It is said that people who own Harley Davidson tend to think ownership means qualified to work on them.
Same thing for gun owners. Not I am not saying that you can’t work on your own guns, but you really need to know what you are doing.
All the time at the range I see failures in AR15s from not installing the stock correctly, fire control group springs in the wrong places. Firearms unable to be zeroed due to improper sights and sight installation. 1911 and revolver triggers get tuned to the point of unreliability.
I have to be honest, I have done this my self. Had the buffer retaining detent pop up and cause the hammer to not hit the firing pin. Had a connector sold to me as “glock brand” cause reliability issues. Broken screws and bolts using improper torque values. The list goes on.
Many modern firearms are simple to work on. However simple to work on does not equal fool proof. Make sure you know what you are doing when you work on your firearms, and if you are not sure, get an experts help.