It's an excerpt from this book: http://www.amazon.com/gp/product/1599638150
Firearms and knives in the real world are often tweaked for specific
purposes, but heres a little secret: The more tricked out the gun or
knife, the less practical it becomes.
Every accessory, modification or addition of something cool narrows the function of the gun or knife.
Theres a reason the most popular firearms and knives in reality are
also the most mundane. Simplicity equals versatility, and Im betting
your characters require a truckload of the latter.
Which do you use more often on a daily basis: a steak knife or a
Swiss Army Knife? The steak knife might be intended for cutting meat,
but you probably use it for scores of other tasks, from prepping
vegetables to opening mail.
Despite all the roles it tries to fill, the Swiss Army Knife is
actually less functional from a practical standpoint. It requires a
specific need before its used.
Instead of creating a crossbow that fires arrows and bombs and
uses a backup pistol embedded in the design, stick to a dedicated
weapon that can do a single thing well. Give the character a separate
backup pistol instead of building it into the crossbow.