It looks like you have a partial private key.
If it's 80 characters, the private key is in Wallet Import Format (WIF).
You can use FinderOuter to find missing keys: https://github.com/Coding-Enthusiast/FinderOuter (Free and opensource runs locally, no need to trust anyone)
If my maths is right there should be 64^14 possible values to be brute force. You can also make use of GPUs to brute force those values faster!
I didn't think it was wif format because he mentioned A-F Letters only and isn't wallet import format base58?
If its hexadecimal then standard would be 64 characters
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Right, but good tips
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Not exactly 64, no.
The key itself is 64 but there is a prepended version byte and 4 extra bytes of checksum at the end. This adds 5 x 2 = 10 hex chars. I'm not sure how you get to 80 but I'm trying to figure it out :)
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