B36A4 vs M4A1

2012–Present

1994–Present

~20,000 estimated

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

999 mm (39.3 in) stock extended / 738 mm (29.1 in) stock folded

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

480 mm (18.9 in)

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

3.63 kg (8.0 lb) empty

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

30 rounds standard, 20/100 round options available

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

Gas-operated, short-stroke gas piston, rotating bolt

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

Single-stage, with two-stage available on some variants

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

Integrated 3x optical sight (Zeiss RSA-S) with backup iron sights or optional Picatinny rail-mounted optics

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