Dear Auntie Gun Nut,
Okay, I understand the sight thing, but what about these bolt handles on my old rifles? Why are some bent and some straight? Also, some of my rifles are really, really long, and others are just tiny. Could people in fin de last siecle Europe just not make up their minds, or what?
During the Golden Age of the military bolt action rifle, it was common to issue long rifles to infantrymen that were optimized for long sight radius, long-range ballistics, and (probably most important to the general staffs of the time) bayonet fighting. These unwieldy looking smokepoles usually had straight bolt handles for positive operation under all conditions. Very short carbines were issued to engineers, cannon cockers, mountain troops, bicycle troops, and cavalry, who needed a more compact arm that could be kept slung while leaving both hands free to do their primary jobs, like building bridges, cocking cannon or climbing mountains. These carbines often had bent bolt handles, to prevent their snagging on things while the troopies went about their chores. Incidentally, most artillery and engineer carbines had their sling swivels mounted on the bottom, in the same position as an infantry rifle's, while those on cavalry carbines tended to be mounted along the side of the weapon opposite the bolt handle, allowing it to be slung diagonally across the cavalry trooper's back; a much more secure method of toting the carbine about while sitting on the back of a galloping horse, waving sabers, pistols, and lances around.
It was the British who first introduced a General Purpose rifle for army-wide issue, in the shape of the "Short, Magazine, Lee-Enfield", or SMLE (which is, as wags are fond of pointing out, only "Short" when compared to a Long Lee.) This combined the snag-resistant bent bolt of a carbine and a slightly reduced overall length with an arm still equipped with volley sights and of a length suitable for bayonet work. Hot on its heels came the US Model 1903, followed later by the German Kar.98k and the Japanese Type 99 Arisaka.
As the bolt-action faded from the scene, armies generally stayed with one length of rifle, preferring to equip specialist troops with machine pistols. Now, however, in the early 21st Century, one can see echoes of earlier times in the M16/M4 combination used by the US Army, or the AK74/AKS74U (although neither pair has a straight bolt handle...)