Burst Selectors: Going the Way of the Dodo?

1435084463

Hognose, over at his blog Weaponsman.com, has written a tidy rundown of the past, present (and probable lack of a) future for burst-limited automatic small arms. A sample, and further discussion, is below, but I encourage my readers to click through and read his article first, then continue on:

A couple of years ago, the Army gave the lousy three-round-burst selector switch that was used on the M16A2 and successors, and the original M4, two in the chest and one in the head. There are still firearms with the bad trigger mechanism kicking around the services, but this decision was the beginning of the end of a gadget that was beloved of ordnance officers and log dogs, but utterly loathed by the guys who actually had occasion to launch those bursts in the direction of an armed enemy.

Burst mode has been experimented with almost as long as automatic firearms have existed; for example, some sources claim the 1890-1900 Italian Cei-Rigotti carbine was so fitted, although the best Cei-Rigotti source on the net, this page at Forgotten Weapons, doesn’t mention it.

Ultimately, this bit of 1960s technology was adopted in the 80s by the US Army and USMC, and had about a 30-year run in service, but it’s on the way out, with many powers opting to arm their men with a conventionally select-fire assault rifle, with safe, semi, and full-auto settings.

Current thinking in the United States and elsewhere in the West is that the value of fully automatic fire for the individual weapon was exaggerated in the immediate post-WWII environment. While it’s true that rifles are fired mostly on semi-automatic, with the fully automatic provision essentially reserved for ambushes and other critical times (which, Hognose notes, “when you do need it, you need it urgently.”), it’s also worth nothing that most of the American experience of the past 30 years has been with weapons sporting 3 round burst only. Considering that 3 round burst has been shown to actually reduce hit probability versus fully automatic (rounds 2 and 3 typically go wide – warning: Link starts a download), and that the burst mechanism used in the M16A2 Rifle and M4 Carbine negatively affects the trigger pull on semiautomatic, it’s not hard to imagine that this re-evaluation of the usefulness of individual automatic fire might be short-lived. It’s certainly possible that the Army’s transition to the new S-1-A fully automatic M4A1 Carbine could be the herald of a renewed emphasis on fully automatic fire from the individual weapon, and indeed the Army’s public literature on the M4A1 reflects this.

Meanwhile, the Soviets, and later Russians, never gave up the fully automatic fire setting, nor did they develop the distaste for burst the way the Americans did. Indeed, both the A545 and AK-12 next-generation Russian rifles feature both fully automatic and two-round burst selector settings:

5.45mm_assault_rifle_A-545_-_Oboronexpo2014part4-17

The A545. Image source: Wikimedia.org

 

1435084463

The AK-12. Image source: world.guns.ru


Nathaniel F

Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. In addition to contributing to The Firearm Blog, he runs 196,800 Revolutions Per Minute, a blog devoted to modern small arms design and theory. He can be reached via email at nathaniel.f@staff.thefirearmblog.com.


Advertisement

  • Major Tom

    Burst fire is a nice idea in theory. Conserve ammunition at medium (100-300 meters) ranges which allowing more rounds on target than conventional semi but not being nearly as wasteful or uncontrollable as auto.

    The problem then becomes a burst fire only weapon is outgunned in CQB, suppressive fire tactics, and when you really need to hose down a lot of (closely packed) guys very quickly range be effed.

    The ideal solution is simply a composite trigger group with a consistent pull on everything. Semi for long range, burst for medium, auto for area targets and close range and all having the same consistent trigger pull needed to keep you working good. The Russians know that value, it’s surprising we don’t.

    • Anonymoose

      I really like the idea of a 4-position selector. It can be done (and it has for over 40 years), but it’s hard to implement on an M16 lower.

      • DW

        Taiwan’s T-65 and T-91 rifles (both AR15 pattern) have 4 position safeties. Triggers still suck on all mode though.

      • Colt offered a 4-position selector option on their “Enhanced” models.

        • Major Tom

          I’ve heard of aftermarket SSBA (Safe, Semi, Burst, Auto) trigger groups with proper 4 position selectors for M-16 family rifles. It’s not just Colt.

          • Anonymoose

            Yeah, you can still buy them for your registered lower. The selector rotates over the little nubs that usually prevent you from moving it more than 180 degrees.

    • DW

      Problem might be in the design of AR trigger. There are triggers that 1. have both burst and auto function 2. that doesn’t make semi-auto crap (crappier? given most mil triggers are bad) 3. can actually be put on safe hammer down. It can be done, just that few have done it for the AR, and it can’t be sold to civvies.

    • Ron

      You really don’t use an Auto in “CQB” although the Marines did for a short period of time train to use Burst for room clearing in Iraq because they found the ability to rapidly deliver COM hits worked better than standard failure drills because of the difficultly in hitting moving heads of wild jihadist who were often on drugs inside buildings. Not to mention 99 percent of time when troops talk about CQB they are actually talking about close quarters marksmanship (Army term) or close shooting (Marine term) as a component of MOUT.
      With the 3rd burst in the M16 FOW you can still unload the 30 rnd mag in approx. 4 seconds compared to the approx. 3 seconds for auto selector.

