Experimental .30-40 Trapdoor Springfield Repro (Video)

We have often touched on the series of US magazine rifle trials that took place through the late 1800s – those trials brought out a slew of interesting new ideas and clever (or not so clever) designs. However, the trials were also responsible for an experimental version of the old standby Allin conversion Trapdoor Springfield.

In order to have some rational standard to judge the new rifles against in the later trials (after the .30 Army, aka .30-40, cartridge had been specified instead of the old .45-70), the Ordnance Department decided to rebarrel a handful of Trapdoor rifles for the .30-40 cartridge. These would act as the baseline against which the recoil, accuracy, rate of fire, handling, etc of the new designs would be judged. Few if any of those original conversion exist today (I have not ever seen one, but I suspect one or two are probably in museum collections somewhere), but I did have the opportunity to try out a modern reproduction of the pattern made from original parts.

23 Comments

  1. If it’s a twice converted blackpowder rifle, can it still safely fire a 30-40 smokeless for a long time? I am not seeing my self shooting nitro from a Beaumont Vitali, so why should this be a safe idea?

    • I’m not sure that the united state iteration of the Krag, their low number Springfields – or even their 1980s Berreta pistols, offered you any better guarantee.

      I suspect that so long as the hinge pin doesn’t let go, that there is sufficeint inertia in the trapdoor for it to happily work in a similar fashion to a blowback.

      It would be interesting to know how much stretching is going on in those cases, to get some idea of how much of the stress of firing is being taken by the case itself, rather than by the trapdoor.

      • I hate to say this, but the Allin breech (the correct name for the “trapdoor”) was probably the weakest of the “conversion-breech” systems.

        Basically, the “cam lock” as it was described relied on two things to hold it shut. Those being the spring-loaded catch and the hammer hitting the firing pin- the latter on the principle of the downforce of the hammer, driven by its spring, acting against the front hinge’s upward rotation at firing.

        If the spring-catch failed, the breech pressure generally overcame the hammer’s inertia and spring, forcing the breech to pop open while there was still pressure in the chamber. The result was usually a case-head separation and the shooter getting a faceful of hot brass and hotter gas.

        In one Gun Digest Annual one writer (who shall remain nameless) waxed rhapsodic about the superiority of the trapdoor breech over the Remington rolling block on safety grounds, because (by his admission) the trapdoor breech invariably failed before the barrel split at the chamber. Which is absolutely true. The Rider-designed breech is famous for staying shut even with overloads that burst the barrel. In one test in France, a standard rolling-block rifle was loaded literally from breech to muzzle with over thirty bullets, a series of wads, and a triple powder-charge. It was then fired (with a lanyard!) from behind an armored screen. The French experts reported laconically, “Nothing extraordinary happened”. Well, except to the target, which looked rather like it had gotten on the wrong end of a six-pounder firing canister.

        The “weak” Remington breech repeatedly survived such abuse in tests. The Allin breech has a discomforting habit of failing with service loads in .45-70, as the Gun Digest Annual article shows with photographs. With the barrel generally remaining intact, even at the chamber, because all pressure is vented straight out the breech when the spring-latch and hammer don’t succeed in keeping it shut. Or else the hinge-pin fails, too, which leads to a really exciting-looking failure at about .280 Ross Rifle levels.

        I leave it to you to gauge the judgement of someone like the writer, who thinks a breech failure endangering the shooter is “safer” than a chamber split that vents the gases, etc., out to the side.

        I suspect the main reason the parsimonious Congress didn’t order the Army to convert trapdoors to .30-40 for the Reserve and National Guard was that Ordnance realized that the Allin breech, designed originally for a .58 rimfire and then altered to first the higher-pressured .50-70 and then the even more pressure-emphatic .45-70 rounds, was skating into its (minimal) safety factor with the smokeless .30-40 loads.

        By comparison, the British 0.577in Snider-Enfield was probably the strongest of all the “conversion” breech actions. With its hinge parallel to the bore, and a spring-catch that really only served to keep the breech from falling open when inverted, it was essentially a square steel “brick” inside a square steel “box”. To force the breech open in firing, the pressure would have been required to compress steel upon steel, and that just wasn’t going to happen. I’ve never seen or heard of a Snider converted to 0.303in, but I suspect it would have been a good bit safer than a trapdoor converted to .30-40.

        BTW, Erskine Allin, who designed the trapdoor (“borrowing” a lot of its features from Col. Hiram Berdan’s “Berdan 1” as sold to the Tsar) was director of Springfield Armory at the time of the Ordnance Board competition to choose a new “conversion” breechloading rifle (late 1865). Jacob Snider was one of his design engineers. Both were serving officers.

        When Snider tried to enter his breech design in the competition, Allin charged him with insubordination and had him drummed out of the service. Allin then went on to “win” the competition with the trapdoor.

