Can a Slidefire Effectively Duplicate Full-Auto?

The Slidefire (and other similar bump-fire stocks) is basically a toy when used form the shoulder. A genuinely fun toy, to be sure, but still a toy. However, I have reason to suspect that when used on a rifle with a bipod and large ammunition capacity it might actually do a good job of duplicating a true light machine gun without the cost and NFA paperwork.

(For folks who are not familiar with the concept, the stock allows the action to freely reciprocate in the stock. By holding one’s trigger finger in a set position and pulling the action forward, the gun fires and the recoil energy pushes it backwards enough to reset the trigger. By applying a constant forward pressure on the gun, a pretty steady rate of fire at 500-600 rpm can be achieved with a gun that remains unquestionably semi-automatic by law.)

As a first step in testing that hypothesis, I took a Russian semiauto RPK with a Slidefire stock to this month’s 2-Gun Action Challenge Match. The goal was to see if it showed enough promise to be worth further practice and experimentation…

…and the answer is that it definitely is. My match score was terrible, and the gun had several problems (mostly due to unpracticed handling of the Slidefire), but the potential was apparent.

One interesting thing I took away from the match was some refreshed perspective on the extra stress competition puts on a person’s skills. I am not a top-level competitor at the 2-Gun match, but I have enough practice and experience that I don’t need to devote a lot of my conscious effort to actually manipulating my guns. I can focus on things like sight picture and target acquisition and movement and such, and the basic mechanical operation of the guns takes care of itself. Not so much with the Slidefire. The extra concentration required to operate the bumpfire stock (things like how much forward pressure to apply to the gun and keeping my trigger finger in the proper position for bumpfiring) took a lot more of my attention than a normal firearm. As a result, I found myself making rookie mistakes like failing to use both front and rear sights.

I am anticipating that more practice can mitigate this issue, just as it does for typical guns. As I say in the video, I have been toying with the idea of buying a transferrable LMG for a while, because I would like to practice using one as an LMG (using a light machine gun is a different skillset than a rifle, just as effective use of a submachine gun involves a much different skillset than rifle or pistol shooting). The plan had been to find a Type 99 Nambu, for which I already have a 7.62x39mm conversion setup to allow affordable full-auto shooting. But if I can get 90%+ of the same thing for a tenth of the price by using a Slidefire RPK, that would be a much more feasible option.

43 Comments

  1. Whatever that guy was firing, it sounded fun!

    On another (unrelated) note, I’ve found something that might be interesting for you guys. Its a video game/app called “World of guns” and as far as I know, it’s free to download, though you have to pay for the extra guns that are released every so often. Tons of cutaway and Xray options too, as well as being able to fire them. It’s pretty neat seeing the inside of an AK during firing!
    http://www.all4shooters.com/en/home/generic-news/World-Of-Guns-Gun-Disassembly-educational-videogame/

    Might want to check it out. I figured you might be interested, especially when I saw they’re doing older weapons too! (Borchardt pistol, broomhandle mauser, or colt pocket hammer anyone?)

    http://noble-empire.com/apps.php?app=gun&page=models

    Right now, their “lifetime” package is about £13, which includes all the current weapons and grants free access to any new releases as they come out.

  2. I am looking forward to more videos of this after you have mastered the technique involved in shooting the bump-fire RPK. Hell, it was fun watching it in action as is! I would love to do something similar here with a regular AK, but our Rod and Gun club does not allow bump fire stocks or even legally owned full auto guns to be fired on its range- and this is true of most ranges in Pennsylvania from my conversations with other PA gun owners. It sucks, but it sure beats living in NJ, Maryland, New York and the other communist states, lol. For this reason I have been considering moving to Kentucky, where such things are more acceptable. Don’t think I could take the hot weather in Arizona though. Keep it up Ian! Your videos are fun to watch.

  3. Do you think it would be feasible to put a moveable grip on the underside of the stock, so you can hold the gun “correctly”?

