Try this:
Spaghetti Western style arterial red- It also washes out of clothes easily and can be eaten reasonably safely (although why you’d want to eat it is beyond me).
Take a teaspoon or two of Arrowroot (a white powder used in baking that you can easily find in health food shops) and add to water heated on the stove. Stir continuously until the mixture becomes gloopy. Add a small amount of red children’s non-toxic powder paint and stir in. The mixture should now be bright red. Add a tiny amount of brown powder paint or coffee concentrate (make this by adding a small amount of water to coffee granules) to darken the blood as required. Store in a bottle or jam jar and thin by adding water to make the blood the required consistency as and when you need it. For bullet hits you need to thin the blood quite a bit to allow it to spray out.
I found this on the internet. I like the ‘Spaghetti Western’ reference. The blood in those movies looks cool, unlike the corn syrup variety.