Obviously, I'm in need of some help. I don't know nearly as much about weapons as I should, seeing as how nearly every single character of mine uses something on a regular basis.
First, some info on my main group of characters. They all use something. Literally. It's a nice mix of guns, knives, guns/knives. They all carry, with a few minor exceptions (their "Medic" is capable of using a gun without shooting himself in the foot on accident, but doesn't carry), and the ones that do carry never leave home without their favorite weapon(s) and extra ammo, and everyone has a stash of hidden weapons they can access quickly and easily should there be a security breach/break in. Less like "gun safe in my closet" and more like "shotgun hidden under the bar/counter" kind of weapons stash.
They have a lot of enemies.
And second, the dilemma. A character recently split off from the group. He has a lot of misplaced grief-fueled anger, and he feels betrayed by the group. He's been running with them for over a decade, but everything they've ever done for him and the fact they consider him to be a brother means literally nothing, seeing as how he's fixing to sell them out to their enemies.
He knows everything about them. He knows where they stash their weapons, who is carrying what at any point in time, he knows their schedule, he knows when they're vulnerable to attack, who the most capable fighters are, their fighting styles, when they're most likely to have their guard down, when they do routine maintenance of said guns/knives, he knows the layout--basically everything that takes away home field advantage for our boys.
He is going to tell their enemies everything, literally, so they can stage an attack in an attempt to wipe them out, and help them plan the attack. And in an effort to help take away that home field advantage, they're going to infiltrate and sabotage as many weapons as they can get away with before they make their attack. It's not often they get attacked at home, so they're not as aware of the state of their back up caches--not in comparison to what they carry every day.
So, the question: I need to know how someone can sabotage a gun and sabotage knives very quickly, in a way that could be easily missed. I especially need to figure out a way for this to cause injury (i.e. gun explodes in hand)--if it's not possible, even with a hand wave, I can easily think of another way to take someone partially out of commission, but this would just be more interesting.
I have literally every other detail worked out (most of the plan relies on the timing of the enemies), just not how they would go about conducting the actual sabotage. Their enemies will have access to literally whatever they would need to actually pull this off--the only thing is none of the weapons can be swapped. Most of my characters know their guns/knives very intimately, and can identify them by their nicks and scratches.
I know that heat/fire can really screw up a knife, but not if it would cause the blade to break. Mostly, on the knife related searches, I found out how to sharpen a knife properly and things about the edge of a good quality blade, but nothing that even implied how to sabotage it. The wrong ammo can cause problems, but not the extent of said problems. Also, I am aware of the classic "remove the firing pin" move.
And I don't need to know about the exact extent of injuries/treatment--it's a lot easier to find out that information.
Potentially relevant--in this universe, their tech all across the board is very sketchy. Some areas are more advanced, like medicine, and not so much in other areas. Tracer rounds for example are incredibly expensive, hard to come by, and usually can only be obtained by custom order via seedy arms dealer.
Appropriate weapons tags in this community.
"how to sabotage a gun" "how to make a gun backfire" "misfire causes gun" "how to weaken a knife blade" "knife damage causes" and the gun safety page on Wiki.
Thanks in advance for the help!