If you haven't read JM's post on small arms suppressive fire here: https://mountainguerrilla.wordpress.com/2012/11/09/suppressive-fire-for-the-irregular-war-fighter/ go do so now.
Everybody on the same page? Good.
Suppressive fire is about making the enemy unable to maneuver against you (so you can leave such as in a break contact scenario or maneuver your own force against them in an attack). Suppressive fire means the enemy is fixated on the obvious source of fire and can not effectively maneuver against it for some period of time (nothing lasts forever, no matter what the De Beers advertisement says). Get that? There is no "rounds per minute math" here in the very bottom level definition of suppressive fire. The combat math is useful to figure out how long you should be able to suppress for planning purposes (which lets you plan how quickly you need to get your assault position in place), but it is not a measure for success.
If you have four men in a fire team, all huddled in a mortar crater, and they are all afraid to put their head above the rim because a lone rifleman pings one off their helmet before they get their eyes on the horizon, THAT is effective suppressive fire.
A lone rifleman won't keep the fire team pinned down for long, the Team Leader will issue orders to two of his men to dash in opposite directions at the same time while the other two try to "shoot likely positions of the enemy" to break out of a bad situation. If our pinned down fire team is able to do so, then the suppressive fire did not last very long. Suppressive fire must be lethal to be effective. If you are pulling the trigger and not killing or wounding someone then they are planning to exploit your failure to kill them.
Remember the 77 Maxim's of Maximally Effective Mercenaries: That which does not kill you hath made a tactical error.
Suppressive fire is about the effect on the enemy, not number of rounds fired. I cannot state that enough. If I were instructing a class of new Infantry Officers I would have stomped my foot while I said that. I can't emphasize that enough. You don't need a machinegun to achieve suppressive fire. It is nice to have, but it is not necessary.
What is necessary?
First is Accuracy. A near miss is still a miss. Enough people have
now experienced bullets zinging very close to them that they are not
afraid of improperly aimed fire. You have to hit where you are aiming
to be effective at suppressing the enemy. Calling a miss "suppression"
is just an excuse for bad marksmanship (and remember, Marksmanship Matters a great deal at the tactical level).
How do you choose the weapon systems for your "Fire" element of Fire and Maneuver? Look at the target, and decide what you need to be effective against it.
The second necessary element is Force. Will your bullets be able to achieve good destruction of the target?
reinforced concrete bunker will soak up a lot of 7.62 before giving
way. More than an Infantryman can carry. It will soak up a lot less 50
cal. It will just shrug off 5.56.
A brick wall will get punched through by a 50 cal, and get tore up very quickly by 7.62, but 5.56 won't do much.
A wooden wall (barring some thick log cabin monstrosity) is no obstacle to 7.62 and 5.56 will chew through it nicely (for a few walls anyways).
22 long rifle has plenty of energy and accuracy for quick fleeting
targets under 50 yards for headshots. Do not discount some crazy guy
with a bunch of 25 round magazines for a 10/22 as being able to keep a
bunch of men with superior arms pinned down. Accuracy is the first part
of the lethality equation (accuracy, penetration, deformation), and the first part about providing effective
If your suppressive fire efforts are part of
a "reaction" drill, then all those "force" planning considerations go out the
window and you return fire with whatever you have in an attempt to gain
fire superiority. React to contact drills are all worth their time in
gold to rehearse.
The third consideration is Volume of fire. After your bullets
arrive at the target with enough force to be lethal, or penetrate
whatever barrier you want to break down you need to be hitting the target with the appropriate frequency to keep the enemy from moving. Your fire must be quick enough
that the enemy is stuck in the O portions of their OODA loop. Whether
you do that with five AR-10s at 500 meters or 20 guys with 30-30 rifles
at 200 meters is all METT-TC dependent (but make a choice based on those
factors). The timing is different for different weapon systems, if you have a bolt action rifle, you cannot fire a second shot fast enough to make up for a near miss, with an AR you can. As JM wrote, this frequency really depends on range, so use enough volume to achieve suppression, but no more.
There it is, accuracy, force, volume. Now that you know you need to provide accurate fire, that is doing the desired damage to the enemy, you need enough volume to achieve tactical superiority. This is where machine guns are nice, but not necessary. The more accurate your fire, the less volume you will need, which means you can use fewer rounds to achieve suppression for a longer time..
How does accuracy, force, and volume of fire interact with tactics?
In the offense, How do you make the enemy fight in two directions? You have a base of fire (such as a Support By Fire position or an Attack By Fire position) This lays DIRECT FIRE on the enemy. This makes the enemy seek COVER if possible, CONCEALMENT if not, to keep from being killed. If you are "Supporting by fire" then your assault element will maneuver to the enemies flank, and begin their assault. This is where the support by fire line has to turn off bullets ahead of the advancing assault. This always involves some sort of front line trace and communication backup. If it doesn't you will end up with fratricide.
If however you are in an Attack By Fire position, the other direction can come from indirect or air assets. Your direct fire makes the enemy duck behind something, then mortars or artillery explodes overhead. The enemy dies without any extra maneuver force moving across the enemy position. This is a very useful tactic if you have the assets to do so. If you don't you can set up two Attack By Fire positions, using terrain, to attack the enemy from two directions and achieve the same "destruction" without an active maneuver force. Think of this as an L shaped ambush without an assault prior to exfiltration.
In the defense, you engage the enemy in prepared
engagement areas, using the principle of Attack by Fire or Support by
Fire in an "aggressive defense" principle. The Army Qualification for
small arms is based on an "aggressive defense" scenario. However there
is no difference between "aggressive defense" and "suppressive fire" in
terms of how you employ the weapon system.
If someone ever asks you "What do you do in this situation?" responding with, "Well it is METT-TC dependent" makes you sound like an unprepared ROTC Cadet. Ask them where they want to conduct an operation, pull out the map or walk the terrain and go through a hasty planning scenario. Talk through the Mission, Equipment, Time, Troops, Terrain, and Civil considerations, explain your reasoning and logic for each step. That is how good leaders are developed. If you aren't training one or two people to replace you at all times you are failing your organization. If you don't have a map, or someone is just being a smartass (remember, all tactics can be defeated, there is no Buddha Palm Death Punch) then don't waste your time.
JM listed Rommel's "Attacks" as a good source of learning for small unit tactics involving fire and maneuver. I've read it, and think that someone should start of with "Battle Leadership" by Adolph Von Schell. Between the two I think Von Schnell was the better teacher, but that truly is just my opinion after reading Attacks and Battle Leadership. Everyone should read Rommel (Just like everyone should read Sun Tzu and Clausewitz) but I think if you read Von Schell first it will make Rommel easier to understand.