      • Major Tom

        That’s the thing. Using Burst on an A2 or A4 M16 (or M4) meant more rounds and greater probability of kill in tight quarters when aimed for center mass. Auto does the same thing but is even better. If two groups of equally trained combatants fight in room to room scenarios, the side who can put out more bullets is usually the winner. In CQB scenarios like that, switching to Auto will thump Burst every time. So what if Burst saves you a couple of rounds during a 3 second exchange of fire? It does you no good if the enemy on Auto kills you first. Even if it cost the enemy his entire 20-60 round mag. You can replace ammunition a lot easier, cheaper and faster than it takes to replace casualties.

        That time comparison speaks more volumes about the need to have Auto but with reduced fire rate (like an AK-74M’s 650 rpm) than any advantage for Semi or Burst. You can train troops to control automatic fire to 3-6 rounds even under combat conditions, you can’t train the enemy to fight in accordance with your obsolete rifle doctrine.

        • Ron

          From years of training people (both mil and civ) for and than leading them (military only of course) in combat my observation is you can train people on a square range to consistently shoot controlled bursts. Take those same people off the square range and put them into the stress of a fire fight and you see their trained to burst length increase significantly. It is kind of like when you put someone into a shoot house with simunitions and how often you see them run to slide lock or an empty magazine with a rifle when they were trained to fire a failure drill or a NSR which should not have involved putting 15 or 30 rounds in the target.
          However CQB is a specific battle doctrine normally involving surgical shooting, while what you are referring to is a technique used in close shooting in MOUT. There is a difference and most people seem not to understand they, nor 99 percent of the military don’t do CQB so defining requirements based on CQB when it is not being done does not make sense

  • Anonymoose

    The M16A2 trigger is fundamentally flawed, in that it does not reset if you let off before the burst is over. HK, FN, SIG, and Izhmash rectified this problem, but Colt and Beretta never did. Granted, the Safe-Semi-Full triggers on the M16 tend to be the nicest triggers on military rifles, but with some work it could probably be made to be nice and crisp.

  • Ron

    Although the execution of the burst device on the M16 FOW is flawed, I am actually a fan of burst limiting devices on combat guns. I have seen too many times in fire fights were light and medium machine gunners laying into the trigger significantly longer than they are trained to do.
    You can fire off the entire 30 rd mag of a M16 FOW on burst in around 4 seconds as opposed to the 3 seconds it takes for an M16 FOW on auto

  • USMC03Vet

    I keep reading about “bad triggers” in the m16a2/a4 on the Internet. Worked fine for me.

    • KestrelBike

      Regarding that last bit, are you saying that AAR’s have shown that dudes were hosing with the weapons on burst (as close as they could get to full-auto) causing the weapons to malfunction due to overuse in a short time-frame?

      If so, were they doing this just to put as many rounds downrange as possible, even though it wasn’t tactically smart or effective to do so?

      • Ron

        The feed back from the Battle of Wanat (COP Kahler) was after the heavy weapons were suppressed and or destroyed troops on the ground pressed their M4s and SAWS to the point they were seizing from heavy volume of fire. However since SAWS were failing from the high rate of fire one cannot expect M4 or M4A1s to have done better.

        • USMC03Vet

          Was that the one where someone won the medal of honor? I think that is the one I’m talking about, but yes, troops not following the training regarding fire rates even without using automatics.

          • Ron

            SSgt Ryan Pitts the Platoon FO received the medal of honor for that fight.
            That area had numerous fights that in which US BPs/COPs were almost over run and soldiers involved in the defense of those bases received the medal of honor.

          • Holdfast_II

            I think it was the enemy who attacked in overwhelming numbers, thereby violating USMC doctrine, and which numbers required an unsustainable level of fire to repel.

          • Ron

            Since it was troops from 173d Airborne Bde and not Marines, I don’t think Marine Corps doctrine had anything to do with it. Additionally where in any Marine Corps Doctrine Publications (MCDP 1 WARFIGHTING, MCDP 1-0 MARINE CORPS OPERATIONS, MCDP 1-1 STRATEGY, MCDP 1-2 CAMPAIGNING, MCDP 1-3 TACTICS, MCDP 2 INTELLIGENCE, MCDP 3 EXPEDITIONARY OPERATIONS, MCDP 4 LOGISTICS MCDP 5 PLANNING, MCDP 6
            COMMAND AND CONTROL) do you find anything about rate of fire for small arms?

            What most people refer to as doctrine for the US services is not in fact doctrine, it is normally Tactics, Techniques and Procedure. In the realm of words means things, Doctrine is the “big blue arrows” of how the US military fights while TTP are methods used for units to carry out doctrine.

