A core dump is two projects: find out what's wrong, fix it. You cannot estimate how long it will take to fix a problem until you know what the problem is.
How are you an expert when you consider a core dump to be a reasonable place someone would try to estimate bugfix time from? You can't estimate until you can plan the work, until you can draw a work breakdown structure and show what must be done. Even projects are chartered with a big budget and time estimate based on "this is 3x bigger than something else, so it takes 3x longer and is 3x as expensive", and then broken down into work that all comes together and says "okay, it's only going to be 2.1x as expensive and take 2.3x as long". That initial budget estimate? It comes from a dozen or five dozen or hundreds of prior projects, all with varying times, so you can say, "Stuff of this size and complexity has a low-water mark of like 5, a high-water mark of like 11, and tends to take more like 7.2" and decide how important the project is and thus if you want to budget for more like 5 or more like 11--and the same goes for the broken down work.
You can't even estimate what a bugfix is from a core dump. Someone brings you a core dump and says, "I need a bug fixed." They may as well bring you a blueprint and say, "I need a house built." Until you open the damn blue print up and see if you have a 1200sqft row home or a 4500 sqft Victorian, you have no fucking clue what you're doing, and can't tell them how long it's going to take. Once you unroll the damn thing, you can give them a ballpark estimate by glancing at the paper once; take a few hours to study the blueprints and work out what work actually needs to be done, and you can give them a better estimate.