  4. “gun that remains unquestionably semi-automatic by law”
    I assume that you are referring to NFA 1934 which states that:
    “The term “machine gun” means any weapon which shoots, or is designed to shoot, automatically or semiautomatically, more than one shot, without manual reloading, by a single function of the trigger”
    If so (from law point of view) machine gun with trigger mechanism replaced with part causing firing as fast as machine gun is reloaded and as long as belt is not depleted is NOT machine gun?

    • The bump fire stocks such as the slide fire brand used here do not replace the trigger mechanism at all. Your trigger finger bumps into the trigger one time for each shot that is fired. The gun recoils and slides backward enough to reset the trigger between each shot. You slide it back forward manually for each shot (adding a spring to the stock makes it a machine gun according to the ATF).

  5. Unfortunately, the only way to make a real comparison would be to put a true SMG up against a semi-auto rifle with a bumpfire stock. Also, under stress the SMG will always function as an SMG, the bumpfire requires the gun to be operated “just so” and is sure to occasionally fail to function in a stressful situation.

      • If the question was “Is a bumpfire stock and a semi-auto rifle cheaper than an SMG” the answer is obviously “yes” … but the question is, “Can a Slidefire Effectively Duplicate Full-Auto?” … the answer to that can only be determined if you put one against the other over the same course of fire.

  6. If your rifle’s handguard was an integral part of the grip / buttstock assembly, you would have had a much better time, as you wouldn’t have been able to apply too much pressure on the slidefire spring system.

  7. The Slide Fire will never duplicate a real select fire weapon. But that’s not the point it is to simulate full auto fire, which is FUN!. For effectiveness aimed semi auto fire will always be better for your average person.
    The best Slide fire combo I have seen was a heavy barreled AR15 which also had a Tac-Con trigger fitted. That seemed to work very reliably and I would have guessed produced around 500rpm cycle rate.
    Just a suggestion Ian might be worth investigating combining your RPK with a different trigger combo?

  8. Thanks for the great video! My only thought is that in 2-Gun, success is measured by achieving HITS. For an LMG, in some instances, success is measured by achieving SUPPRESSION.

    There were a few occasions where you fired a burst and we could see impacts all around the target. The bystanders were calling out fire corrections – “you still didn’t get it”. However, it seems that target would have been suppressed. That allows team mates (not part of 2-gun) to maneuver.

    Obviously killed is suppressed forever, so its good to shoot for that, no pun intended.

      • Too bad we don’t have any crazy fantasy or table-top-role-playing-game monsters to kill. Sadly, killing a fire-breathing dragon here will not yield you a fat wallet too stuffed for us to sit upon!

      • You mean you don’t have an Oehler screen or Weibel radar array???

        Tyvek billboards behind the silhouettes? and an intern to score them all?

  9. Bump fire stocks are fun, but I doubt they’ll be practical. After all, how would you hold it steady if a bunch of fanatic cultists charged your position? Then again, the Slide Fire is much better than the Sputter Gun which had no trigger at all…

  10. What’s the difference between running a SMG vs a carbine? Off the top I’m thinking shorter range, maybe fewer single shots with the SMG?

    • It depends on the SMG. H&Ks like the MP-5 are basically semi-auto pistol-caliber carbines that happen to have a selector switch. They fire from a closed bolt for all shooting, so they’re largely identical to an M1 or M2 Carbine in terms of handling. The Carbine, however, will always outrange them unless you’re using the uncommon .223 HK53 version. (Which has cookoff problems on full-auto.)

      Thompsons of the 1921 and 1928 versions, plus the M1, are handled the same way. The M1A1, however, is an open-bolt, fixed-firing pin, advanced-primer ignition (“slamfire”) weapon, and as such requires a bit more practice to hit with due to that heavy bolt lurching forward with every trigger squeeze. At least it has a single-shot setting. The same is true for the Sten family, as well as the Uzi, Vz24/25/etc. clan, and similar early third generation SMGs. Even the Ingram (MAC) family have single-shot settings, although the combination of a very light gun and extremely heavy bolt makes hitting anything much beyond 25 meters more of a conjuring trick than anything else, even on single-shot.

