*The information below has been gleaned from various posts from other sites and has not been vetted by this poster. This is intended for informational purposes only*
I though this information would be useful to those individuals desiring to put aside ammunition for a "rainy day". Please feel free to add to or comment.
The addition of some desiccant would be advisable for long term storage
REPORTED CAPACITIES FOR STANDARD / COMMONLY-AVAILABLE AMMO CANS
9mm Luger

30 caliber ammo can, loose – approximately 1,200 rounds
50 caliber ammo can, loose – approximately 2,200 rounds

45 Auto

30 caliber ammo can, loose – approximately 770 rounds
50 caliber ammo can, loose – approximately 1,300 rounds

40 S&W

30 caliber ammo can, loose – approximately 1,000 rounds
50 caliber ammo can, loose – approximately 1,750 rounds

5.56mm NATO

30 caliber ammo can, loose – approximately 600 rounds
50 caliber ammo can, loose – approximately 1,100 to 1,200 rounds
TALL 50 caliber ammo can – 20 loaded Magpul P-Mags (600 rounds)
TALL 50 caliber ammo can – 24 standard AR magazines (720 rounds)

7.62mm NATO (308 Winchester)
Note that this would be about the same for ANY ammo built on the 308 case (243 Win., etc…)

30 caliber ammo can, loose – approximately 320 rounds
50 caliber ammo can, loose – approximately 640-700 rounds

7.62x39mm Soviet

30 caliber ammo can, loose – approximately 500 rounds
50 caliber ammo can, loose – approximately 900 rounds (based on a math calc)
50 caliber ammo can – 1,000 rounds of BOXED Wolf-brand ammunition (or similar box size)
50 caliber ammo can – 840 rounds on stripper clips
50 caliber ammo can – 11 (eleven) 30 round magazines (with one being on top) (330 rounds)
TALL 50 caliber ammo can – 20 (twenty) 30 round magazines (600 rounds)
WIDE 50 caliber ammo can (SAW Can) - 24 (twenty-four) 30 round magazines (720 rounds)
40mm Can, boxed – 1,920 rounds (would be heavy)


5.45x39mm Soviet

30 caliber ammo can, on strippers – approximately 600 rounds
50 caliber ammo can – 1,440 rounds of original package ammunition


7.62x54R (Moisin Nagant ammo)
Note: I think this would be similar for 30-06 or similar cartridges

30 caliber ammo can, loose – 420 rounds
50 caliber ammo can, loose – approximately 700 rounds (may have to be hand-stacked)
FAT 50 caliber can, loose – approximately 770 or so

30-06 (Specifically)

50 caliber ammo can – 60 (Sixty) M1 Garand en bloc clips (480 rds)

12 Gauge (2 ¾ inch)

30 caliber ammo can, loose – approximately 140 rounds
50 caliber ammo can, loose – approximately 250 rounds? Seems high
50 caliber ammo can – 5 round boxes (think buckshot) – 185 rounds

22 Long Rifle

30 caliber ammo can, loose – approximately 3,300 rounds