Translation: the M4 barrel is so unreliable that special operations forces units need to swap it out with a barrel from a different gun -- and one that actually works in real combat conditions.

At the end of July, SOCOM announced it had awarded Sig Sauer a contract for its suppressed upper receiver group, or “SURG,” to pair with the M4′s lower receiver.

The distinguishing features of an M4 are a flat-top Picatinny rail upper receiver for mounting an optical sight; a quad-rail Picatinny fore-end for mounting accessories; a collapsible stock; and a ...

The innovative SHRIKE 5.56 upper receiver is designed to fit any MIL-SPEC quality AR-15/M16/M4-type lower receiver and features a dual-feed system, allowing users to configure the SHRIKE 5.56 from ...

However, instead of being mated to an M4 carbine, it's designed to be used with civilian semi-automatic AR-15-type rifles, though still offering considerable improvements over the standard upper ...

It is not known what receiver has been selected, but Sig Sauer offers several models of suppressed M4-style rifle. Suppressors reduce muzzle blast and noise, making it more difficult to find the ...

Currently Raiders use an M4 lower receiver, which is the trigger and housing, attached to a SOCOM-issued upper receiver, or barrel and bolt.

Army engineers and scientists optimized the EPM to work with the M4/M4A1, M16 rifle, and standard military 5.56mm small arms round, the M855A1. The M855A1, known also as the Enhanced Performance ...

The U.S. Army could have this new carbine by replacing the upper receiver on existing M4s with a HK 416 upper receiver chambered in 6.5-millimeter Grendel.