      The German MP38/40 and U.S. M3 “Grease Gun” are a bit of a special case. They do not have a semi-auto setting, but their RoF on auto is so low (about 450 R/M), that you can “tap off” single shots by “tapping” the trigger momentarily. However, being open-bolt slamfire designs like the M1A1 Thompson, you have to deal with that “lurch” at the beginning of every firing cycle. Similar SMGS, such as various copies of the M3, are handled the same way.

      As for range, most SMGs have an effective range of about 100 meters on full auto, because that’s about as far as you can successfully hit with them on full-auto with their fairly basic iron sights, and their pistol-caliber rounds fall off drastically in retained energy much beyond 150 meters anyway. The .30 Carbine round’s retained energy at 250 meters is about that of a 9 x 19mm or .45 ACP at the muzzle, to give you some idea of the difference. Also, its adjustable rear sight (out to 300 yards) certainly helps.

      On single-shot (those that have it) it depends on a combination of the sights and your own abilities. In my miss-spent youth, I won a few bets with a 1928 Thompson on semi-auto at 200 meters on a range, mainly due to that beautiful Lyman rear sight. Not to mention scaring the (bleep) out of the woodchucks that infested our range at up to 250. (230-grain bullet kicks up spray of dirt next to woodchuck smugly washing his face at you 200 meters downrange. Woodchuck departs down his hole leaving small yellow puddle behind, etc.)

      No, I don’t like the furry little miscreant known as Marmota monax. He really should have stayed out of my lettuce patch when I was a kid.

      And don’t get me started on Procyon lotor…

      cheers

      eon

      • Thanks for answering. I suppose also with the role an MP-5 would play, hostage rescue CQB etc, the drills and tactics are somewhat different?

        • Exactly. The weapon and procedures used will always depend on the mission, plus of course what’s available.

          As a side note, twenty-seven years ago, the Columbus, OH PD SWAT team (about 20+ miles from me) went from the M1 Carbine to the trendy MP-5 in 9 x 19mm. Thirteen years ago, they went to the milspec M4 in 5.56mm.

          Other than the purely PR problems, the main thing they noticed was that the selective-fire weapons encouraged “spray-and-pray” tactics rather than the precise shooting the “old-fashioned” semi-auto only carbine required. Not all that satisfactory in a hostage situation.

          They were also a bit put out to learn that their vests, which were supposedly proof against .357 Magnum at 10 meters without the trauma plate, wouldn’t stop the .30 USC 110-gr FMJ at 50 meters even with the trauma plate.

          (Something I’d learned in early evaluation work on vests and MP-5s, etc., in the late 1970s.)

          Except for situations where potential over-penetration has to be kept to the absolute minimum, a .30 USC-caliber weapon is probably more useful overall than a 9 x 19mm longarm. And in police as opposed to military use, it might even be a better choice that 5.56 x 45mm. (Even the penetration issue might be managed by careful bullet selection, i.e. JHP or some sort of prefragmented projectile.)

          I might add that the MP-5 would be highly interesting in .30 USC. Especially if fitted with a three-shot burst control and no full-auto setting, like the 10mm Auto version once used by the FBI HRT.

          cheers

          eon

          • Love the good ole’ M1 Carbine.

            After a recent drive-by shooting which took place, ohhhh….100 yards from my bed, I’ve broken out my Carbine, loaded up a reliable 30 round magazine with Speer Gold Dots, and have it hanging from a coat hook in my bedroom.

            I hate my town.

      • Effective range highly depends on SMG in question. Here are Yugoslavian tests of various SMGs:

        5 and 10 rounds burst used at 25 and 50m, 5 rounds burst at longer ranges. Standing shooting position. Target was “chest” target.

