AR-15 vs M4A1

1964–Present

1994–Present

12,000,000+ units (combined military, law‑enforcement, and civilian production)

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

840 mm (33.1 in) with stock extended (16 in barrel), 730 mm (28.7 in) with stock collapsed (14.5 in barrel)

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

406 mm (16 in) standard, 368 mm (14.5 in) carbine, 508 mm (20 in) designated marksman, 254 mm (10 in) pistol‑length

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

3.2 kg (7.1 lb) empty (16 in barrel, without optics)

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

30 rounds standard, 10/20/40/60 round options, drum magazines up to 100 rounds

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

Direct‑impingement gas system (original) or short‑stroke gas piston (aftermarket/variant), rotating bolt, semi‑automatic or select‑fire

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

Single‑stage semi‑automatic trigger; military select‑fire models use a two‑stage fire selector with safe, semi, burst, and automatic modes

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

Standard: detachable flip‑up rear iron sight and fixed front post; many models equipped with Picatinny rail for optical, holographic, or night sights

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