A friend has an FN model D machine gun. I think the selectable rates of fire is a neat feature. I can't say exactly what that feature's tactical application might be; perhaps slower rate for more precision strings at longer ranges, and the fast rate for the real "oh shit" circumstance? I assume the military opted not to have that feature on contemporary guns for a reason; anyone know what it is? Why would it have been desired then, but not now? I know the timing is adjustable on the M2, but it's not performed at the flick of a switch. It seems the M134 is selectable as well; is that performed on the fly, or is it something that's chosen during setup, and not modified easily?

The rate of fire is selectable on the 1918A2 BAR.

Of which the Model D is a descendant, I believe.

The utility of automatic fire is better understood, and the weapons that utilize it need less flexibility. I'm guessing..

Mechanical simplicity is also a factor, but the major thing is actually that automatic fire is a more focused role than previous decades of war fighting.

The M134 is "selectable" between 3000/6000, correct? One or two triggers... Which is just "No" and "Fuck No."

By machineguns, do you mean crew served, or anything once capable of full auto?

I suspect the reason is that the employment of modern machine guns has benefitted substantially from improved training and tactics. Nowadays, machine gunners are trained to regulate their rate of fire with controlled bursts, ideally timed with another gunner who is doing the same. Cyclic rate becomes less important when one is thoroughly trained in the operation of their weapon platform.

The M134 is a different animal, and generally isn't applied in situations where a light/medium machine gun would be utilized.

quote:

By machineguns, do you mean crew served, or anything once capable of full auto?

I suppose I mean a weapon capable of fully automatic fire, cambered in an intermediate or full caliber, that is intended to be fired primarily from a bipod, tripod, or other support fixture; fed from either a belt or magazine. Requiring a "gun team" is not a prerequisite for consideration, but I am not considering a full-auto carbine.

quote:

Originally posted by Ironworker:
The rate of fire is selectable on the 1918A2 BAR.

Roy Dunlap wrote in 'Ordnance Went Up Front' that the rate reducer was the main cause of repair calls in the PTO. Older models without it still in service were prized.

Maybe variable ROF just made a bad first impression. It's likely reasonable to hypothesize that the same mechanisms, if given a chance at revision, and made with modern alloys and manufacturing techniques, would be plenty reliable. A safe, semi, burst (without "memory"), auto trigger mechanism is pretty complex, and there's plenty of them that have proven track records. But, being open bolt, I understand that the BAR modified it's rate of fire by affecting a change in the buffer mechanism, thus delaying the bolt assembly's forward return. If I am right in saying that, would it be right to say that it was this buffer assembly that was the failure point?

If the rate of fire modifier in a closed bolt weapon, regulated by the trigger mechanism, was proven reliable, what might be arguments for or against it's use? Why did they deem variance worthwhile then; why don't they now? I know folks have mentioned changes in weapon theory being the cause, but what exactly is the theory? Surely they knew then that firing shorter bursts saved ammo and increased accuracy; it doesn't take a genius to figure that out.

As an aside OP, the “adjustable” timing on the M2 actually is designed to ensure the round doesn’t go off before the chamber is closed and blows pieces of brass into a shooters legs and feet.

The timing is set by a nut inside the receiver and usually locked down with a folding/bendable tab. We had a unit that thought they could speed up the gun to shoot cyclic and found out the hard way. A SN caught brass shrapnel all in the legs. After talking to everyone the BM2 said he had read the TM on the gun and thought he could make it run faster. Which was true to some part, but he sped the gun up beyond being safe. Don’t know if he lost a stripe or not, but my armory had to send the gun to Crane to have them set it back correctly as even at the Armory level we weren’t allowed to adjust the timing nut.

Maybe the Army does things differently. I dunno.

/drift

quote:

Originally posted by KSGM:
...the fast rate for the real "oh shit" circumstance?

Possibly because the added mechanics and headaches that come with it weren't worth it when the average end user saw all its non training use as "oh shit" circumstances and it was the default setting?

Hahaha. You might be on to something there.

The "adjustable rate" on the M-249 & M-240 is at the gas block. IIRC, it was designed so when the gun was being shot in the 750-800RPM range and the weapon was filling up with carbon and gunk, it slows down the cyclic rate, you can open that puppy up a little bit, and carry on at a 750-800 RPM.

