Technical notes
How to read a V50 figure, and what STANAG 2920 is for
V50 is the most frequently misread number in a ballistic fabric specification. It looks like a protection level and it is not one. STANAG 2920 is the NATO test method that defines how the figure is obtained.
The method in one paragraph
STANAG 2920 is a NATO test method for measuring the ballistic protection of materials against fragments. It defines how V50 is obtained: the velocity at which half the shots pass through the sample and half are stopped. Shots are fired at a range of velocities, and the figure is derived from where the boundary between penetration and stop sits. It is a property of the material at a given areal density, established by a repeatable procedure.
V50 is not a protection level, and not a pass or fail
This is the point worth being blunt about. A protection level such as NIJ 0101.06 Level IIIA is a threshold: a specified panel is shot with a specified round at a specified velocity, and it either meets the requirement or it does not. V50 has no threshold in it at all. It is a comparison figure, telling you where a material sits relative to another material tested the same way. Reporting a V50 says nothing about whether a finished panel would pass any given standard, and a fabric with a higher V50 is not automatically the right fabric for your specification.
Comparing two V50 figures fairly
V50 compares materials at equal areal density. That qualifier is the whole game. Any material will stop faster projectiles if you use more of it, so a V50 quoted without the areal density it was measured at is not a comparable number, it is a marketing number. Before comparing two figures, check three things: the areal density of each sample, the projectile each was tested with, and the test method each followed.
Temperature is worth asking about as a fourth. Ballistic materials do not all behave the same way when hot or cold, and a figure measured at room temperature does not automatically hold at 60 degrees C or below freezing.
Our own V50 figures, stated in full
We publish three, and each is given with the conditions attached rather than as a bare number.
- • SB166-225: 13 layers at 3.0 kg/m2 measured 480.17 m/s against 9mm FMJ 124 grain, measured by the China Ordnance Equipment Test Center in October 2021, at room temperature. Six valid rounds between 466 and 498 m/s.
- • SB160: approximately 580 m/s against a 17-grain (1.1 g) FSP at 5.3 kg/m2, tested to GJB4300A-2012 or STANAG 2920.
- • SB130: approximately 600 m/s against a 17-grain (1.1 g) FSP at 5.3 kg/m2, tested to GJB4300A-2012 or STANAG 2920.
- • The SB166-225 figure is measured against a 9mm bullet rather than a fragment simulating projectile, so it is not directly comparable with the two FSP figures above it. Comparing across projectile types is exactly the mistake this note is written to prevent.
The note on GJB4300A-2012 covers the fragment threat these figures are usually quoted for. For a protection level with a pass or fail threshold rather than a comparison figure, the NIJ 0101.06 note is the one to read.