A 20mm anti-tank rifle in ultra slow motion destroying some steel plates.
Anti-tank rifles were very quickly made mostly irrelevent as tank armor increased in thickness. Projectile based anti-tank rifles struggled to penetrate the thicker armor, so anti-tank measures switched over to explosive based, such as rocket launchers, or vehicle based, such as large anti-tank cannons that must be moved around by vehicles or livestock.
The age of the hand held anti-tank gun was very short, but we get some awesome footage from it.
The source part of that image can be found at about 4 min 15 seconds in the following video.