I know you guys are very enthusiastic about your tests...and that is good. We all like to have fun shooting things up.
However, your test proves absolutely nothing. Building blocks are not buttered with mortar and set one on top another when used in construction. They are buttered, set over vertical and horizontal rebar and then FILLED with a pea gravel, sand and cement mixture. Building block walls are solid when constructed correctly for building use and contain a network of wire tied rebar.
If you were to build with blocks and left them hollow...the building wouldn't be very strong. It takes rebar and concrete mix slurry to interlock them and that is where the strength comes into play.
Build yourself a wall to proper building spec, 4 courses at a time to make sure the cavities are all completely full. Be sure to properly use rebar and concrete / aggregate slurry from the top. Mix your block filling medium to a 8-9 inch slump to ensure proper filling...allow it to cure for 21 days...then redo the test.
When you see a proper commercial building done with these blocks you can assume that they are filled and will provide proper cover from most rounds short of 50 BMG.
Cheers
Mac.