Police have shared an image of a bag of guns that was found by a passer-by on the same street as a primary school.
The holdall was found on Hurst Avenue, Sale at about 14:00 GMT on 20 February, Greater Manchester Police said.
It contained five pistols, a revolver, ammunition and two smoke grenades, all "wrapped for transit", the force said.
St Margeret Ward RC Primary stands at the southern end of the road, though police could not say precisely how far away the bag was discovered.
Appealing for information, Det Insp Lisa Bradley said officers needed to "know where they came from".
She said it was "not clear whether they were intended for use in Trafford or destined for another location".
"This is a substantial recovery and the loss of such will have undoubtedly caused repercussions amongst those criminally involved," she added.