barrel Grenade Launcher

Colt Firearms - USA
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(OPERATORS list includes past, present, and future operators when applicable)
Fire Support
Capable of suppressing enemy elements at range through direct or in-direct fire.
Special Forces
Qualities of this weapon have shown its value to Special Forces elements requiring a versatile, reliable solution for the rigors of special assignments.

Overall Length
419 mm
16.50 in
Barrel Length
254 mm
10.00 in
Empty Wgt
2.98 lb
1.35 kg

Quadrant Sight.


Single-Shot; Reusable

(Material presented above is for historical and entertainment value and should not be construed as usable for hardware restoration, maintenance, or general operation - always consult official manufacturer sources for such information)



Sample Visuals**

Graphical image of a 40mm grenade cartridge
Rounds / Feed

Single-Shot; Reusable
Cartridge relative size chart
*May not represent an exhuastive list; calibers are model-specific dependent, always consult official manufacturer sources.
**Graphics not to actual size; not all cartridges may be represented visually; graphics intended for general reference only.
Max Eff.Range
800 ft
(244 m | 267 yd)
Muzzle Velocity
250 ft/sec
(76 m/sec)

XM148 - Base Series Designation; introduced in late-1966 and removed from service as soon as late-1967; as many as 20,000 units produced.

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