Just a list of what guns I upgraded. Hope this helps you to what not to upgrade and what to. I can't remember all of the weapon upgrade names.
Colt-45 = a 8 round hand held rocket launcher
Kars98k = Armagedon = Just more powerful rifle and ammo capacity
G43 = G111 Compressor = More powerful rifle
Thompson = More powerful and more ammo cap
Mp40 = Afterburner = More power higher ammo cap
Trench gun = more power higher ammo cap
double barrel shotgun = 24gauge longrange = more power further zoom in smaller grouping of pellets
Type 100 = Untested
Magnum = Just stronger
PPSH41 = The reaper = more power higher ammo cap
BAR = untested
M1 carbine = Untested
M1 garandw/Grenadelauncher =The imploder = higher power higher Grenade count, Grenade has a magazine of 3 rounds per clip (you have 3 rounds per grenade per load instead of one)
STG43= Spats 447+ = more power higher ammo cap
MG42 = Baracuda = More power higher ammo cap
Browning 1919 = Accelerator = more power higher cap
FlameThrower = FIW nitrogen cooled = slightly lighter longer
PanzerShrek = Untested
Laser pistol = Porters x2 laser gun = more power higher ammo cap
Wanderwaffe = more range on zappyness and higher ammo cap
Right now I can't remember all the weapons. If you tested the guns I didn't test out yet please share :P.
o.O you need sandbag?
the BAR turns into the widow maker. it gets an increase in dmg and a higher rate of fire.
Thanks Boxer for the info on the Bar, By the way, the guns I think that are the most useful is the Colt, M1garand, mg42, browning , ppsh41, ray gun, wanderwaffe , shotguns, and STG(only reason so far is on how far it is at the Bunker, If ammo is really needed you can purchase more lol.)
o.O you need sandbag?
ya the PaP trench gun is beast. and it looks so sexy. the bar was suprisingly effective too.
oh and the type 100 upgraded turns into the 1001 samurai. it holds more ammo and does more dmg. i think it might have a faster ROF too but im not sure.
M1A1 when upgraded double clip size and WAAAAY more power...
Killin' zombies since day 1
PTRS = The Penetrator (hahahah) Increased damage and ammo.
PSN ID: [HSK] xmegazord
panzershrek i cant remember the name but it gets 3 rockets per reload so you can shoot 3 rockets fast without reloading (like the grenade launcher), you can run faster with it, and it seemed like it had reduced splash damage
the M1A1 turns into a automatic gun the clip stays the same size and you get more ammo and its stronger
30 Cal => B115 accelerator
BAR => The Widow Maker
Colt 45 => C-3000 b1at-ch35
Shotgun Double Barreled => 24 Bore long range
Shotgun Double Barreled Sawed Grip => The Snuff Box
FG42 => 420 Impeller
Gewehr43 = > G115 Compressor
M1A1 Carbine => Widdershins RC-1
M1Garand => M1000
MG42 => Barracuda FU-A11
MP40 => The Afterburner
.357 Magnum => .357 Plus 1 K1L-u
PPSh-41 => The Reaper
Shotgun => Gut Shot
STG-44 => Spatz-447 +
Thompson => Gibs-o-matic
Type 100 => 1001 Samurais
Type 99 => The Eviscerator
Panzerschrek => Longinus
PTRS-41 => The Penetrator
M7 Launcher => The Imploder
Kar98k => Armageddon
Ray Gun => Porterís X2 Ray Gun
Wunderwaffe DG-2 => Wunderwaffe DG-3 JZ
M2 Flamethrower => FIW Nitrogen cooled