AMMUNITION TECHNICAL COMPARISON

7.62×39mm FMJ Vs 7.62×51mm FMJ

Technical and practical comparison of two widely used full-metal-jacket rifle cartridges, covering projectile characteristics, velocity, energy, trajectory, recoil, ammunition weight and typical application.

7.62×39mm FMJ Intermediate rifle cartridge
7.62×51mm FMJ Full-power rifle cartridge / 7.62 NATO class

General Technical Comparison

Values below are representative of common military-type FMJ ammunition. Actual performance varies according to ammunition manufacturer, projectile weight, barrel length, propellant and test conditions.

Characteristic 7.62×39mm FMJ 7.62×51mm FMJ / NATO
Typical projectile 122–124 gr 145–150 gr
Typical bullet mass Approx. 7.9–8.0 g Approx. 9.4–9.7 g
Case length Approx. 38.7 mm Approx. 51.2 mm
Overall cartridge length Approx. 56 mm Approx. 71 mm
Typical muzzle velocity Approx. 700–730 m/s Approx. 800–850 m/s
Typical muzzle energy Approx. 1,950–2,150 J Approx. 3,200–3,600 J
Recoil Moderate Significantly higher
Trajectory More curved Flatter
General rifle role Short / medium range Medium / extended range
Cartridge weight Lower Considerably higher
Typical weapon platform Assault rifle / carbine Battle rifle / DMR / machine gun

Ballistic Performance

The 7.62×51mm is a considerably more energetic cartridge than the 7.62×39mm. Representative military-type loads commonly produce approximately 50–75% more muzzle energy.

7.62×39mm FMJ

Representative example: 123 gr projectile at approximately 720 m/s.

E ≈ 2,070 J
≈ 2.07 kJ

7.62×51mm FMJ

Representative example: 147 gr projectile at approximately 840 m/s.

E ≈ 3,360 J
≈ 3.36 kJ
7.62×39 Velocity 700–730 m/s
7.62×51 Velocity 800–850 m/s
7.62×39 Energy ~2.0 kJ
7.62×51 Energy ~3.4 kJ

Trajectory and Range Characteristics

The 7.62×51mm generally maintains velocity more effectively and has a flatter trajectory than the 7.62×39mm.

0–200 m
7.62×39: Excellent
7.62×51: Excellent
200–300 m
7.62×39: Very Good
7.62×51: Excellent
300–400 m
7.62×39: Increasing projectile drop
7.62×51: Strong ballistic performance
400–600 m
7.62×39: Beyond its principal rifle role
7.62×51: Maintains superior velocity and energy
600 m+
7.62×39: Not its principal design role
7.62×51: Designed for extended-range applications

Retained Energy and Barrier Performance

With comparable conventional FMJ projectile construction, the 7.62×51mm normally retains more kinetic energy because it combines a heavier projectile with greater muzzle velocity.

7.62×39mm

  • Lower overall kinetic energy
  • Lower projectile velocity
  • More rapid velocity loss over distance
  • Optimized around an intermediate-cartridge role

7.62×51mm

  • Higher muzzle energy
  • Higher projectile velocity
  • Better energy retention over distance
  • Generally greater performance against intermediate barriers

Important: FMJ describes the general projectile jacket construction. It should not be confused with specialized armour-piercing ammunition, which represents a different projectile category.

Recoil and Weapon Handling

One of the important differences between the two cartridges is recoil impulse.

7.62×39mm

  • Moderate recoil
  • Suitable for relatively compact rifle platforms
  • Generally lighter weapon systems
  • More compact ammunition and magazines

7.62×51mm

  • Significantly greater recoil impulse
  • Usually associated with heavier rifle platforms
  • Greater cartridge dimensions
  • Higher ballistic output

Ammunition Weight and Logistics

Cartridge weight becomes particularly important when large quantities of ammunition must be transported, stored or carried.

Quantity 7.62×39mm 7.62×51mm
Typical cartridge weight Approx. 16–17 g Approx. 23–25 g
1,000 rounds Approx. 16–17 kg Approx. 23–25 kg
10,000 rounds Approx. 160–170 kg Approx. 230–250 kg
100,000 rounds Approx. 1.6–1.7 tonnes Approx. 2.3–2.5 tonnes

Figures represent approximate ammunition mass only and exclude cartons, ammunition boxes, pallets and other transportation packaging.

Typical FMJ Configuration

7.62×39mm FMJ

  • Typical projectile weight: approximately 123 gr
  • Full Metal Jacket projectile
  • Common military-profile projectile designs
  • Brass or steel cartridge cases depending on manufacturer

7.62×51mm FMJ

  • Typical projectile weight: approximately 147–150 gr
  • Full Metal Jacket projectile
  • Military ball configurations widely available
  • Brass cases commonly used

General Application Comparison

7.62×39mm — Principal Characteristics

  • Lighter ammunition
  • Smaller cartridge dimensions
  • Lower recoil
  • Compact rifle platforms
  • Strong short-to-medium-range performance
  • Lower ammunition transport weight

7.62×51mm — Principal Characteristics

  • Higher projectile velocity
  • Substantially greater kinetic energy
  • Flatter trajectory
  • Better retained energy at distance
  • Full-power rifle cartridge
  • Higher ammunition and weapon-system weight

Bottom Line

7.62×39mm FMJ

Lighter, more compact and lower-recoil ammunition, traditionally associated with assault rifles and short-to-medium-range applications.

7.62×51mm FMJ

A full-power rifle cartridge offering significantly greater muzzle energy, higher velocity, a flatter trajectory and improved retained ballistic performance, at the expense of greater recoil and ammunition weight.

In simple terms, the 7.62×39mm prioritizes compactness, reduced ammunition weight and moderate recoil, while the 7.62×51mm prioritizes ballistic energy, velocity and performance at greater distances.
Technical Note: All ballistic figures shown are indicative and should not be interpreted as manufacturer-certified specifications. Actual velocity, energy, trajectory and cartridge weight depend on ammunition manufacturer, projectile construction, barrel length, firearm configuration, environmental conditions and applicable testing standard.