“The cartridge was named after a German Anti-Tank gun designer. Gerlach was the first man, prior to World War II, to break 4,000FPS with anti-tank cannon. He used a tapered bore. In his 28-20, the projectile was 28mm in diameter at the breech and exited the muzzle at 20mm diameter. This change in diameter was allowed by collapsible skits on the projectile which folded in as it moved down the tapered bore.”
From the A-Square manual

Also noted as far as loads go they have it with 146gr of H-4895 out of a 34 inch barrel going 5,325 fps with a 118gr Monolithic Solid…………………yea….

there is a tid bit for ya!
pretty nuts huh?

Pat