What is a bull-pup you ask? It is simply a rifle with the grip and trigger assembly moved forward of the breach and magazine well. Operation is just like every other modern gas-operated rifle. It results in a shorter weapon, but not a shorter barrel length, which can degrade long distance accuracy.
And while futuristic appearing to this day, the first generation of bull-pups were birthed in the years right after World War II.
It was the late 1940s when British small arms experts embarked upon a search for the next generation of combat rifles to replace the bolt-action Short Magazine Lee Enfield.
Seeing the success of the German FG-42 semi-bull-pup Fallschirmjager rifle, the British teams (supplemented by a cadre of Polish engineers brought over at the start of the war) began to create a gas-operated rifle and new caliber that would prove worthy but too far ahead of their time and not impervious to political pressure.
Designated the EM-2 the bull-up rifle had a long stroke piston method of operation (where gas was siphoned out of the barrel, operating a piston that cycled the action.) In addition to a detachble box style magazine (with original prototypes being fed by stripper clips,) the EM-2 possessed a glass optic sight as a primary aiming method, with iron sights as back up, unusual for the period.
The caliber EM-2 was chambered in was also distinct for the time as all post-WWII nations were developing "intermediate" calibers for future rifles and machine guns.
The U.S. looked at the .30-06 round (used in Word War I and II,) essentially cutting the overall length of the case to create the 7.62x51mm. The Soviets, looking at the work of German small arms designers and the 7.92 Kurz, developed the 7.62x39 mm cartridge and placed it into the great AK-47. And the British, they too started their own caliber search.
They would champion the .280, or 7x43 mm round, a true intermediate combat caliber, closely matching the 7.62x51mm being developed by the U.S. The rifle the round was ideally suited for was the EM-2. Shorter in length and relatively lighter weight, with select-fire capability, the EM-2 was thought of highly enough to be briefly adopted by the UK.
However, political moves helped cut the legs out of from under the round and rifle as the newly organized NATO threw its multi-national weight behind a U.S. backed 7.62 x 51mm cartridge. The round going on to be chambered in the M-14, Heckler & Koch G-3 and the FN-FAL, a rifle which would be adopted by the British, Canadian and a number of other militaries shortly after.
Redesigning the EM-2 to accommodate the 7.62mm NATO round was considered unfeasible, signaling the death knell for this unusual combat rifle.
It would take nearly 40 years before the British would get their bull-pup, designated the L85A and chambered in the 5.56mm caliber.
Yet armies are going back to the future as combat cases in Afghanistan are showing the limitations of the 5.56mm round in engagements at distance. As a result NATO armies are deploying larger numbers of 7.62mm rifles (including modernized M14s 3x older than the soldiers using them,) as well as commissioning new rifle designs for caliber that killed the British .280.