The Mayall breechloader is an experimental American breechloading rifle.
The Mayall breechloader was designed by prolific designer and inventor Thomas Jefferson Mayall (died May 1888, aged 60) before the 1880s, in which he actually patented the bolt-action design of his weapon; Mayall is better known for his patent relating to breech loading cannons. A marksmanship competition in September 1882 started by the 2nd Cheshire Volunteers Rifles offered the Mayall as a prize, which suggests that the Mayall actually did enter production. His design has the distinction of being one of the first bolt-action self-contained rifles ever designed.
The Mayall used a patented breechloading design, with a unique bolt-action for its time. The weapon operates like a standard bolt-action rifle, with an extractor but no locking lugs; the bolt itself acts as a locking lug. The hammer would be brought to half-cock, loaded, brought to full-cock and then fired, with the hammer falling on a firing pin which ignited the cartridge.
The Mayall used a self-contained .577 cartridge, known by some as the .577 Mayall. While rather similar to the .577 Snider cartridge, they are non-interchangeable as the .577 Snider was manufactured later.
A carbine variant is known to exist.