Anti-tank rifles are specifically designed to penetrate the armor of military vehicles, particularly tanks. Through two World Wars these rifles continued to evolve, and it became a race between developing super strong rifles and engineering armor strong enough to not be fazed by them.
The first attempt at upping the penetrating power resulted in the so-called “reversed bullet.” According to sources, these bullets used the same cartridge and bullet as the regular round, except the bullet was in a “reversed” position and an increased propelling charge was used. From there, came an “armor-piercing” bullet, called the K bullet.
As rifles improved, however, so too did the tanks . . .
Thicker armor became more and more standard on newer models, and the effectiveness of man-carried rifles lessened dramatically.
Here’s a clip of an anti-tank rifle being fired. You can clearly see these weapons are not designed to be portable – or even shot from a shouldered position for that matter!