There have been some comments that suggest an answer has been found, but some of these have been deleted, in part, it appears, because some of the claims made in the source are not verifiable. So let us try to put it all together and stick to evidence-based statements.
- A simple internet search gives exactly one result - from the Urban Dictionary
- This meaning fits the context in the original question.
- It makes no claim as to when the term came into use, where it was used, or by whom or anything else of that nature.
- It makes a claim about the origin of the word that is not supported by evidence, and is not sufficiently precise in what it claims to be even testable.
- It does, however, provide a graph of usage. There is no vertical scale or implication of what data set it is based on. The erratic nature of the results (with many blank months) does suggest the phrase is not common.
Terms for this sort of thing are numerous and many of them are ephemeral. A few internet searches will produce literally hundreds. This means, as the question shows, that any such term runs the risk of not being understood, particularly after the passage of time, in a different place, or amongst people who are not part of the same scene.
Having found poor evidence for one possible meaning, we have to consider if it is right. All we have to go on is that there is evidence for this meaning, albeit not very satisfactory. Other obvious possibilities are that it is a reference to something (perhaps a drug) being sold at 40% strength, but there is no evidence for this, and it does not fit the context as well. (As it happens, whiskey is usually 40% alcohol and labelled as such in Europe. This does not make sense in the context and I believe this terminology is not used in America.)
As for the best translation, I am sure there are lots available, but the problem is to find something that sounds sufficiently jargony, without the risk that it won't be understood by many people.