Concept: A Failfire, minus the fail

This is disappointing:

Thumbs up for the concept. Boo hiss for the execution.

This is going to be a long and rambly post. I'm thinking out loud here. Expect a wall of text and no pictures.

The Good

The Hailfire had the potential to be a good blaster. It's a support weapon that uses multiple standard magazines in a way that allows for ammo interchangeability with conventional 'rifleman' loadouts while maintaining a high capacity. It's lightweight (compared to a typical beltfed blaster of similar capacity) and has consistent feeding (which the alternative method of achieving a high capacity with moderate weight, bulk loading, does not have).

It's also snazzy-looking. That, however, is where the pros of the Hailfire end and the very long list of cons begins.

The Bad

Hoo boy. There's a lot to dislike here.

• Unreliable mag switching: The slip clutch slips too easily, including when attempting to switch magazines rapidly, resulting in a failed switch. 
• Slow mag switching: The only way to switch mags reliably is to do so slowly, and wait for the carousel to stop rattling afterwards. This is not significantly faster than a practiced mag swap in a more sanely-designed open-bolt blaster, and is likely to be significantly slower. The whole frickin' point of this blaster is quickly switching between mags, and it can't do the one thing that it was designed to do!
• Undesired mag switching: That slip clutch can also slip while running around, resulting in an unanticipated switch, potentially including switching back to a previously emptied mag.
• Janky mag retention: Mag retention relies on friction and on a spring-loaded nub that fits into the magazine's retention slot, with no positive locking. Oh, and that 'spring' is made out of plastic - the nubs are part of the same injection-molded piece that forms the core of the carousel, so mags can sometimes work loose.
• Prone to misfires: The slip clutch rears its ugly head again - but, in this case, blacklash in the rotor mechanism is also to blame. Running with this blaster can jostle the carousel out of alignment badly enough to cause darts to crash into the sides of the flywheel cage instead of being guided into the flywheels.
• . . . especially when turning quickly: Imagine the following situation: a zombie leaps out from hiding and charges you from the side. You quickly turn your blaster to zap that zed, but as you do so the carousel is pulled out of alignment by its inertia, resulting in a misfire. You die. Sucks, eh?
• . . . especially when loaded with heavy magazines: A high capacity is one of the most obvious advantages of this blaster, and loading it with larger magazines increases that advantage. However, heavy magazines exacerbate all of the above.
• Semi-auto: This is of course not necessarily bad considered in isolation, but it sits severely at odds with this blaster's intended role. 
• Inadequate support for modes of use other than hipfire: Hasbro seems to like designing their high-capacity blasters with hipfire in mind, and in this case it's understandable - how else could they make this blaster useable by people with short arms? There is a rail for attaching a foregrip at the front, but it is close enough to the carousel that its use would result in an uncomfortable collision between the user's wrist and a magazine.
• No support for a shoulder stock: This sorta makes sense in light of the hipfire-only concept, but that isn't how we want to use this blaster. Besides, even assuming hipfire, a stock can still be useful as an underarm brace.
• Weird flywheel cage design: The dart travels much further in this blaster before engaging the flywheels than would normally be expected. That's largely compensated for by the nice and smooth geared pusher mechanism, but it's still wasteful design. Maybe that extra travel is intended to counter the inaccuracy induced by an out-of-alignment carousel, but it would have been better to (a) fix the underlying problem instead and (b) if we do care about accuracy after all, not have dedicated hipfire.

(Not all of these are objectively problems - some people might like dedicated hipfire 'cause it's fun, for example - but all of these are reasons why I dislike the Hailfire.)

Many of these problems can be addressed simply by using the blaster in an unintended way - by holding the front magazine, securing it in position, and manually forcing the carousel to index. This is a fairly simple solution that, as far as I've heard, works well enough. With this, relatively straightforwards modifications (gluing the rotator mechanism so as to only leave the slip clutch free to move, adding a stock or other desired ergonomic features, etc.) can fix the other issues with the Hailfire.

However, it does leave something to be desired. The carousel is still large enough to create that aforementioned uncomfortable collision and interfere with ergonomics and maneuverability - and having to hold a magazine manually in position on order for the blaster to function reliably just . . . feels wrong. I'm reminded of a guy I knew back in 2010-ish who would hold his Stampede upside down so that old mags with weak springs would feed reliably. It was a simple solution that made good use of available materials and was, at least when compared to the direct alternative of holding that same Stampede the 'right' way up, very effective - but, eeeeeh. I say this with absolutely no disrespect intended to people who do things that way; I just don't like doing things that way.

