...to something like the bomb over Hiroshima, or lower tech designs.
Here's a BBC link with actual instructions for a low tech design:
http://www.bbc.co.uk/dna/h2g2/alabaster/A676352In my own experience this one would take a bit of practice before you could get it to work properly. I think the design would be very fussy, and misfires would make a big mess. You'd want to test it out with some other heavy metal besides U-235 quite a few times just to make sure you were doing it right.
And, to quote from the above article,
"It could be noted at this point that the Hiroshima bomb was only about 2% efficient, 98% of the fissile material was blasted away from the critical mass by the initial nuclear explosion, thus stopping the chain reaction long before it attained its maximum capacity."Modern high efficiency bomb designs do not have that problem, but they are much more difficult to build, which was one reason for all that testing the USA and USSR did.
Furthermore, I'll speculate that there is a lot of very deliberate (and subtle) misinformation out there on the internet, of the sort that would be very dangerous to any amateur atomic bomb builders.
This article from the Bulletin of the Atomic Scientists about apartheid South Africa's nuclear bomb is a pretty good one to give you some idea of what's involved:
http://www.thebulletin.org/article.php?art_ofn=ja94albrightIt's very relevant to current discussions about Iran.
:hi: (Obligatory wave to "Agent Mike.")