I actually think your best bet OP is to be completely honest with him when he is calm. 'If you tell children when you're angry that you're going to shoot them then they are not going to want to be friends with you'. Then perhaps try role playing with him what he could do instead.
There a good chance that he won't realise the impact of his words on others and he needs someone to be very clear about the consequences and practice with him what he could do/say instead. Don't expect instant results of course, and there might be quite a long time of him knowing what he should do but not being able to do it when he gets angry.
I often found I needed to be very blunt with DS for him to understand. He also loved slapstick, after he went to the circus and watched the clowns he then thought tripping other kids up and watching them go flying was a really fun game. Getting cross and telling him it was really not a nice thing to do and not to do it again didn't cut it. I had to talk about how someone could get really hurt, have to go to hospital and if they hit their head on the tarmac they could even die and it would be his fault. I had to be very clear and quite blunt about it to have an impact.
Do you get much chance to spend time playing with him? Modelling how to play might really help him. That could be playing with a train set, playing chase, playing football. It could really help him for you to be clear about the 'rules' of play and make sure he is aware of them as he probably isn't, again being very blunt and point out the obvious. The amount of things that I thought were blatantly obvious and DS had no idea about was quite astounding. Perhaps sometimes play his way, however strange his game or rules are and sometimes play 'your' game where there are rules that other children would expect to play by.
If he is going to have a friend round at any point then I would suggest having structured activities for them to do together with you joining in with them as well. DS always found one to one play much easier than trying to fit in with a group. Don't worry about him not having the same freedom as other kids, just see it as him needing more support.
I would also be open about him being autistic. Right now he is potentially being labelled as aggressive, mean, strange and who knows what else, knowing he is autistic is more likely to be a positive IME, people then understand he has a diagnosis rather than giving him their own labels.
I would also say, whatever he is into, lean into it. If he loves My Little Pony or Road signs or whatever else then make the most of it and get books, toys, print off pictures, colour in pictures or make biscuits with him in the shape of whatever he loves. Take advantage of it - I used to be able to get DS out for a walk by suggesting we could talk about Thomas the Tank Engine on the way. He had a TTTE toy for the car and TTTE audio books to help him with car journeys,
The other thing is DS really benefitted from a lot of time to decompress. After school he needed drink, snacks and story and then time on his own to decompress. Does yours have his own room? That is something that is likely to be really important and helpful to him. DS would have really struggled with 3 siblings and is very glad to be an only child.
I agree with possible dyspraxia if he bumps into things a lot, especially if he also struggles with using a knife and fork, riding a bike, hand writing or any other coordination issues.
Goodluck OP! You sound like a great mum, just keep working on it and things will get easier as he gets older and gets better at handling his emotions. Enjoy his quirkiness!