        Overall P/H worst to best:
        Sten, MP-40, Thompson (M1A1), Beretta, PPSh-41, M56.

        25m – all equal

        50m:
        – Sten 80% hit ratio
        – rest ~95%

        100m:
        – Sten – 50% hit ratio
        – MP-40 – 60%
        – Thompson – 70%
        – rest ~90%

        150m:
        Sten – 30%
        MP-40 – 35%
        Thompson – 40%
        Beretta – 65%
        PPSh – 70%
        M56 – 80%

        200m :
        Sten – 10%
        MP-40 – 15%
        Thompson – 15%
        Beretta – 25%
        PPSh – 35%
        M56 – 45%

      • A very minor point. The M1 Thompson SMG is also slam fire weapon. The M1 has a separate firing pin mounted within the bolt, with the M1A1 the “pin” is a machined bump on the bolt face.

  11. Good luck with the bump fire practice. Great addition at the end to the video. Did you get a picture of what they were shooting?

  12. Great video! I noticed you had a number of instances where you had to cycle the rifle – was that an issue with the RPK or do you think it was just ammo related? Or perhaps something to do with the slide-fire process?

      • Were the issues only experienced when using the slidefire? If it was only experienced while using the slidefire it may be a timing issue. If you cycle the trigger faster than the bolt closes the hammer can follow the bolt down resulting in a light strike on the primer.

  13. I would recommend following these two threads on AR15.com. Most of these builds obviously focus on the AR15, but many of the concepts are the same when dealing with an RPK. I hope to set up an RPD in the next year or so.

    http://www.ar15.com/forums/t_3_118/655109_BumpSAW_Bump_IAR_Picture_Video_and_theoretical_discussion_thread_.html

    http://www.ar15.com/forums/t_1_5/1641834_M249_wannabe_in_OP___Official_Bump_SAW_bumpfire_stock_GD_thread__4_18_2015_.html&page=1

    Here is my rifle shooting 750 RPM with a 40rd PMAG.
    http://youtu.be/-kKWMqt6TnQ

  14. “You’re high.”

    “You’re high.”

    “You’re really high.”

    “You’re still high.”

    “You’re high, and right.”

    I giggled like a schoolgirl. Great video though! Wouldn’t a vertical forward grip of some sort be an aid here?

  15. I have not seen anyone successfully use a bipod and a slide fire stock.

    On another note there are some interesting spring front rail attachments that allow a front grip to move on a spring retracted rail making it easier to bump fire. I can’t find a link right now…

    • Jaqufrost posted a link with a lot of guns running bumpfire stocks on bipods. You should check the out or at least watch this. The concept is totally valid and been around for a few years now. I’m surprised it hasn’t taken off.

      http://youtu.be/e6eI6QpI4Ik

  16. Lmg’s, are for suppressive fire… Covering movement, it’s supposed to keep the enemies head down for awhile as you advance as is my understanding. You need a range where someone is hiding behind a “bullet proof” wall, and they raise a target periodically showing like it’s head and a bit of torso. Difficult to replicate as your not trying to avoid being shot, suppose you could have someone fire at it with a rifle while ducking and diving as you do moving forward. Then cover them to reload, see if you can put enough rounds down range to hit if they pop up. Psychology though, is absent in a target as it’s not going to die- You might well miss really, but there’s a risk in reality.

    • If your going over open ground, towards a enemy in cover, you have to fire from prone, up, down, up, down, like that, per shot more or less, in sequence with everyone else, covering each others reloads while moving forward. If your not on your belly, you’ve had it, as far as I know. But that goes for them, in that everytime they dont duck behind the cover they can get it. You have to be uber aggressive in a fluid motion, like a machine… Your a component part, the machine has pretty loose tolerances though and can finish minus you albeit shakely.

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