Simply go to youtube and there are HUNDRED of video's on how to make a firearm of one type or another.
Don't believe me?
Click : Home made gun
To say nothing of the hundreds of thousands of web pages on how to make your own firearm.
Click Home Made Gun Google
What about all the videos and pages on youtube and google about how to make explosives?
Isn't it obvius to you anti-gunners. You cannot UNMAKE technology.