  • Michael R. Zupcak

    Anyone else hate the “30” instead of text or pictogram by the fire selector? It’s like “How DARE you presume my magazine only holds 30 rounds!”

    …or, the New York and California version: “How DARE you presume my magazine holds anywhere near that much ammunition!”

    • Kelly Jackson

      Deus vult

    • BrandonAKsALot

      I’m just upset they no longer say “АВ” and “ОД”.

  • Lope

    It was just regular Army and Marines who had burst instead of full-auto. Everyone else (foreigners, SOCOM, the Navy) had full-auto. FA is really useful for breaking contact. Everyone can be an automatic rifleman.

  • Lee Attiny

    The military is currently phasing out Colt M4’s with select fire in favor of polymer 80% lower kits with bump fire stocks.

    • Ambassador Vader

      I heard they were also going to be using tac-con triggers with gat wheels to increase fire rates and save lives.

  • Alexandru Ianu

    The main problem with burst as seen in the US is the fact that the mechanism doesn’t reset after one or two rounds and that there was no adopted M-16 trigger mechanism with both burst and full auto. Now, besides the Russians, pretty much all of Europe and Asia is fine with having both burst and full auto on a service rifle. For example, the current Romanian service rifle (Pa md. 86) has a Safe-Auto-Semi-3Burst trigger group, and the new 5.56 AK that’s going to be adopted retains it.

    • forrest1985

      I think having both burst and auto has always made sense to me. Let the shooter pick the setting they want, when they want it etc…

  • zxcvzxcv

    Burst fire is a waste unless you’re going with a mechanism like on the HK G11/AN-94 where the gun fires the entire burst before the shooter feels the recoil. Without that, full auto with a rate reducer to lower the rate of fire to ~450 RPM would be significantly better at increasing hit rate and conserving ammo.

    • randomswede

      I’ve never fired a burst firearm (the AK-5 and AK-4 are both safe-semi-full) but my “simulated” experience agrees with you.
      I’d say 550 RPM is a good balance where it’s faster than rapid fire semi-auto (0.109 splits on a shot timer) but slow enough that shot placement/recoil management is acceptable.

  • Dave

    The “two-round burst” sounds like a hold over from the SPIW concept, but my sense is that it is a “German thing.” At least the first rifles I’d read about that employed a two-rd. burst were German.

  • Joshua

    “Considering that 3 round burst has been shown to actually reduce hit probability versus fully automatic (rounds 2 and 3 typically go wide),”

    Vs full auto burst or full auto sustained suppressive fire? Also why does round 2 and 3 go wide for regular burst but not full auto?

    “and that the burst mechanism used in the M16A2 Rifle and M4 Carbine negatively affects the trigger pull on semiautomatic,”

    How does it negatively affect trigger on semi?

    Thanks in advance.

    • Here’s a video showing how the burst mechanism of an M16A2/A4/M4 works. You’ll want to watch it first:

      So, the burst ratchet in the fire control group changes the trigger pull on semiautomatic. One of the big problems is that it has “burst memory”, meaning if you let off the trigger before the burst was finished, the next time you pulled the trigger you would get the remainder of the last burst.

      Worse, if you did this and then switched to semi, you would have a different trigger pull than normal. I believe this has to do with the ratchet on the burst wheel thingie.

      My understanding about the hit probability is that the second and third rounds of the burst tend to fly off target, before the shooter can pull the gun back on target for subsequent rounds. In fact, the Army has known this since 1986 (link starts a download):

      “During the limited research we have conducted in automatic fire experimenting with burst size, various holding positions, etc.–we are finding that three-round bursts may not be the optimum burst size. In the majority of bipod-supported automatic fire holding positions, firing up to five and ten round bursts, the third round will many times find the limit of the group size, with subsequent rounds moving back in toward and around the initial aiming point (see Figure 12). Therefore, an increased hit probability may occur with a five or six round burst on target, as opposed to two three round bursts. Also, some targets do not stay, around for a second burst, and sometimes the firer is not around for a second burst.”

      • ostiariusalpha

        So, that begs the question of whether a resetting 6-round burst would be worth testing against full auto.

        • Doesn’t seem likely, TBH.

        • Colt played with a non-resetting 6-rd burst cam back in the 1960s. Dave Lutz mentioned that he had known about it, he would have considered using it instead of the 3rd burst cam in the M16A1E1.

    • Ron

      That either quotes from or paraphrases the Army study done when the Marine Corps was pushing for fielding of the A2. The bottom line was the Army never liked the idea of the burst limiting device or the fact the Marine Corps lead the charge for the upgrade from the M16A1 to the A2.

  • BrandonAKsALot

    The Tantal/Beryl 3-round burst is pretty cool and well thought out. It increases trigger weight some by adding in an extra spring, but it’s relatively simple.

  • Fegelein

    So it looks like the easterners were right all along — just teach the guys to mind their fire.