This is either a horrible series of typos, or you know nothing about H. 2-6mg of pure diamorphine (heroin) is in the therapeutic dose range for control of severe pain in opiate naive individuals. It's definitely
not an overdose. Refer to the BNF:
Strong recreational doses are in the 15-60mg range, depending on size and tolerance:
It's also important to be clear that street heroin comes in different forms with wildly varying purity and different preparation requirements. The procedure you describe applies only to the least common "china white" form which comes as a salt and is readily soluble in water (and frequently contains some amount of fent these days).
Depending on location "black tar" and "brown" (freebase) are more common. Brown is the norm in Europe and black tar is common in parts of the US and the Americas. These require different handling and in the case of freebase, an acid (citric, ascorbic etc.) in order to dissolve in water.
Black tar is a crude mixture of incompletely acetylated products (3-MAM and 6-MAM as well as the desired diacetylmorphine) and is basically nasty and very hard on the body. All forms are frequently cut - sometimes very heavily - so it's almost impossible to guage an accurate dose unless you're familiar with the product at hand.
The hand is usually a site of last resort for long term users who have collapsed the more accessible and less painful sites. Don't try this at home.
I'm not going to provide more details - directions can be readily found for the curious, including lots of information on safer consumption practices, but your advice is way off base on this.
Where are you getting this? On the street it's typically sold in small "wraps" or bags, often 1/10th of a gram (a "ten bag", sometimes "nickel bag or "dime bag" with varying quantities depending on region).