On page 68 of C. Yust’s “Cartridge Collector’s Notebook” there is a diagram of a very interesting-looking cartridge named the “7 x 55mm Broadway Trust Co.” The cartridge is a very unusual design in that the case has holes in it, so it resembles the 76 and 106mm Recoilless rifle cases. Only this cartridge is obviously much smaller.
There is a short papragrph on the page that reads:
“Development was sponsored by Imperial Chemical Industries in 1946. The project engineer was Charles Burney. The chamber void allows a constant high / low propulsion pressure.”
There is also a diagram of the workings of the weapon, which allows gas pressure to escape through these holes in the case. However, this escaping pressure does not appear to unlock the bolt of the weapon. Can anyone give my any more information on how this weapon / cartridge combination works, or any photos of the weapon or cartridges?
I googled “7 x 55mm Broadway Trust Co. Cartridge” and all it came back with that was relevant was the IAA cartridge / journal issues list in PDF form. It says there is an article on this round in issue 251/3. It calls it the “.270 Broadway Trust Company (BTC) Experimental”.