Mechanical engineering question

[pmlizardmen]

So I was wondering if anyone had a degree in mechanical engineering? If so I was wondering if a auto reloading crossbow is possible? As if I can build it I can have a guy in D&D/pathfinder build it

[kegcarrier]

I'm not a MechE but the problem I see is how to power the reload mechanism. Guns divert gas from the exploding round to push back the bolt carrier, eject the spent cartridge, and pull another round out of the magazine.

[stonecutter]

While I am not a mechanical engineer, I am an industrial engineer so I may be able to shed some light. Kegcarriers observation outlines the main problem of any repeater weapon - how to get the firing mechanism into place to allow the next round to be fired. The process is relatively easy for firearms as each "round" provides it own propulsion system in the form of gunpowder. Unfortunately, bows (both crossbows & regular bows) rely on spring tension in the weapon itself to fire what is essentially an inert projectile. In terms of mechanics, I see two options:

1) Real World Solution - The Carousel: This would involve creating a cylinder (aka carousel) of pre-loaded bolts. The carousel would have a compressed spring/torsion device for each bolt and they would be arranged in a manner similar to that of the old western 6-shooter pistols. As each bolt was fired, there would be sufficient energy not only to propel the bolt itself but to rotate the carousel into position so that the next bolt could be fired. Once the 6 shots (or whatever number was constructed) were fired, another carousel would be loaded onto the crossbow. During down time, the carousels could be re-cocked and loaded with new bolts. Obviously, this would be a rather heavy and cumbersome device as it would effectively have 6 times the spring/torsion devices of a normal crossbow.

2) Pathfinder/DnD Solution - Magic. A self-loading crossbow removes the main problem of getting the spring back into place to fire the next bolt without having to physically do the work. In this instance, a simple ammunition "clip" of several bolts could be loaded onto the weapon and it would work just like a modern repeating firearm in that the autoloading crossbow would draw each bolt into position until the clip was empty, at which point a new clip could be added. This would be more complicated and heavy than a standard crossbow due to multiple bolts and the ammunition clip itself but much better than the carousel solution.

[voodoo]

If your GM will allow it you could take a standard repeating crossbow already outlined in Pathfinder and cast Abundant Ammunition on the bolt carrier then a permanency spell on the abundant ammunition spell (which doesn’t normally allow for permanency hence GM discretion) That way you’d have a constantly reloading bolt carrier with a standard repeating crossbow.

[pmlizardmen]

Thanks guys I will run both options past my DM. Also I'm so shocked that I actually got a real world way to have one lol