I've featured the smallest ever revolver and the biggest / most powerful revolver - so now maybe it's time for the worst ever made suggestions:
Colt M1877. . it was offered in three calibres, the .32" "Rainmaker", the .38"Long Colt "Lightning", and the .41""Thunderer" - But sad to say all flavours of the new double action revolver suffered from weak internal components, poor and complicated design and - despite the resounding but unofficial names - all three proved to be so unreliable that they were re-named as "The Gunsmiths' Favourite".
My choice of rubbish rifle is either the Cochran or Porter Turret Rifle of 1851 - a percussion multi-shot that had the unfortunate trick of igniting all its loaded chambers together - with startling results - as there was always one chamber facing rearwards pointing directly at the shooter.
- So when firing the Turret Rifle you needed to keep your hands away from the turret chambers gasses - but your face also needed to be held away from the stock.
Small Note: There are suggestions online that the first military version of the (AR15) M16 rifle (Introduced for use in Vietnam in 1963) would qualify as the worst ever rifle.. This adapted ArmaLite rifle deserves its own story.
"J" suggests that the "worst machine gun"- 'Light Machine Gun' class should be the WW1 USA Mle 1918 30-06 version of the Chauchat that was built in the French Gladiator works (Paris).
Other versions made in different plants seemed to have performed better for the Belgians and French.