3.7 inch AA expanded cartridge case mystery

[charley777]

Greetings to all
Have just found this 3.7 inch AA case.
It has reasonable condition base stencil.
Two questions ...
Who is the maker DB/C ?
And what has caused the drastic swelling in the upper half of the case?
Is it some kind of "trench art" ?
Thanks very much

 

[ron3350]

It is Canadian by Dominion Bridge Co, Toronto.

 

[hangarman]

looks like the primer has been soldered in so could well be trench art. Have seen .303 fired in a .410 chamber that has priduced similar effects. The neck and shoulders expand until the projectile is ejected from the cartridge and then stop expanding because there is no longer any back pressure.