That's what I got for the 5.56 on clips. I've been in the basement in my gun room testing capacity for the .30 cans.
Here's some basic figures.
.30 Caliber ammo can - 10" x 3 3/8" x 6 1/2"
5.56
680 on stripper clips
500 on stripper clips in boxes + room for 5-6 single clips of 10
7.62x51
340-350 loose
370 on stripper clips
.30-06
330-340 loose*
370 on stripper clips
280 in enblocs
8mm Mauser
330-340 loose*
370 on stripper clips
280 on stripper clips in bandoleers
7.62x54R
370 on stripper clips*
7.62x39
560 in Wolf 20 rnd boxes + room for 30-40 loose and or stripper clips
303 British
305-310 on stripper clips*
.50 Caliber ammo can - 5 1/2" x 11" x 7"
5.56x45
1200 loose
7.62x39
760 on stripper clips**
7.62x51
600-620 loose*
* = Estimate, I either didn't have that much of that caliber or I didn't want to take it out of that many 20 rnd boxes or load and unload stripper clip.
** Thanks too UnDeadYoda on GlockTalk