Remember kids, don’t try this at home — or do. If you have a bulletproof helmet that needs testing, then go for it. I won’t stop you. I’m not your real dad.
This ain’t Sesame Street; we’re adults here. If you want to shoot your friend in the head, that’s your business. Just make sure that your friend doesn’t mind being shot in the face and you should be fine. It’s especially helpful if he doesn’t die immediately after being shot in the head, because that would make it slightly illegal in some places. I don’t know what the laws are like in Russia, so he might get a pass, but if you’re in the US of A be very careful when shooting your friends in the face.
I won’t tell you what to do, but I do advise taking some cautionary measures. Make sure that the bulletproof helmet is actually bulletproof before testing it on yourself. While that might take some of the fun out of the testing process, it will significantly improve your chance of living long enough to see your helmet go into production. Also, make sure that your friend knows what he’s shooting at. If you’re testing a helmet one day and body armor the next, make sure you get everything straightened out beforehand. Nothing ruins a bulletproof helmet test like being shot in the stomach.