        Snider, concluding that his services weren’t wanted here at home, did what so many American arms designers would do in the last half of the Nineteenth Century. He went to Europe. And presented his design to the British Army ordnance department, which was also looking for a way to convert muzzle-loading rifle-muskets to metallic-cartridge breechloaders at the time.

        As they say, the rest is history.

        cheers

        eon

        • Thanks for setting that one straight, eon.

          There’s a discussion somewhere in Julian Hatcher’s work about how much load actually makes it back onto a breech block. He concluded that with some stretch actions, in certain chamberings, that the answer can be not very much at all. I believe he experimented with a Winchester 94 .30-30, modified to remove the locking parts (I’m assuming with a string to fire it) and found that with .30-30, the case will actually hold itself in the chamber.

          Simillarly, although in bright sunlight so we didn’t get to see any flash, Ian’s experiment with an unlocked Ross in .303 although still nasty, was less spectacular than I think many of us were expecting it to be.

          The failure mode for the British replacement for the Snider, the Martini was a split barrel too, possibly (like some particularly serious Mauser ’98 KBs) continuing back to split the receiver ring.

          It’s interesting that even in the hyper litigious united state, some high level custom gunsmiths were rebarrelling small BSA Martini actions to .30-30 headsize rounds, although they did caution the owners not to exceed factory .30-30 pressure levels – more due to the small diameter of the barrel shank, than any worry about the breech block or the receiver letting go.

          I gather with .222 head size, including wildcats on the German 5.6x50mm, you could go as hot as the primers and case heads would stand – should anyone actually want to, rather than buy a .22-250 instead (I contend that the big reasons for the .222 having such a good reputation for accuracy and good shooting even when compared to .223, is the .222’s 40k cup pressure compared to the 55k to 60 k+ for the .223).

  2. Nice rifle, was the U.S one of the first to go for .30 cal as a military calibre, out of interest or one of the last. The British had .450 prior to the .303, 45/70 – 30/40, the Germans had a 11 something millimeter calibre also I think, I kinda imagine the U.S being last to down size so to speak.

    If you had a .50 Beowulf calibre AR platform and you rigged up a API mechanism to use in conjunction with it’s parts, so the recoil spring was going forward when it fired how much more resistance would the spring need to have roughly out of interest. Would it be equivalent to two recoil springs, four or, anyone know approximately? Because the bolt wouldn’t be locked would it, so I assume a conventional spring wouldn’t suffice. I am trying to ascertain would the cocking handle need to be more like a sidelever air rifle than the usual variety, kind of topical carbine rounds…

      • Thanks Keith, I will have to get that book or download it on a computer, I am using a phone. I found a synopsis of a relevant chapter on the link you provided, Becker cannon, Oerlikon types. It mentioned one 20mm gun I think of having a recoil force of 70kg, 70kg is 150 odd pounds in weight. Formulas hmmm, scratch… Er, one sidelever RWS 48 has a cocking pull of 39lbs, I read on a website recoil buffers can get the Beowulf to have a recoil force of about 34 ft lbs however it mentioned the gas pressure at the muzzle was about 5000 lbs. Now I can see some correlation between the numbers 39 and 34 but not necessarily the llbs – ft llbs part of the equation so to speak. Looking at that Oerlikon, it is quite large so it could have a large spring/weight in it. But it must be a force of 70kg not whatever thousand of pounds of gas pressure that is at the muzzle, and as it’s not locked being Api so that must be it’s spring resistance presumably given it said someone had to cock it also. Therefore maybe that side lever spring would be about right for the Beowulf, although I’m not sure. I’m suggesting using a modified Beowulf barrel for Api, stuck on the front of the RWS essentially with it’s piston replaced with a Api bolt of the appropriate weight? If the spring is right’ish, as a test. The case you see looks suitable unlike any other “small arms” case I can find.

        • The relative masses of breech bolt and of projectile are the important factors. Springs rates are calculated after the masses are determined.

          mass1 X velocety1 = Mass 2 x velocety2

          let’s say that the bolt weighs 100 times what the combined bullet and half the powder charge weighs.

          Then for every 10cm that the bullet travels, the bolt travels 1mm. for simple blowback and assuming an allowable travel of 3mm for the case before the web comes out of the chamber, that limits you to a maximum of 30cm barrel length.

          Even with API, you also need sufficeint bolt weight to keep the case head safely in the chamber if you suffer a hang fire, and sufficeint buffering to safely stop the recoiling bolt after that.

          For advance primer ignition, the spring strength is then worked out in order to accellerate the bolt for feeding and firing, and to decelerate it so that the sear catches it when it is only moving with minimal velocety,

          you can use some sort of buffer to soak up any remaining bolt momentum when it passes a little way beyond full cock.

          This will get you up to speed on springs http://www.bookdepository.com/Spring-Design-Manufacture-Tubal-Cain/9780852429259

          If you use his calcs for IC engine poppet valve springs, you’ll get the idea.

