Lawyers may not know much about guns but they do know a lot about the court system. Its worth listening to what they have to say.
We all like to think that if we have to use a gun it will be so clearly be a case of self defense that it will never go to court. But the criminals get to decide the specific conditions, not us. Its not always clear cut.
Suppose a group of unarmed but large, strong and aggressive young teenagers tries to intimidate you into giving them your wallet and won't take no for an answer. Don't shoot and you could end up getting robbed, beaten to within an inch of your life or killed. Shoot and the media will give plenty of air time to the grieving mothers talking about how the crazy gun nut needlessly gunned down their little angels that never hurt a fly.
If it does go to court a jury of your peers will not mean 12 people that go shooting weekly and spend their spare time reading gun forums. It means 12 random people that likely know even less about guns than the attorneys you mentioned. A prosecutor could succesfully try to convince them that someone who "makes homemade bullets" is someone that was looking for a fight.