The 5.56×57mm XM645 was an experimental military cartridge developed by AAI for the SPIW project.
Details[]
The XM645 is a redesign of the older XM110 round. The casing is now 4mm longer in length, while eliminating the concave bottom area of the casing structure. Early examples also implement a new single-piece piston primer, while later rounds used traditional Berdan primer caps.
Like the XM110 before it, the projectile is a steel flechette encased in a green fiberglass sabot. Later examples of the ammunition has the flechette encased in a white synthetic bale.
The casing is also used as the basis for the 5.77×52mm SBR cartridge developed for the AAI SBR weapon.[1]
Gallery[]
XM645 early variation circa 1965.
Headstamp.
XM645 later variation with synthetic bale sabot.
Headstamp.
Diagram of 5.56x57mm XM645.
Early variation of 5.56x57mm XM645 sectioned.
Flechette next to casing of of 5.56x57mm XM645 (late version).
Flechette above casings of both early and late versions of 5.56x57mm XM645.
Diagram of AAI Flechette SPIW rounds in general.
Diagram of several tracer rounds concepts for AAI's Flechette SPIW rounds in general.
See also[]
External Links[]
- XM645 on municion.org (Spanish)
- SPIW flechette on firearmsworld.net (Chinese)
- PDF on SPIW modes of fire
- PewPewPew articel on AAI SPIW rounds (Chinese)