More solutions become available when we entertain the possibility of rebuilding large portions of the blaster. A very sturdy rotor mechanism with positional locking could solve the problem of inertia, and placing a carousel on either side of the blaster would improve ergonomics while doubling the blaster's capacity. Both of these have already been done, and in the same build too:

This approach to 'fixing' the Hailfire is nice in many ways, but it is not without disadvantages. There's an inherent tradeoff in all blasters between capacity and bulk, and it leans very heavily on the side of capacity, with no good way to tilt the balance towards avoiding bulk. Using fewer magazines on each side would not significantly reduce the blaster's displacement but would only increase the wasted space within that displacement, using only small magazines would decrease endurance between swaps and negate compatibility with a typical rifleman's mags, and having a carousel on only one side would create a troublesomely funky weight distribution. As-is, weight-distribution issues may develop anyways if the blaster is only partially loaded. Overall, this is a cool build but there are good reasons why someone would want to do something different. That's what I'd like to do here: something different.

(There are also puzzling decisions specific to this build. Why retain the chainsaw grip, given that there is space for a pump grip instead? Why use a Hailfire as a base at all, given that every part aside from that grip, the shell, and the controls have been replaced? It looks like some opportunities were missed due to getting stuck in the "This is a modified X" conceptual rut. However, I'm supposed to be critiquing the Hailfire and not this build so I'll stop there.)

Both of the above ways of improving the Hailfire have disadvantages that stem from the geometry of the carousel itself. So: the carousel itself is a problem. More precisely, while the carousel is not the sole cause of any problem within the intended hipfire-only usage case of the Hailfire (it only exacerbates the unreliable and slow indexing because the total momentum that must be generated and dissipated when the magazines index is large; the fundamental cause of this problem is the play in the indexing mechanism), it becomes an ergonomic problem whenever this blaster is pushed out of that usage case.

This suggests an appealing avenue for a clean-sheet redesign of the Hailfire - get rid of the carousel, and use some other system for retaining and firing from multiple magazines!

The Ugly

Let's start by defining the problem:

• There are some number of magazines that must be retained by the blaster.
• The blaster must be capable of firing from (at least) one of these magazines at a time.
• The active magazine(s) must be switchable rapidly, preferably in a manner requiring only a single input from the user.
• Fresh magazines need to be able to be loaded into the blaster, and it should be possible to load any number of fresh magazines up to the number required to fill the blaster at any time.
• Expended magazines should be removable from the blaster. 
• Expended magazines should ideally be retained by the blaster until removed. However, I would regard it as acceptable if they automatically drop to the ground.
• There should ideally be a clear visual indicator tracking which magazines are fresh, active, and expended.
• All of the usual ergonomic and performance-related concerns apply as usual. This is a blaster that will see use in HvZ, so maneuverability and responsiveness are paramount.

This is an open-ended problem that leaves a lot of room for solutions ranging from the very simple to the very complex.

In the interest of simplicity, I'm going to start by assuming the use of a block of magazines that either remains stationary, or moves together. This retains one of the key advantages of the original Hailfire implementation: minimization of mechanical complexity. Normally, reloading a magazine-fed blaster requires two separate movements of the mags: removing the now-expended mag and then inserting the new one. Having a block of magazines that moves together means that these functions can be completed simultaneously in one motion. It also minimizes the number of moving parts, and makes it simple to ensure that fresh and expended magazines are clearly distinguishable.

I'm also going to tentatively assume the use of flywheels and an electronic pusher of some sort to fire the darts.

When selecting the configuration of these magazines, the primary concerns are to minimize the momentum that must be created and dissipated during each indexing event, and to fit a large number of magazines into a reasonable amount of space. Given that the size, shape, and mass of the magazines can be considered fixed for our purposes, packing them densely is not only helpful towards both goals, but in fact the only thing that can be done to further both goals.

This suggests a linear side-to-side stack of magazines, all facing forwards.

There is a soft limit to the number of magazines that such a blaster could hold - too many mags would result in a uncomfortably large blaster with an uncomfortably asymmetrical weight distribution when loaded with mostly fresh or mostly used magazines.

