It seems impossible that they could hit anything, did they?
First, let’s get it out of the way : “I done got me 157 dead gooks killed. Plus 50 water buffalo, too ! Them’s all confirmed !”
Now, for more serious. First of all, Hueys weren’t all that fast : Wikipedia lists a cruise speed of 100 knots which is much slower than, say, the diving speed of a WW2 ground attack aircraft. Which, granted, were woefully inaccurate. But over time, statistically, given a high rate of fire, y’know, sometimes a barn got hit or something :).
Also, IANADG but seems to me the point wasn’t to fire while the choppers were zooming about (as happy funtimes as that might have been) but to provide area suppression at the landing zone, to cover the troops, not to mention the chopper itself, while they were jumping out and extremely vulnerable. Possibly also some strafing fire on a given area as the chopper drew lazy circles around the target.
I read a story written by a pilot of a Cobra attack helicopter in Vietnam. He began his tour as a co-pilot and occupied the front seat, which controlled the minigun. That gun fires up to 6000 rounds per minute. That’s fast.
He described following a buzzard one day, and being challenged by the pilot to shoot it down. He unloaded all 6000 rounds (the ammo load) on that buzzard as it lazily moved from side to side to avoid the fire. Needless to say, he had 6000 misses.
So, I’d say hitting a moving target from a moving vehicle is much harder than it looks.
It’s called suppressing fire and is designed to keep the enemy’s heads down while the chopper is landing and taking off. While a minigun has far more firepower, it’s used for the same purpose (or was, in the pre-computer controlled era).
It’s not necessary to hit your target – throwing ammo as covering fire will keep the enemy’s heads down, even if you don’t hit anyone.
I am a graduate of the Fort Benning Infantry School, I’m familiar with suppressive fire. It seems that after even a few insertions/extractions the Bad Guys would figure out that you’re pretty safe from the door gunners and they could just keep their heads down and blow the helicopters out of the sky.
Was this just a way to keep the Huey crews from feeling helpless?
Lawrence Colburn was pretty effective in a certain way.
It’s hard not to keep your head down when you can hear a bullet fly past your head.
Just to not besmirch anyone’s actions, I’m not asking about bravery from either side. I’m questioning the effectiveness of the door gunner vs. the guy in the jungle shooting back at him.
First off, there is no way he had 6000 rounds. Ammunition is heavy and bulky. While the rate of fire is 6000 rounds out of the M61 Vulcan cannon the typical loadout is much less than that, good for a few bursts only. Also, modern targeting equipment makes hitting a moving target much easier than it used to be, evidenced by the Apache gun camera videos that have made the rounds over the last decade.
As for helicopter gunners, suppressive fire has an effect far out of proportion to the volume of fire, simply because nobody wants to be the guy to catch a random bullet because they’re too stupid to keep their head down in case someone is actually aiming. That said, there were gunners on the ground that could take down a jet at altitude using nothing but their eyeballs, so it’s not implausible to believe that a guy on a fairly stable platform like a Huey could walk some rounds onto an enemy position, especially if he’s loaded with tracers.
With what ? AK fire ? RPGs weren’t exactly as ubiquitous as they are now. Those the NVA had were short-ranged, unguided and inaccurate. Not sure whether the Viet-Cong had any such heavy equipment at all. And besides, when an angry man is sweeping a large belt-fed machine gun in the vicinity it is considered bad luck to bring attention to one’s location :p.
I mean, either they’re suppressed or they’re not. If they feel safe enough to pop out of cover and fire back, by definition they’re not suppressed.
I never had any complaints about door gunners on a slick I was in, exiting, or boarding. Especially if the slick was taking me and my guys back to the FB.
If I’m getting off a bird in a hot LZ I would much prefer some covering fire. Whether or not it actually hits anything. Just keep them busy till I can get to cover.
Being a gunner on a UH-1C gunship, we were very effective. Being in the open door
you could see and hear what was going on, we were very low and 90 or so mph.
We shot what was known as a free gun ( attached to overhead with bungee) it was
a M60 machine gun that had become very modified. We caused a lot of problems
on the ground, and helped a lot of troops with EFFECTIVE door gun fire. The
ineffective didn’t make it.
Suddenly, you seem to be the only person to have been there/done that in this thread.
I should thank you for saving many asses.
So I will. 
I was a Marine in Vietnam in 1969. From personal experience I have to say it was very effective in that it suppressed fire.
The OP’s question, it seems to me, was concerned more with how ACCURATE the fire was rather how EFFECTIVE it was. He was also only asking about the M-60 door gunners, not the mini-gun. I have to believe that accuracy from a moving platform with a gun that can move in any direction is limited. But they put out a lot of rounds that could hit in a relatively small area. And as mentioned above, it’s hard not to believe that they are aimed at you.
So the answer is:
How EFFECTIVE were they? Real effective.
How ACCURATE were they? Eh, probably not so much.
I was a Huey pilot for five years and we always cruised at 90 knots. Fortunately no one ever shot at me and I never shot at anyone but during gunnery practice. our door gunners could hit things pretty well. I will however defer to Carl Peters on this.
I have to make a book recommendation here - About Huey pilots in VN.
It’s an amazing read. From training, to some absolutely crazy stuff they did.
About the Cobra ammo issues above.
Early Army Ah-1Gs 1967-7? had 2 guns in nose turret, 1 mini and 1 40mm or
2 miniguns the unit could select what they needed. The mini gun ammo box held
4000 rds. of 7.62, per gun. The 20mm turret was later in the Cobras life.
More Door Gunner info we used Duplex ammo in our M60s for a long time, these
had 2 bullets in one case. Now you went from 550 rpm you doubled your output
they had green tips.
The same can be said for supressive fire by ground troops. It’s done so that other troops can advance while the hail of fire keeps enemy heads down. It’s not meant to be accurate in terms of kills, but if directed toward known enemy positions, it’s very effective.