Editing Bolter (section)

==Recoil==
The power of a Boltgun has been exaggerated and hyped up for years, mostly under the '''''Rule of Cool'''''. This extends as well to the recoil. The fact that bolts are rockets and not traditional bullets sometimes gives rise to fan-arguments. Since one of the big advantages of Gyrojets is a lack of recoil, some fans believe that a Bolter shouldn't have any either. However, Gyrojets suffer from a very low muzzle velocity, as the rocket needs to get up to speed. As mentioned earlier, Bolters get around this problem with a more traditional initial propellant explosion, and that '''does''' cause the gun to kick like a normal firearm. The recoil is said in some sources to be enough to tear a normal human's arms off, or send them flipping tit over toe. However, there is evidence to suggest that this is either simply in-universe propaganda, or depreciated older edition "''Marines are so super cool''" fluff, such as the fact that unaugmented Imperial Guard officers are able to use bolters without the aid of Power Armour. Per the rules in the Fantasy Flight Games RPGs, unaugmented mortals can actually use Astartes-grade Boltguns, but count them as heavy weapons; Astartes Bolt Pistols count as rifles. Even then, only those with a relatively high Strength score can fire them without heavy penalties to their accuracy, and there will be some penalties as the weapon is just too big for regular human hands. Firing a Space Marine weapon will incur a penalty as well, since Astartes Boltguns tend to explode in the hands of anyone other than a Space Marine, allegedly due to gene-sensing booby traps. The machine spirits are very picky about their users.

The basic issue in question is whether the actual recoil can be judged since there is no solid information on the mass and velocity of the bolts, not to mention the mass of the bolter or any recoil-dampening systems it may have. That said, some basic assumptions can be made about the weapon. First is that Astartes Bolters fire .75 or 19mm-ish projectiles. This immediately puts the Bolter out of tangible comparison to almost any modern firearm with the notable exception of magnum 12 Gauge (''.73 or 18mm-ish'') slugs, or even the less common 10 Gauge (.76 or 19mm-ish) slugs. But while it is tempting to take a look at the AA-12 automatic shotgun's very low recoil and call it a day, these are shotgun cartridges, and are lower velocity compared to rifles. The only real comparison in terms of a "conventional" style rifle would be some high powered "Elephant guns," a class made for big game you need to put down with a single shot such as the .557 "Tyrannosaur" rounds, which is a massive 14.9mms. And yes, it seems to have been named by a five-year-old. [https://www.youtube.com/watch?v=wrImp-ek3bI This is what happens when you shoot one of those]: note how 9 times out of 10 the gun jumps out of the shooter's hands. Considering that the standard propellant charge is sufficient for effective terminal performance at short range, so... a figure of at least 3,000 ft/lbs or a 438 grain projectile leaving the barrel at 1750 ft/s should be a solid minimum. This kind of performance produces recoil that is manageable but capable of knocking a shoulder out of its socket. Not that this performance is the minimum. There are also several available super-magnum pistol cartridges that perform comparably, which means an Astartes Bolt Pistol is entirely feasible in the real world. On the other hand, non-Astartes Bolters have been described by some sources as 12.7mm or .50 projectiles. The performance of full-sized non-Astartes Bolters can be judged at .50-70 performance, which will be about a 450 grain at 1250 fps (1500 ft/lbs) as a minimum. It will still be stiff but tolerable. By that logic, non-Astartes Bolt Pistols could theoretically be at around the .500 S&W Special (''350 grain at 1,100 fps for 941 ft/lb''), so, again, stiff but plausible.

However, remember that a Bolter's initial charge is not necessarily meant to propel the bolt to maximum speed on its own, nor is a bolt round ever said to travel as fast as a rifle round. So somewhere in the middle of the 10 gauge shotgun and the T-Rex gun is a pretty reasonable guess, but that's a wide gap. You can narrow it when you consider that the bolter is not a gun: it's more akin to an automatic rocket launcher/gun hybrid since the bolts are, well rockets. While we do have a working example of a rocket gun of this kind, the gyrojet, its highest caliber was .49, not close to the bolter's .75, so basing recoil off of that is impractical. Additionally, the gyrojet was designed with an open "chamber" and "barrel" (really, just an open frame to keep the projectile in place and pointing forward), so that none of the exhaust gasses from the rocket would impart force on the frame itself, whereas bolters appear to be fully contained and would theoretically built up gas pressure inside like a conventional gun. In any case, considering the rocket nature of the bolter it's probably closer to the 10 gauge than the T-rex gun.

Now, we get into the weight and materials of the guns themselves. Heavier guns absorb more recoil just from laws of inertia—which is something video games usually do backwards because it sucks when your starting pistol has high muzzle climb—and 40k has always been big on the boxy heavy guns, partly because of the limitations of [[Miniature|28mm scale]], and partly because this is a universe with flaming chainsaw swords, you need big guns for big battles. Older fluff illustrations put an unloaded Validus-pattern Bolt Pistol at 1.75 kg... God-Emperor knows how much for loaded. The S&W Model 500 clocks in at 1.6 kg unloaded and 2.25 kg loaded, giving us a halfway decent benchmark on what to expect from recoil absorption. These are all educated guesses, but it is better than just blind arguing. With that being said, there is another, somewhat similar weapon in existence. The XM25 Counter Defilade Target Engagement (CDTE) System, while a grenade launcher, fires much, much, slower velocities than those theorized above. It shows that such a weapon is feasible, and in some sense, may actually be fire-able for a conventional human. Furthermore, considering the size and materials of a Boltgun, the recoil felt will be considerably less than an elephant gun in acceleration terms, and so while definitely impractical and uncomfortable, it is most definitely fire-able. Bearing in mind that part of the advantage for such a weapon is reduced recoil. Considering design and construction examples above, one can argue that a .50 version will have the same general recoil as .50 Beowulf or similar cartridges.

Alternatively, the weapon could function similarly to the [https://en.wikipedia.org/wiki/Neopup_PAW-20 Neopup]/[https://www.youtube.com/watch?v=QHbqHx3TLBE Inkunzi PAW-20], a 20 mm direct-fire grenade launcher. With a 20mm x 42mm, 330 gram projectile designed to travel at 310 m/s or 1000 ft/s, it's pretty close to what a bolter could be in a real world platform. The PAW-20 has a inertial recoil system, with a massive spring that basically compacts into the stock to absorb recoil. That said, a bolter with a heavy .75 caliber/19mm round and a relatively short barrel would probably produce surprisingly low recoil given the kicker charge and most of the projectile's force would be from that rocket motor. Incidentally, novelizations have described the report as a two-part boom, although given the kicker charge is supposed to ignite the rocket motor, there probably wouldn't be a discernable gap for unaugmented humans.