This is Dragon's 1/144th Karl mortar 60cm (600mm) version.
http://i79.photobucket.com/albums/j160/darrengreenwood/2007models115-1.jpg

http://i79.photobucket.com/albums/j160/darrengreenwood/2007models116-1.jpg

http://i79.photobucket.com/albums/j160/darrengreenwood/2007models117-1.jpg

http://i79.photobucket.com/albums/j160/darrengreenwood/2007models118-1.jpg

http://i79.photobucket.com/albums/j160/darrengreenwood/2007models119-1.jpg

I really like this one. 1/144 scale? That's pretty small. Nice work!