Oehler ballistic chronographchamber pressure measurementballistic coefficientOehler Model 35P

Ballistic Velocity and Chamber Pressure Measurement

From muzzle velocity and downrange time of flight to the pressure-time curve: replace catalog values with measured data and build interior and exterior ballistics capability in the ammunition lab.

Skyscreen III screens and System 89 set up on a range

In short

Ballistic measurement in ammunition labs and on ranges works on two levels. Exterior ballistics needs trustworthy muzzle velocity and downrange time of flight to derive a measured ballistic coefficient; interior ballistics needs the pressure-time curve and peak chamber pressure. The Oehler Model 35P uses three Skyscreen III screens and two timers to produce two independent velocity readings for every shot and cross-checks them automatically. The Model 36 runs on USB power and covers velocity, rate of fire and coefficient of restitution. System 89 and System 88 extend measurement to downrange targets and spans of several kilometers, and System 85 records two pressure channels together with muzzle velocity. Evencat supplies and quotes Oehler Research products; the system-class models require an export assessment.

Two levels of measurement: exterior velocity, interior pressure

Ammunition acceptance and development need two kinds of data. Exterior ballistics looks at the projectile after it leaves the muzzle: muzzle velocity, shot-to-shot consistency, and the velocity decay along the flight path. The decay is what determines the measured ballistic coefficient, as opposed to the catalog value. Interior ballistics looks at what happens before the projectile leaves the muzzle: chamber pressure versus time, peak pressure, time to peak and rise time, all of which bear directly on safety margin and propellant lot consistency.

Both share one prerequisite: every data point must be able to verify itself. A velocity reading that looks plausible but is wrong grows into tens of meters of impact error once it enters the ballistic solution.

Trustworthy muzzle velocity: Model 35P and Model 36

The Oehler Model 35P is regarded in the industry as the gold standard of ballistic chronographs, not just because it measures velocity but because it knows whether the velocity can be trusted. Three Skyscreen III screens and two timers give every shot two independent velocity readings, and the patented PROOF CHANNEL™ compares them automatically and flags any disagreement beyond a reasonable margin. With the 4 ft mounting rail, typical accuracy is 0.25%. The built-in printer uses plain paper and ordinary ink, so results are printed and kept on the spot.

The Model 36 takes power and communication over a single USB cable and runs from a Windows PC. It covers three measurements: standard velocity, machine gun rate of fire (up to 6,000 rounds per minute, up to 400 rounds per burst) and coefficient of restitution (COR) for sporting equipment. Reports are generated automatically as PDF and raw timing data exports to Excel. Labs usually pair it with Model 57 infrared screens; outdoors, Skyscreen III.

Sensors: why Skyscreen III

Skyscreen III uses scattered skylight as its background and triggers when the projectile shadows it, so no power or lighting has to be run to the sensors on an outdoor range. The polycarbonate body withstands muzzle blast at the .50 BMG level and mounts tool-free with a single 1/4"-20 screw. The orange translucent diffuser improves trigger sensitivity in low light such as overcast days and early or late hours, the top cover suppresses midday glare, and improved cable shielding reduces false triggers from static and electrical interference. Shipped with Oehler instruments since 1984, it is the standard sensor for outdoor chronograph work.

Downrange time of flight and measured ballistic coefficient: System 89 and System 88

Downrange acoustic target set up on a range — System 89 downrange acoustic target

The ballistic coefficient is not a constant; it changes as velocity decays, so measuring near the muzzle alone is not enough. System 89 BC Chrono™ captures muzzle velocity with three Skyscreen III screens at the firing point, while four microphones at the target locate the projectile's arrival time by acoustic triangulation. Dividing one by the other gives the measured BC for this rifle and this lot, with support for G1, G7 and custom drag functions. Both controllers carry built-in lithium batteries and radio modules, so setting up needs no cabling.

When multiple measurement points are needed across spans of several kilometers, System 88 forms a GPS-synchronized measurement network from 2 to 4 identical wireless controllers, capturing muzzle velocity, time of flight at each station and impact coordinates at the same time, with microsecond timing and centimeter-level target location. The included Extended Range Truing software merges multiple tests into a single corrected ballistic solution.

Chamber pressure: the System 85 pressure-time curve

Pressure-time curve recorded by System 85 — Pressure-time curve

System 85 is the workhorse of ammunition industry ballistic labs, covering interior and exterior ballistics in one system. Two 12-bit ADCs sample two pressure signals (case mouth, mid-case or barrel pressure) simultaneously at 5 or 10 microsecond intervals, storing 400 points per channel and computing peak pressure, time to peak, rise time and area under the curve automatically. The same shot also records muzzle velocity, impact point and time of flight, from which the ballistic coefficient is derived. A built-in firing simulator lets system setup and operator training proceed without live ammunition, and data exports automatically to Excel for the existing quality process.

Supply and export assessment

Evencat supplies the full Oehler Research range with configuration advice and quotations. Note that the manufacturer restricts international export of the system-class models System 83, 84, 85 and 88; supply is assessed case by case against end use and end user, and lead times are longer. Chronographs and sensors such as the Model 35P, Model 36 and Skyscreen III carry no such restriction. We recommend contacting us early in project planning so the configurations that can be supplied are confirmed in time.