Freebsd live usb

Hello. I'm going to make freebsd live usb based on FreeBSD-8.3-RELEASE-i386-livefs.iso. The iso is 257 Megabytes, but after i copy its content to usb drive its volume increases to 971 Megabytes. I tried different methods of copying (tar,cp,cpio) but with the same result. Could anyone help?