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I'm translating a Russian blog post into English and got stuck with the proverb, "Whatever a Russian does, they end up making the Kalashnikov gun." (Humorously meaning it's hard or even impossible to get past established patterns of doing things)

Are there any similar proverbs in the English language?

I was trying to omit the reference to a particular nationality and think about other ways to get the message across, e.g. use professions or animals. The only idea I managed to come up with was "What can you expect from a hog but a grunt". But it has negative connotations that are not implied by the original.

I'd greatly appreciate if you share your thoughts on this. Thanks in advance!

Another famous aphorism is the following

you can't teach an old dog new tricks.

said to mean that it is very difficult to teach someone new skills or to change someone's habits or character (Cambridge Dictionary)

Usually said of people who set in their ways and are well past their twenties or thirties...

If you are a hammer, everything looks like a nail.

The usual form of this saying is

If all you have is a hammer, everything looks like a nail,

but the above form is used, and might be closer to what you want.

Not meant as a compliment, but neither is the Russian aphorism I suspect, it's a very well-known saying that claims people cannot change who they are.

a leopard can't/doesn't change its spots

something you say that means a person's character, especially if it is bad, will not change, even if they pretend that it will (Cambridge Dictionary)

The Phrase Finder says of its origins

'A leopard cannot change its spots' is found in the Bible, Jeremiah 13:23 (King James Version):

"Can the Ethiopian change his skin, or the leopard his spots? then may ye also do good, that are accustomed to do evil."