Or you can just have some fun out of the gate, and open her up all the way, and let-it-rip-taterchip! 1000RPM is extremely fun when Uncle Sam is buying the ammo! Hell, anything is extremely fun when Uncle Sam is buying the ammo!!!!

I think the current M249 lacks any adjustability at the block.

The Germans had two MG for WW2.
Going in they had the Machinen Gewehr of 1934. It was a beautiful piece of machine work. Lots of very fine, precise work. This means it was a very labor intensive and expensive weapon to build. Almost every machine cut required close tolerances, quality control/testing to maintain that quality. Let’s assume each model ‘34 had a hundred different parts. Each part has 5 (wood butt stock) to 20 cuts. Some have many more. Let’s assume a conservative average of 15 cuts per part. 1500 cuts per gun. Some loss with rejected parts.
Additional feature - this MG had a special, long (tall) trigger. Finger high - it shot semi-auto. Finger low - it shot full auto. This was another complexity in an already expensive weapon. While I have yet to examine the mechanics, I understand it to be an intricate mechanism.

In a nutshell - this was an expensive weapon to build. More so due to the select fire design. The cost, complexity and time required to manufacture the weapon motivated a move to something simpler, cheaper and faster to produce.

The result was the MG42. It achieved all of those things without a select fire option. An additional (unintended?) result was an increased rate of fire. For reference, the Browning machine gun rate of fire was/is about 400-600 rounds per minute(rpm). The original/early production MG34 fired at 900 rpm and the MG42 fired at 1200 rpm.

After that bit of history, shooting a lot with a machine gun is easy. Shooting a little is more of a challenge. As I understand it, in Viet Nam there were times that a single shot from the M2HB was desired. With practice some of our guys could do it. It involved very careful control of the trigger. More commonly the recommendation was to fire in short bursts.

Can select fire machine guns be designed and built? Sure. The M-16 and its many variations are prime examples. For other, larger, maybe crew served weapons? The cost, complexity and effect on reliability aren’t justified. Releasing the finger works well enough.

I think you misunderstood, Chris42... The OP isn't talking about machine guns that feature "select fire" capability (able to switch between semiauto/single shots and full auto).

He's talking about machineguns with an adjustable rate of full auto fire.

For example, the original design of the MG34 had a selector button on the grip assembly, just behind the trigger, that actuated an internal clockwork mechanism which could be used to make the MG34 fire at either 600 RPM or 1000 RPM in full auto. (In addition to the dual trigger mechanism you mentioned that allowed you to shoot either semi- or full-auto.)

That overly complicated rate of fire selector was abandoned very early on in production, and nearly all MG34s that were produced had a single fixed rate of full auto fire of ~900ish RPM.

That's the type of thing KGSM is talking about, adjusting the cyclic rate of full auto fire, not simply selecting between single vs. full auto.

If I recall my ancient teachings on the M60, we were taught burst control which more less set the rate of fire.

quote:

After that bit of history, shooting a lot with a machine gun is easy. Shooting a little is more of a challenge. As I understand it, in Viet Nam there were times that a single shot from the M2HB was desired. With practice some of our guys could do it. It involved very careful control of the trigger. More commonly the recommendation was to fire in short bursts.

Chris, the M2 has a single shot option-always has. It’s a metal band around the buffer that sticks out of the cylinder between the handles. (Bolt latch lock) The Gunner can twist that band which unlocks the bolt latch (center button looks like a tombstone) which causes the gun to operate in single shot. If the bolt latch lock is twisted counter clockwise it locks down the bolt latch and the gun runs in auto until the Gunner releases the trigger.

Rogue - you are correct - I DID mis-read the OP. Adjustable was a detail I saw as semi or full auto. Thank you for the correction.
Mike in NC - Now that is a detail I never know about. Something we didn’t cover at Great Lakes in the great, green cube. What I wonder there is if John Browning made that part of his design or if that was an added detail. Was it a feature of his .30 cal. guns?

Sorry for the thread drift -

Chris, I’ve only shot a m1919 once and the backplate is different than the M2 even tho it’s sized up from the m1919. The 1919 has an actual trigger under the recoil buffer and doesn’t use a trigger mechanism like the m2. But I’m going off shooting it 20 years ago. A friend has two of them he made from kits and they shoot 308 vs 30-06.

/drift

The FN D is such an awesome MG. A good friend has one. I love shooting it.