Semi-Auto or Full-Auto?

Thursday, June 18th, 2009

If you’re armed with a modern assault rifle, which can fire in semi-auto — one shot per pull of the trigger — or full-auto — like a machine-gun — when, if ever, should you shoot just one shot at a time?

A series of 1968 studies by the US Army concluded that semi-automatic and automatic fire produce different hit ratios at different ranges within a set time period.

Surprisingly, at more than 50m but within comfortable visual range, semi-automatic aimed fire gave the most target hits. The semi-auto mode encourages aimed shooting while, as we have already observed, the muzzle-shuddering characteristics of full-auto fire tend to throw off the aim.

Below 25m, however, full-auto fire produced more hits, reflecting the fact that at close range a single swept burst was likely to include multiple hits.

Beyond comfortable visual range (say above 800m), and excluding professional sniping, full-auto machine-gun fire gave the greatest likelihood of target strike, this creating a generally destructive “beaten zone” (the elliptical pattern on the ground where the bullets strike) in which a target was unlikely to survive unscathed.

Furthermore, between 50 and 300m semi-auto fire was always the quicker in terms of time elapsing from first pull of the trigger to a target hit, proving that at practical combat ranges well-aimed fire is generally the most effective, even if it uses fewer rounds than full-auto fire.

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