Best answer as chosen by user mrsbsss: A SD card is not a MicroSD card.
by R. Proffitt - 7/22/13 6:15 PM
In Reply to: question about micro mem. card for Samsung HMX-W300 by mrsbsss
http://www.samsung.com/us/photography/camcorders/HMX-W300BN/XAA-specs calls out a MicroSD card.
I also spotted a firmware update which you should check out.
The manual at page 26 notes that this memory size is fine. As it's hard to get slower that Class 4 cards if you get the right physical size, it should be fine.