The Bren Ten is an interesting story of handgun development and business failure. The gun was first developed by Dornaus & Dixon, with the consulting help of the iconic Col. Jeff Cooper. It was intended to be a handgun to improve upon the venerable 1911 in every way.
To satisfy the adherents to the theory of large-caliber handgun cartridges, the gun was designed around a new 10mm cartridge designed by Norma. This cartridge would propel a 200 grain bullet at 1200 fps from a 5 inch barrel, making it the most powerful service handgun cartridge in production. It would use a 10-round magazine, and also be convertible to .45ACP.
The gun itself was based on the excellent Czech CZ-75 (made at Brno, which is where the "Bren" portion of the pistol's name came from). It had full length slide rails, a DA/SA trigger that could be carried cocked and locked, and nice big sights.
Unfortunately, a combination of production quality problems, inadequate magazine design, preorders, and other issues led to the company quickly falling into tough financial straights. The guns were only manufactured for about 2 years before bankruptcy ended production. Some had been shipped without magazines, and Bren Ten magazines remain a sought-after commodity today.