The biggest thing here is getting used the mini-game that appears when you take apart and assemble some pieces of a gun. The line will move quickly around a circle and you have to left click when the line is inside of the red zone of the circle to accelerate the pieces.
Note: This achievement is not time-based. So if you need to be patient and be ready for every action you do to be ready for the mini-game. The mini-games will never change what pieces they occur on either, so you can remember which pieces activate the sequence.
Here is a video of me getting 100% acceleration with the AK-47 so you can see what it looks like. After you do it a few times, 75% isn't a very hard goal to reach.
If you have issues with the AK-47 (which I did at first), wait and buy the Colt 1911. It has less pieces and the disassembly/assembly seemed way more intuitive atleast for me.