GUN CONVERGENCE - How big of an area?

[Jank]

If a fighter with six or eight .50's mounted in the wings had their guns set to converge at say 300 yards, how large of an area would experience strikes?

[Tony Williams]

If they were really all aimed at the same spot, probably around 3 metres. It was more common for them to be spread though, with different pairs of guns converging at different distances.

That assumes no movement on the part of the aircraft while the burst is being fired, of course. In reality, the spread would be greater due to turbulence and the fact that the fighter could not usually hold a precise aim on one spot, but tracked slightly across the target - the RAF called this "aim wander".

Tony Williams: Military gun and ammunition website and discussion forum

[Lt. Z0mBe]

I watched a show on the Hitlory channel about P-51 drivers. They said that had two choices when setting convergence. Basically, all could be toed in to fired through a conical area. The other option was to have all the rounds pass though a circle "the size of a two-bit piece." Pretty big sledge hammer.

It may have been a show about the Tuskeegee airmen come to think about it...



Kenny

[Tony Williams]

Originally Posted by Lt. Z0mBe

The other option was to have all the rounds pass though a circle "the size of a two-bit piece."

Yeah, I've heard about the History Channel...

At 300 yards, you're not going to get all the rounds from one, very carefully aimed, sniper rifle through a two-bit piece. From just ONE .50 MG, firmly locked down on the ground, you'd be lucky to keep them within a yard. From eight? In aircraft wings? When flying?

Tony Williams: Military gun and ammunition website and discussion forum

[lesofprimus]

Gotta agree 100% with Tony...

[Lt. Z0mBe]

Guys, I'm pretty sure it was a metaphor.

The point was it was shotgun (conical) or sledgehammer ("two-bit piece"). That was the pilot's choice of words - "two-bit piece."

Kenny

[Matt308]

Agreed Kenny. A more interesting question is how to properly sight in wing mounted cannon and MGs when the projectiles do not have same ballistic coefficients nor ballistic paths.

You end up with some aircraft using MGs for ranging and cannon for final kill.

Your question has multiple answers dependent upon airframe, weapon system, pilot preference and mission context. Any single answer is dubious in my eyes.

On a side note, I do have 8th AAF tests patterns of B-17 and B-24 gun positions for 10rounds fired at 500yds. The results are varied dependent upon aircraft, turret vs handheld emplacement, and turret manufacturer. The stats also include % of attacks from 8 different compass points taken from ETO. Fascinating really.

[Hop]

Presumably the "two bit piece" was built to the same scale as the "pickle barrel" the US bombers were aiming at

[Twitch]

Factory settings were 300 yards to make a 3 foot square convergence. This was quite easy to do- static boresighting and testing whilst the aircraft was on the ground. Dynamic testing would not have the same results.

Once planes were asssigned to pilots in combat zones they made the choice of where they desired the guns harmonized. Crew chiefs instructed the armorers per the pilots wishes. Some harmonized all guns at a fixed range and some staggered range 2 guns by 2 to vary in convergence.

Most pilots left the guns alone until they got experience under their belts and had an idea of what worked best for them with the tactics they employed.