This improvised shell (using cylinders of gas) are called "artillery of hell", and are a staple of the indiscriminate shelling by Syrian rebels. How much accuracy do you think that they have? Yesterday, in response to advances by Syrian regime troops in Zabadani, Syrian rebels started to shell the hell out of rif Idlib. How come those shells are not as infamous as barrel bombs (which have been used to Western media acclaim) by Lebanese Army against Nahr Al-Barid refugee camp in 2007.
Remember when the White House told us that the Syrian opposition didn't have the technical means to use chemical munitions?