Question: What was the calibre of the controversial rifle invented by Sir Charles Henry Augustus Frederick Lockhart Ross?

Context articles: Henry Augustus Smyth
Carabine à tige
Ross rifle
Mitrailleuse
The Wrekin by-election, 1920 (February)
Charles Allom
.280 Ross
Sir Charles Ross, 9th Baronet
Augustus d'Este
The History of Sir Charles Grandison

General Sir Henry Augustus Smyth (1825–1906) was a senior British Army officer.
 He was the son of Admiral William Henry Smyth and the brother of astronomer Charles Piazzi Smyth and geologist Sir Warington Wilkinson Smyth.
 Of his sisters, Henrietta married the theologian Baden Powell and Georgiana the anatomist Sir William Henry Flower.
The carabine à tige (sometimes called a "stem rifle") was a type of black-powder, muzzle-loading rifle invented by Louis-Etienne de Thouvenin.
 The method was an improvement of the invention of another Frenchman, Henri-Gustave Delvigne.
 Delvigne had developed chambered carbines and rampart rifle-muskets so that when forced against the chamber rim by ramming (with three strokes of a heavy ram), the bullet would become deformed and flatten, so as to expand in diameter against the inside of the bore, allowing the bullet to press against the rifling grooves.
 When fired, the bullet accompanied the rifling and spun.
 This was an early attempt to work around one of the greatest hindrances to the use of military rifles; in order for a rifle to impart the proper spin to a projectile, the projectile must fit snugly inside the barrel to engage the rifling grooves.
 However, with the universally-used black powder of the day, weapons would quickly build up a thick layer of fouling when fired.
 After only three or four shot, a typical rifle would be impossible to load without using a mallet to force the bullet down the fouled barrel.
 Designing a projectile that was smaller than the bore of the barrel, to allow easy loading, but which could then be expanded to fit snugly into the bore before firing would allow for the accuracy of rifles, but without the very slow and painstaking reloading procedure necessitated by the heavy fouling.
The Ross rifle was a straight-pull bolt action .303 inch-calibre rifle produced in Canada from 1903 until 1918.
A mitrailleuse (] ; from French "mitraille", "grapeshot") is a type of volley gun with multiple barrels of rifle calibre that can fire either multiple rounds at once or several rounds in rapid succession.
 The earliest true mitrailleuse was invented in 1851 by Belgian Army Captain Fafschamps, 10 years before the advent of the Gatling gun.
 It was followed by the Belgian Montigny mitrailleuse in 1863.
 Then the French 25 barrel ""Canon à Balles"", better known as the Reffye "mitrailleuse", was adopted in great secrecy in 1866.
 It became the first rapid-firing weapon deployed as standard equipment by any army in a major conflict when it was used during the Franco-Prussian War of 1870–71.
 A steel block containing twenty-five 13 mm (.51 calibre) centre-fire cartridges was locked against the breech before firing.
 With the rotation of a crank, the 25 rounds were discharged in rapid succession.
 The sustainable firing rate of the Reffye mitrailleuse was 100 rounds per minute.
 The maximum effective range of the Reffye "mitrailleuse" was about 2000 yards; a distance which placed their batteries beyond the reach of Prussian Dreyse needle rifle fire.
 Reffye mitrailleuses were deployed in six gun batteries and were manned by artillery personnel.
 They were not infantry support weapons but rather a form of special artillery.
The Wrekin by-election of 1920 was held on 7 February 1920.
 The by-election was held due to the death of the incumbent Coalition Liberal MP, Sir Charles Henry Bt.
 It was won by the Independent Conservative candidate Charles Frederick Palmer, who was backed by Horatio Bottomley's Independent Parliamentary Group.
Sir Charles Carrick Allom (1865–1947), grandson of architect Thomas Allom and painter Thomas Carrick, was an eminent English decorator, trained as an architect and knighted for his work on Buckingham Palace.
 Among his American clients in the years preceding World War I was Henry Clay Frick, for whom Allom furnished houses in cooperation with Sir Joseph Duveen, the eminent paintings dealer.
 Allom furnished the Henry Clay Frick House at 71st Street and Fifth Avenue that today houses the Frick Collection, and the neo-Georgian house, "Clayton", in Roslyn, Long Island, designed by Ogden Codman, Jr., that was bought for Frick's daughter-in-law.
 For the grand rooms of parade in Frick's New York house, Sir Charles, whose London workshops produced the plasterwork and "boiseries", kept the furnishings muted, not to compete with Frick's collection of paintings.
 In 1925, when William Randolph Hearst purchased a real castle, St. Donat's in Wales, his choice to furnish it naturally fell upon Sir Charles.
The .280 Ross, also known as the .280 Nitro, .280 Rimless Nitro Express Ross (CIP) and .280 Rimless cartridge, is an approximately 7mm bullet diameter rifle round developed in Canada by F.W. Jones as a consultant to Sir Charles Ross, 9th Baronet, and his Ross Rifle Company of Quebec, Canada for use as a Canadian military cartridge as a replacement for the .303 British, and in a civilianised and sporterised version of his controversial Mark II and Mk III Ross rifle, and first commercially produced by Eley Brothers of London, England, in late 1907.
Sir Charles Henry Augustus Frederick Lockhart Ross, 9th Baronet (4 April 1872 – 29 June 1942) was a Scottish inventor and commercial entrepreneur who invented the innovative and often controversial straight-pull actioned Ross rifle.
Sir Augustus Frederick d'Este, (13 January 1794 – 28 December 1848) was the son of Prince Augustus Frederick, Duke of Sussex, and Lady Augusta Murray, and a grandson of King George III.
 His parents were secretly married on 4 April 1793, in a Church of England ceremony in the Hotel Sarmiento, Rome, and later married again on 5 December 1793 at St George's, Hanover Square, Westminster, using their correct names but without revealing their identities.
 Both marriages were in defiance of the Royal Marriages Act 1772 and were thus legally null and void, at least in English law.
 After the birth of their first child, the marriage was discovered by the King and formally annulled, making their son illegitimate in Great Britain.
The History of Sir Charles Grandison, commonly called "Sir Charles Grandison", is an epistolary novel by English writer Samuel Richardson first published in February 1753.
 The book was a response to Henry Fielding's "The History of Tom Jones, a Foundling", which parodied the morals presented in Richardson's previous novels.
 The novel follows the story of Harriet Byron who is pursued by Sir Hargrave Pollexfen.
 After she rejects Pollexfen, he kidnaps her, and she is only freed when Sir Charles Grandison comes to her rescue.
 After his appearance, the novel focuses on his history and life, and he becomes its central figure.