I want to store my bitcoin offline, and I want to engrave my 256 bit number (master private key) on metal, and not ever have to use 24 words.
If you want to engrave text on metal, I can advise you on this topic -
Securing Your Seed Phrase with Washers to get acquainted with one of the options for saving text on metal. I understand that you are planning to store master key, in principle you can also do this using washers.
I know this is riskier (if I record one of the numbers wrong I couldn't recover my bitcoin),
Therefore, I can recommend that you make 2-3 copies in order to avoid mistakes and loss of access to your key.
but I'm not worried about that and I want to go ahead with my plan.
This is commendable and I am sure, with a similar attitude and thanks to the advice of bitcointalk forum participants, you will succeed.