In the short term, OP, whats his profile like? Does he like loud/quiet, touch/no touching, light/dark, etc? I'm sure those of us with experience of ASD could suggest some things that might help calm him. One of my DC likes deep pressure and weight so if he's headed for a blow up then wrapping him in a weighted blanket can soothe him until it passes. My other autistic DC avoids touch, hates wearing clothes even, but loves water so often of he's on the path to melting down then a bath helps soothe him.
Keep a diary of incidents - specifically note down what happened, what was happening immediately before, how he was acting/how he reacted, and what happened after the incident. It will help you to look for patterns and triggers which can help with pre-empting the outbursts in future. Younger DC becomes "stalky" when he is reaching breaking point, pacing around like a lion in a cage, so I know if he starts the stiff, pacing movements then he needs intervention. Older DC becomes almost maniacal in being silly then will suddenly turn violent so I know when his silliness starts escalating that he needs intervention.
I really recommend PECS cards and to also look at makaton to aid his communication. There are other communication aids too. A company called Chewigem sells a wristband with a red side and a green side that the child can flip over to show if they need some help/support or if they're okay. They also have visual scheduling tools where you put little pictures on a chart to show what is happening now, what is happening next, and what it happening later to help with transitions and expectations.
There's a book called The Explosive Child that explores the behaviour of children prone to violent and aggressive outbursts, I found it really helpful and it was very useful for aiding me in reframing my approach to such behaviour.
If you're not claiming it already then make a claim for DLA, the money can be used towards any aids and adaptations he needs, private respite, to boost family funds if his care is affectig your earnings, etc, whatever is needed in order to best support and care for him.