          There’s also an article somewhere by Hiroaka about spring calcs with a method of calculating how much they’ll expand when you take them off the mandrel.

          • Incidentally, with the workshop practice books, the lower number books in the series tend to cover the ground in better detail, some of the later ones (sy from the mid 30s) are shallow “me too” efforts in comparison to Tubalcain, Hart, Ivan Law etc.

            If you’re on a low budget, British public libraries often have a selection of them.

        • With API, you will also need to work on how to allow a case to move without separating.

          the critical shear stress (when movement just begins) = normal stress x tan friction angle.

          Varmint al has experimental determinations of friction between steel and brass

          what you need to determin is how to reduce normal stress

          Traditionally (oerlikon cannon – Ian has the manual for one on this site) grease was used,

          chamber fluting allows some of the hot chamber gas to get outside the case to help counter the pressure within it (that’s partly what the grease did)

          With API, that gets interesting, and you may find that only the front section of the chamber needs to be fluted, as chamber pressure will have dropped by the time the case has only moved a short distance.

          If you find that you need fluting for a greater length than the cas length, then you’ll have the problem of designing an extractor that doesn’t get blown off

          You’ll also need to make sure that you don’t get gas blowing past the bullet – you may have to use a special bullet with exposed drive bands which engage the rifling before firing – that will make extracting a live round interesting, as the bullet is likely to pull out of the case, spilling propellant everywhere.

          you’ll enjoy working it out.

        • For suitable case head forms, there was a US patent by the O’Connor Rifle Company for converting existing brass cases with new screw on steel heads, I don’t think that the idea was in any way or form a commercial success. Check the idea out, I think the patent should have expired by now, and it would give you a way to use existing drawn brass case bodies with unusual head styles.

          Another patent (probably also expired by now) was by dick Cassul of revolver fame, and covered a female style case head, similar to the one shown in the gunwriters.fi article.

          one for you to ponder, is the possibility of an extractor cut in the chamber wall, and bleeding sufficeint gas into that cut to stop the case from bursting into it, and designing an extractor capable of putting up with such mis treatment, and likely a couple of sealing grooves like a gas piston has, on the part of the bolt head which enters the chamber. That way you could use conventional ammunition with a full diameter rim in an API action.

          Incidentally, it’s worth checking out old Oerlikon patents for the striker tripping mechanisms to avoid the gun from slam firing if the striker breaks.

    • The trend started with the Austrians around 1885 but their 8mm round was still black powder. The French were the first smokeless 8mm in 1886, followed by the British and Germans 1888. The US was again late to jump on the bandwagon.

  3. There is not much difference in peak bolt thrust between the .30-40 Krag and .45-70 Springfield cartridges. The .30-40 cartridge generates about 1,500 lbf peak thrust; the .45-70 cartridge generates about 1,450 lbf peak thrust. The higher pressure of the .30-40 cartridge is offset by its smaller head diameter, which is why the peak thrusts are so similar. The higher velocity and sharper pressure curve of the .30-40 cartridge result in this peak thrust being delivered for a shorter period of time, mitigating the slightly higher peak thrust.

    Bolt thrust at any instant is calculated by multiplying internal pressure by case maximum internal area (pie * r**2). Similar to piston force calculations in combustion engines or hydraulic cylinders. Just be certain to use common units (metric or imperial).

  4. Interesting Video Ian.
    You sure are kind to bring us items that are off the well worn beaten path.
    Thank you.
    I had no idea the US military had converted a few (how many?) trapdoor carbines into 30-40 Krags!
    And now for three inquires.
    1. Maybe I missed it but who built your new 30-40 “Springfield” trap-door experimental carbine?
    2. Is it an import….from Italy maybe?
    3. What price are the reproductions selling for (new and used)?
    4. Since my 45-70 trapdoor Italian Pedersoli has a retractable firing pin (not a floating one found on the original 45-70 Springfield’s), does your reproduction carbine also have the retractable spring loaded firing pin?
    Regards
    Spotted Cat Weapontry

  5. The 30-40 trapdoors built at Springfield were not conversions of 45-70s but were specially built on heavier receivers and used the “positive cam action”.

  6. Do you not think .50 Beowulf would work, it has a rebated rim but do you think it’s base section isn’t up to it ie. it might fold around the rim sort of thing “it could be fairly well supported by the bolt face” 30x98RB you could kind of copy that, cut a 88grm Co2 cartridges top off and fill in the base with say brass to reinforce it thread the outer fit some sort of rim in the rebated manner.

    Better if .50 Beowulf worked, anyway purely theoretical for me. I will attempt to create a drawing with hypothetically correct springs etc via reading more about such things, then possibly make a wooden model perhaps with a shrunken 30x98rb pretend case out of polymer clay or something he he.

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