There are three ways that this could be accomplished that come readily to mind:

1. A series of magwells (or, perhaps they should be called magazine 'bays' sitting in a single magwell) could pass magazines from each to the next. This would require a fair number of moving parts per magazine - at a minimum, a set of latches to ensure that it only moves in one direction, and another set of latches on a moving sled to force each magazine along by one bay. This would be feasible to 3D print. It would require a lot of little springs, which is less than ideal but not a dealbreaker. The magazines might be vulnerable to twisting out of position - after all, there's nothing in that series of latches described earlier that prevents the front of the magazine from moving forwards further than the back or vice versa. Appropriately shaped latches would provide some protection against this, but not as much as locking, which would be difficult to implement.
2. The magwells themselves could move, and would then need to return back to the starting point. Effectively, we'd have replaced the wheel at the core of a Hailfire with tank treads. That probably doesn't sound like much of an improvement, but given that each 'magwell' could be a small structure that grips the back of a magazine by locking into the ridges on the sides, there could be only a single row of magazines, with very little space wasted by the empty magwells. There would need to be a mechanism that ensures that expended mags drop from the blaster to clear the 'wells' as they enter the rearward part of the track. Perhaps each magwell could span multiple links on a chain, the link between which would be able to bend only when they are positioned on the wheel at each side of the blaster, opening the aforementioned structure and allowing the magazine to drop free.
3. The magazines don't need to move at all - instead, the flywheels and pusher could move to rest atop each magazine in turn. This is . . . not quite as weird as it might initially sound. Of course, with a very large stack of magazines, this would have the effect of making the dart leave from a widely variable part of the blaster - but, with a reasonably small stack of magazines, the difference could be small enough to not be a problem. 

In any of the cases listed above, there would be a considerable amount of mechanical complexity. That means more carefully-shaped parts that need to be designed, more (fabricated? printed?) interfaces that need to fit together . . . and, once that's done, more opportunities for things to break and for debris or dirty mags or a bodyslam from an zombie or a dropped blaster to muck things up.

We need to simplify this concept in order to make it workable.

Good? Bad? I'm the one with the gun blaster!

So, let's simplify, take inspiration from real steel, and work by analogy. The most similar mechanism to idea #1 that is already in use is the lift mechanism that moves shotgun shells from integral tube mags in many pump-action shotguns. That's a difficult mechanism to get working. It's a viable mechanism, of course - even a popular one, in the context of pump-action shotguns - but it's not easy to make it run smoothly. The easiest shotgun loading mechanism to implement is a plain old break-action. The capacity of a break-action shotgun can be increased by having multiple complete firing mechanisms in parallel. Transferring that solution into the context of a multi-magazine blaster would suggest  . . .  well, something that I've already made. That's not a helpful idea. Let's try again.

Idea #2 is similar to the mechanism used in chain pistols, except that the empty 'chambers' (i.e. magwells) are automatically cleared of spent 'shells' (i.e. magazines). Chain pistols have fallen out of use in favor of magazine-fed or cylinder-fed pistols. Theoretically, chain pistols could offer a middle ground between the simplicity but low capacity of revolvers, and the high capacity but relative difficulty of implementation of magfed systems - but in practice, they haven't found a niche. Given the aforementioned soft limit on the number of magazines that is feasible, it seems that the best option would be one analogous to a revolver. This, in turn, would suggest a system similar to a Hailfire, or to the aforementioned dual-carousel variation thereof. Once again, this isn't a bad idea, but it isn't new either.

How about idea #3? Well, that's similar to a harmonica clip, except that it's the rest of the blaster that moves instead of the clip. A more conventional harmonica clip would be much simpler - and it would be fully feasible to have a harmonica clip that holds magazines! A brick of 3D printable magwells should be fairly easy to put together. The main disadvantage to this system would be that the magwells would not return to the starting position except by reversing direction. Reloading this blaster would therefore involve an extra step - pushing the clip back to bring the fresh magazines into position. That's not a major problem, though. It's a tradeoff that could be well worth it in light of the advantages of this system.

