It really depends on how well the characters take care of their gear. your numbers seem to be assuming that the characters will
never clean their weapons, when any competent operator will do this every couple of hours in the worst sorts of conditions.
You are probably much better off trying to model 'instant' stuff that might make your weapon fail, rather than just assuming the PCs are illiterate savages that never maintain their weapons and gear.
this article is a pretty good demonstration of what difference proper care and cleaning can do.
So, for example, if the PCs are in the desert, and helicopters are flying over during a gunfight they are in, then you might ask them to make reliability rolls for their weapons. Of course, if a helicopter flies over while the PCs are just dicking around, then they will probably be cleaning their kit and cursing all chopper pilots shortly thereafter. If you are riding around in a helicopter, you put your weapon in a garbage bag or something to keep all the dust the chopper throws off from getting into it. Even just putting a condom or something over the muzzle during your chopper ride will help a lot.
The weapon reliability stats should largely be based on the basic weapon design itself. In addition, the reliability of the weapon has no direct relation to its price.
The 'marine' versions of various weapons are really for long term ship based duty. For example, standing watch in port to stop boarders. The fact that the weapon will be out next to the ocean for an 8 hour watch for at least days at the time would really impact a non-marine version of the same weapon. Just dragging your (regular) weapon out to have a firefight on a ship and then cleaning it afterwards won't make any difference it it's reliability or operational life.
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So what about the rules?
If the PCs weapons are exposed to bad environments during a firefight,
have them roll edge
+/- additional pool based on the reliability of weapon design they are using
- some dice, depending on how bad the condition are (Only up to -2 for the
worst possible conditions)
- some dice if they are using a particularly beat up weapon (-1 at worst, unless you built the gun out of parts from a junkyard)
- some dice if they are not taking proper care of their weapons (-1 if you just don't clean that often or well, -2 if you don't clean at all)
All the manual action weapons (bolt, break, pump, revolver) are very hard to screw up. Something like +3 dice on the reliability table.
Then, -2 to +2 based on the weapons basic design.
So note that a bolt action rifle know for its reliability will have between +4 to +5 dice to resist malfunctions. Even if the idiot conscript that carries it never cleans the rifle (-2), and it has been used to beat several people to death (-2 for being in bad shape), it will still be at +1 or +0 dice on a basic reliability test.
Also note that most weapon failures will not represent a broken weapon, but simply one that needs a little 'love' to get working again. Most failures will just take a simple action to feed the next round. Bad failures will requires 3-5 complex actions to fix. Only the most severe make the weapon completely useless.