The Diemaco M203A1 is a development of the M203 40x46mm low velocity grenade launcher. The M203 was initially developed by AAI to replace the Colt XM148 which proved overly complex when tested in Vietnam.
The Diemaco M203A1 improves on the earlier launcher by incorporating its sight into the mount rather than being atached to the top of the barrel. The Diemaco M203A1 should not be confused with the Colt-manufactured M203A1 in US service. The Diemaco launcher is offered alongside the C7 and C8 rifles made by Diemaco (now Colt Canada).
Diemaco developed the M203A1 so it has a longer action, with the breech opening further to allow the firing of all 40×46 mm LV grenades including less than lethal baton rounds. It can also be mounted on all AR-patterned rifles as well as the Steyr AUG.
Like the original M203 the launcher can be operated by either a left or right handed users. The original model had an iron sight assembly has dual azimuth adjustment knobs and an elevation dial, this model, however, has a simplified tangent sight. Diemaco stated that the M203A1 has a maximum effective range of 400m (440 yd) with a muzzle velocity of 78 m/s (260 ft/s).
The M203A1 was tested by the UK’s special forces in the late 1990s, when they evaluated the Diemaco SFW carbine, which was subsequently adopted as the L119A1. The Heckler & Koch M320 GLM (HK AG36) has since been adopted by the British Army.
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Specifications (From Diemaco Brochure):
Calibre: 40 mm
Loaded Weight: 2.15 kg (4.74 lb)
Empty Weight: 1.85 kg (4.08 lb)
Overall Length: 318 mm (12.52 in.)
Barrel Length: 228.6 mm (9 in.)
Overall Height: 140 mm (5.51 in.)
Rifling: Right Hand Twist – 6 Lands
Rate of Twist: 1 turn in 48 in. (121.9 cm)
Bibliography:
Diemaco M203A1 Product Brochure, Diemaco/Colt Canada, c.2000
Diemaco M203A1 for SFW carbine, Royal Armouries, (source)
The Armourers Bench 
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