M4A1 vs SOR-556 Mk2

1994–Present

2004–present

~10,000,000+ units (including all variants and licensed production)

838 mm (33.0 in) stock extended, 756 mm (29.8 in) stock collapsed

29.5–39.8 in (749–1011 mm)

368 mm (14.5 in) standard; 406 mm (16 in) for the M4A1 SOPMOD variant

10 to 18 inches

3.07 kg (6.8 lb) empty, 3.74 kg (8.2 lb) with full 30‑round magazine

3.29–3.5 kg (7.3–7.7 lb)

30 rounds standard STANAG, 20‑round low‑profile, 40‑round drum, 60‑round Beta‑C‑Mag available

30-round STANAG

Short‑stroke gas piston (M4A1 variant) with rotating bolt; original M4 uses direct‑impingement

Short-stroke gas piston, rotating bolt

Two‑stage military trigger, full‑auto only selector on M4A1; semi‑auto on standard M4

Standard: A2 front post and rear flip‑up aperture; optional: MIL‑STD-1913 Picatinny rail for aftermarket optics, tritium night sights, or holographic sights

Flip-up iron sights or optics