(We could also play off idea #3 by taking inspiration from clip-fed blasters and revolvers, and have the magazines arranged in such a way that their feeding positions are arranged in a circle, and have the firing mechanism rotate inside of that circle in order to switch active mags. Effectively, this would be to a revolver what idea #3 was to a harmonica clip. Much like idea #3 itself, this sounds very goofy, but I think that it could work. It is, however, not the concept that I'd like to pursue first.)

There are two more related decisions to be made: how the indexing mechanism is powered (motors? solenoids? manually? springs? etc.), and how it is triggered (thumb button as in a Stampede safety or Nitron mag release? pump action? reverse pump action? lever action? etc.). However, the viable options for the first of these questions will depend on the indexing mechanism used, and the viable options for the second will depend on the first. So, the selection of an indexing mechanism is the first problem that needs to be solved . . .

. . . and there's an obvious solution: ratchet grooves on the top of the harmonica clip connecting to a pump grip at the front would provide a simple and easy way to index it. Specifically, I'm thinking of ratchet grooves of the same general form as seen on the drum of a Webley-Fosbery revolver, because they could be reverse-indexed in a controlled manner by pushing the clip while pumping the charging handle. In other words, the grooves would be specifically not like those seen on the rotor of a Strongarm, because those can't be reverse-indexed as easily.

This naturally lends itself to either a pump-action or reverse pump-action system. I'd prefer regular pump-action, but there's no reason why the same blaster couldn't accommodate either with different clips with differing patterns of ratchet grooves. Assuming a right-handed user, I think that it would be better to have the clip index to the left, with spent mags on the left side of the blaster. That would make it easier to access and replace the spent mags, and to push the clip back into the blaster while pumping the foregrip in order to reverse-index it in a controlled manner.

This system has the incidental advantage of possibly allowing the whole clip to come out, for a relatively quick complete reload. There's also no reason why the same blaster couldn't accommodate clips of multiple sizes, in order to move up and down the sliding scale of wieldyness vs capacity, and  multiple clips that accept different magazine types. Say, for example, you don't want to use Worker 40-rounders all of the time, due to the fact that they tend to choke on mixed dart types or ammo that is less than perfect and do bad things for velocity and consistency - it would still be nice to have the ability to save some fresh ammo and throw in a clip of them in for the final stand, eh?

 "Clipazines," eh?

Yes, this is amusing.

For those unaware, there was a tempest in a teapot a few years ago on /r/nerf about whether magazines should be referred to as clips. This wasn't just about the use of 'clip' as a non-technical colloquialism - some people went so far as to argue that 'clip' is the correct term for nerf mags. During this debate, the term 'clipazine' was presented as a compromise that neither side really liked.

So, here we have an idea for a magazine-fed blaster that is also clip-fed, as it uses a harmonica clip that holds magazines. Finally, here is a context where the word "clipazine" makes sense!

Further refinements

There are other mechanisms that could be used to drive the clip, which may be more convenient than a pump handle.

• A linear indexing Geneva drive comes readily to mind. This would be good if mag switching were to be electronically controlled.
• A simple rack and pinion used with a stepper motor is also an obvious solution, although given the risk of it failing with the clip out of alignment with no obvious signs of failure, perhaps not a good one. 
• A manual lever-action system would free the area under the front of the blaster for something underslung. Given the amount of firepower already available, it's unlikely that an underslung integration would be desirable except as a special projectile launcher for dealing which shields, special zombies, etc. - but it would still be nice to be able to add such a launcher for such purposes. However, a lever-action blaster would be both slightly more complex and harder to reverse-index. 
• Likewise, a system similar to a forwards-accessible charging handle would free the area under the front, although it would make mag switching a bit slower as it would require an additional hand movement.

A pump-action system combines minimal hand movement per switch with minimal complexity, so that's what's going in version 1 - but I'm considering any and all of the above for version 2.

Thus far I've assumed that a flywheel system of some sort would be used despite the fact that (almost) any firing mechanism could be used with this system - that's possibly a case of "This is a modified X" but it's not just a case of that. Flywheels are a good system for producing automatic fire. Importantly here, they are also less sensitive than breech-and-bolt systems to slight magazine misalignment. Mag misalignment is not good for accuracy, of course, but at least the blaster will still fire. So, at least for v1 and possibly all future versions, that stays.

What's next?

I'll slowly put together a design. This is likely to turn into another one of those long-term projects where progress is slow, but the end result is worth it.