My calculations indicate that an expendable weapon's durability bar lasts for 5 gameplay hours. (This was tested using durability loss on an AK47 over 20 minutes of PB Rescue. If durability loss is somehow different otherwise... >_>). I'm not sure how it applies to other pieces of equipment or permanent weapon mods since expendable 08 armor and such seem to last a lot longer for some reason, so I'm going to test that. However, I'm pretty sure all expendable weapons follow this trend. What does this "5 hour" figure mean?
Before I start the following calculations, I'll say that
-a typical gun costs 300-400 euros per hour to repair (this is ignoring permanent weapon mod durability, which I haven't figured out yet. Let's assume we're using an M4MK3 or AKMK3 with no mods)
-a player gains a base rate of 48 sp per minute in PVP not including badges, which equates to 720 euros per hour or 1 supply case worth 5000 euros every 7ish hours. If we throw in badges into the equation, we might end up with 5000 euros every 6 hours or so, or maybe even 5 if we're talking about pro marksmen who grind Annihilation 80. (Oh yea, if you didn't know, a supply case takes ~7 hours worth of base PVP SP gain to reach 100% - this is excluding badges)
If you use an M4A1 MK2 expendable with rich-man's mods (4870 euros for 5 hours) when you could have been using a typical weapon that costs around 2000 euros per 5 hours to repair with a euro gain rate of ~4000 euros per 5 hours via supply cases:
with the M4A1, you are netting a LOSS of 800-900 euros over its lifespan
with the modless permanent euro shop gun, you are netting a gain of ~2000 euros over 5 gameplay hours
When using an exp Bizon (4220 euros) for 3-box farming with a base gain of 27 sp/minute and an average of 8 gameplay minutes (under average circumstances) to get all 3 boxes;
You gain ~2000 euros worth of supply points from the sp alone
You gain ~19k euros from green boxes (assuming a 100% success rate)
You end up with a total profit of ~16.5k euros for 5 gameplay hours worth of farming, as opposed to ~21k euros for using a timed stg/ppsh instead.
If pistols follow this same trend, using an expendable glock costs 200 euros per gameplay hour as opposed to using a perm pistol that typically costs 60-70 euros per gameplay hour to repair
Moral of the story: Buy M4A1 MK2 perm. Or MP5K PDW perm, if you ever get around to respecting how AWESOME that gun is.
And I will continue to keep testing other things such as permanent weapon mods, 08 gear, and sidearms to see how they differ.
Edit: btw, since 10 expendables = perm, it takes you 50 hours to level the costs between expendable and perm. If you have mods, the costs can easily take 70ish hours to make up or more.