Its a thin line, or a narrow path....
Call it whatever you want, but it is real enough. I'm a former machine gun repairman, and I enjoy discussing autmatic weapons, and how they work. And, yes, all the information is public domain, BUT there is a point where it goes beyond abstract discussion of how a mechanism works and enters into a wonderful gray area that some people think is aiding in the commission of a crime.
Its sad, but as you said, it's the world we live in today. Yes, I can tell you how to make an atom bomb. And yes, you can also look it up for yourself. In general. But if I were to give you specifics, details, dimensions, etc. thenI might be in legal trouble.
Want to talk about why your MG 42 has feed trouble? Fine. Want to understand how the drum magazine of a Lewis gun is different from the drum of a Tommygun? Cool.
Want to know about silencers, so, after getting Fed approval you can make one? Ok, we can do that.
Want to know how to convert a semi auto to full auto? Nope. We don't do that here, because there is no legal way to convert anything anymore.
The Feds have a catch all law, commonly called "conspiracy", that lets them prosecute people who are involved in some fashion, but have not themselves physically commited a certain crime. The mob boss who orders the hit, doesn't pull the trigger himself, but can be jailed for conspiracy. The bomber who doesn't actually blow anything up, but tried to with dummy explosives he thought were real gets nailed with conspiracy.
And the poor well meaning guy who just provides some information (and maybe the web site he does it on) about how to convert a semi auto might just wind up in the same boat. So we try and steer well clear of anything remotely like that.
Is sad, but it's the way things are.
All else being equal (and it almost never is) bigger bullets tend to work better.