Regarding your friend, you are risking a lot. I also have similar experience to yours, but I was able to feel smaller doses too, and I liked it, but it is not for someone who wants a real opioid high.
About risk, I recommended a guy 100 mg for heavy depression, and I said if it doesn't work take three. 2 were too much for him. You can hardly find someone so high after injecting H. And he was like that for almost a day (No that were not SR tablets.). So, 50 mg were pretty high for him. Ok this one wasn't really big, but a sporty and fit yes. He is not taking them any more. Took them only few times after that crazy first time, and he says it helped him a lot.