Reproducibility (With IMI M193)

**Molon** · 05-01-16, 12:03

Reproducibility

(A Demonstration With IMI M193)

The hallmark of a sound test methodology is being able to repeat a test and arrive at the same conclusion. As a demonstration of this, I conducted two accuracy evaluations of the most accurate lot of IMI M193 that I've come across, from my bench-rest set-up using a semi-automatic AR-15.

I conducted an accuracy (technically, precision) evaluation of the IMI M193 ammunition following my usual protocol. This accuracy evaluation used statistically significant shot-group sizes and every single shot in a fired group was included in the measurements. There was absolutely no use of any group reduction techniques (e.g. fliers, target movement, butterfly Shots).

The shooting set-up will be described in detail below. As many of the significant variables as was practicable were controlled for. Also, a control group was fired from the test-rifle used in the evaluation using match-grade, hand-loaded ammunition; in order to demonstrate the capability of the barrel. Pictures of shot-groups are posted for documentation.

All shooting was conducted from a concrete bench-rest at a distance of 100 yards (confirmed with a laser rangefinder.) The barrel used in the evaluation was free-floated. The free-float handguards of the rifle rested in a Sinclair Windage Benchrest (with the aide of a forend bench-rest adapter), while the stock of the rifle rested in a Protektor bunny-ear rear bag. Sighting was accomplished via a Leupold VARI-X III set at 25X magnification and adjusted to be parallax-free at 100 yards. A mirage shade was attached to the objective-bell of the scope. Wind conditions on the shooting range were continuously monitored using a Wind Probe. The set-up was very similar to that pictured below.

The Wind Probe.

The test vehicle for this evaluation was one of my semi-automatic precision AR-15s with a 20” stainless-steel Lothar Walther barrel. The barrel has a 223 Wylde chamber with a 1:8” twist.

Prior to firing the IMI M193 ammunition, I fired a 10-shot control group using a hand-load topped with the Sierra 55 grain BlitzKing. That group had an extreme spread of 0.83”.

Four 10-shot groups of the IMI M193 ammunition were fired in a row with the resulting extreme spreads:

2.73”
1.76”
1.74”
2.03”

for a 10-shot group average extreme spread of 2.07”. The four 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 40-shot composite group. The mean radius for the 40-shot composite group was 0.62”.

Next, I repeated the test just as described above. These four 10-shot groups fired in a row produced extreme spreads of:

2.64”
1.25”
2.43”
2.00”

for a 10-shot group average extreme spread of 2.08”. These four 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 40-shot composite group. The mean radius for this 40-shot composite group was 0.66”.

I over-layed all eight of the 10-shot groups on each other using RSI Shooting Lab to form an 80-shot composite group. The 80-shot composite group had a mean radius of 0.64”.

The 80-shot composite group . . .

The smallest 10-shot group . . .

…..