While they haven’t gotten nearly the coverage as the Syrian military’s “barrel bombs,” makeshift explosives-filled oil barrels rolled out of helicopters, Syrian rebel factions have turned to their own improvised weapons in the ongoing civil war.

Dubbing them “hell cannons,” the Syrian Observatory for Human Rights detailed the problem of rebels making improvised mortars out of old cooking gas containers filled with fertilizer and fired, by cannon, into government-held areas.

The problem is the same as that of the barrel bombs, they’re wildly inaccurate and tend to veer off-course, killing large numbers of civilian bystanders. The observatory confirmed over 300 civilians have been killed with the weapons since July, overwhelmingly in Aleppo.

Reports of hell cannon usage in Syria have been around for years, but this is the first report detailing the civilian consequences of such weaponry, something which has long been ignored.