For the gun type, all bets are off - it's a _much_
simpler design.
I wonder what kind of yeild you'd get using a .50 diameter bullet against
a 1.00 diameter target. (inches)
The answer is 0. The ISTR that the critical radius for U235 is about 9 cm.
For plutonium, the critical radius is about 5 cm. Plutonium doesn't work
too well in the gun types, so you would tend to get a small but extremely
messy explosion even with a critical assembly.
There are tricks to getting the critical radius down to lower values...
Eric