First a little description of what it is we see:
The gun is a large-ish sidearm that doesn't really look like anything we know from firearms history.
In order to be able to visibly fire on set, the "hero prop" was built around a Charter Arms Bulldog .44 Magnum revolver that could be loaded with blanks. It then has the cut-off receiver from a Steyr Mannlicher Model SL .222 bolt-action rifle screwed on top, the magazine from the Steyr attached below the barrel, plus some additional greeblies, as non-functional garnishings to build the outlandish shape of what we see on-screen.
Quite prominently, it also has (a) twin triggers in tandem, just like some versions of the Steyr rifle have IRL and (b) a number of LEDs at the bottom of the Steyr magazine.
From the OP's private collection. Image may not show in certain browsers.
EDIT: To show exactly what it is we're talking about:
Main parts of blaster prop — complete Blaster (OP's coll.), removed complete action of Steyr Mannlicher .222 Mod. SL rifle (with magazine; chamber portion of barrel visible), and a Charter Arms Bulldog .44 revolver. Note that bottom of rifle receiver and bolt are machined off to make room for pyrotechnic effect (i.e. revolver barrel), and the whole chamber and barrel of the rifle are removed.
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On screen, what we see of the gun being used tells us that:
- When fired, it produces a bright muzzle flash
- It also produces a loud report
- It doesn’t seem to support a very high rate of fire
- It can selectively fire explosive rounds
- In explosive mode, projectiles seem markedly slower than when firing non-explosive
- Engaging explosive mode takes too long to be feasible in "quick draw" situations
- In non-explosive mode, unless hit in the head, it seems to take several direct hits to "retire" a replicant
So what is it, in-world?
In early treatments, the gun was described as some sort of "black beam" gun (whatever that is), but what the propmakers built didn't satisfy Sir Ridley. So they built this instead. As they went through extreme lengths to disguise the revolver inside the prop, we can safely assume that it's not supposed to be a revolver in-world, either. It is also abundantly clear that it can't be a conventional pistol with a grip magazine.
Having considered various alternatives over the last 40 years, I eventually landed on the conclusion that it most probably needs to be a Gauss gun — a linear electromagnetic accelerator (not to be confused with a "rail gun").
I envision the Steyr receiver assembly housing the magazine of the gun, storing projectiles in a linear tube, in a manner resembling an inverted shotgun. The Steyr receiver's ejector port would be where you load the weapon, and the bolt handle is used to cock the weapon for the first shot; possibly also to de-cock it.
Operating the bolt handle moves the hindmost projectile from the magazine down to the chamber at the back end of the barrel. For subsequent shots, the reloading action might be either recoil operated or done by electrical actuators.
The Steyr magazine assembly houses the battery; the capacitors to drive the accelerator coils (which are embedded in the barrel) are housed in the bulge where the prop's revolver drum resides.
The muzzle flash and report are products of the electrical arc that occurs when the accelerator circuit is broken by the projectile leaving the barrel.
And what is the secondary trigger for?
To my mind, the most sensible use for it would be to activate the explosive projectile option. For a police weapon, it would make sense for the projectile to be inert by default, in order to avoid collateral damage in a civilian environment.
On the other hand, when hunting Replicants, having the ability to enhance the effectiveness of the projectile when you know that you have a clear shot would certainly be ... helpful.
I'm thinking that by engaging the secondary trigger, the Rep-Detect can elect to turn the projectile currently loaded in the chamber into a micro grenade.
Possible mechanisms for this might include injecting a chemical compound into a chamber in the bullet, or altering the composition of a material already there by introducing said chemical compound, and/or an electrical current, mechanically priming an impact fuse mechanism inside the bullet, or something similar.
(Alternatively, the weapon has a strictly limited number of explosive bullets — between one and three — stashed in a secondary magazine below the chamber, and pressing the secondary trigger returns the chambered round to the primary magazine, and swaps it for an explosive one.)
The slower projectile could then be accounted for by an added mass due to injected explosive compounds (or just a heavier projectile), and/or a deliberately lowered acceleration to not risk the projectile exploding in the barrel.
What does this mean in game terms?
I haven’t really made up my mind on exactly how I’d want to represent the gun in the game yet (there not existing a game yet). Therefore, for the moment, I’ll just settle for presenting a number of factors I see need to be taken into account in the process:
In ordinary "inert" mode, it should be possible to treat the weapon pretty much as a conventional pistol, never mind its outré design. I'd say it most likely can house about 8-12 rounds in its magazine.
As noted earlier, you probably couldn’t fire off a very rapid volley of shots with it, whether this be due to high recoil alone, or compounded by the recharging time of the capacitors.
It's the optional explosive round capability that renders it truly exotic...
Depending on how long one postulates it takes the mechanism that engages explosive mode to cycle, we might posit (a) that it takes a full turn to accomplish, (b) that it can be done in the same turn as the round is fired as a "minor action", or (c) that it can be done "for free" as part of an aimed attack action.
The only definitive limitation we know is that it is not possible to do in a "quick-draw" situation — e.g. with a Replicant bearing down on you doing flip-flops...
Another parameter to take into consideration is, is the explosive capability built into every bullet and merely primed by pressing the secondary trigger, or is the charge somehow fully or partially inserted into the chambered round?
If the former, the option can obviously be activated as many times as there are rounds in the magazine.
If the latter, there may be a limitation. In that case, how severe?
With the secondary magazine concept, the limitation is obvious.
Similar considerations pertain to the battery that drives the gun. I’m thinking that the LEDs might be indicators for the status of the battery and the explosive charges, assuming that the clip carries both.
Then there’s safety distance. At how close a target can you fire an explosive round without risking injury to yourself? On-screen, the explosion doesn’t seem extremely powerful, but it could certainly throw debris at you if you’re unlucky…