[RDGAC]

Interesting point, Zifir. Britain, as I recall, was one of the first nations to establish a system of Pattern Weapons (and other military accoutrements), and even that was by no means universally adhered to; partially that was the consequence of pre-precision engineering solutions being applied to the problem, with all the resulting non-interchangeability of parts one would expect, but partially it was accounted for by the simple demands of wartime exigencies and various military traditions. Nominally, every British infantry soldier should have had a Bess of some pattern or other, all with broadly interchangeable parts, firing much the same ammunition. Even with the advantage of the Pattern system, however, this wasn't guaranteed, and the problem was merely made worse by, for instance, the tendency of officers to purchase their own fusils privately, thus adding non-standard ammunition to the mix.

With that being borne in mind, if we turn our attention to the Ottoman Empire, we surely find that the Ottomans didn't even have the advantage of being at the head of an Empire either sufficiently far-flung (and lacking in a history of indigenous gun-making to quality equivalent to Ottoman products) or ethnically/culturally/technologically uniform (allowing the easy imposition of some form of standardisation of equipment). Instead, the Ottoman Empire encompassed notably fractious regions, each of which had a long history of making guns their own particular, unique way, be that the Albanian rat-tail, the Ottoman tufek or the Bosnian boyliya. Their influence, moreover, spread across regions which also had a very strong tradition of doing things their own way, viz. Algerian and Moroccan guns.

In other words, my suggestion is that the Ottomans didn't have the luxury either of presiding over a relatively homogeneous dominion, wherein their own style of weapon-making was already fairly similar to that of their subjects, or of an Empire sufficiently technologically inferior, or distant, to make standardisation around their design desirable or practical. The Ottomans, instead, had to work with what they had; what they had was a large number of local gunsmiths, in a number of generally restless lands, who would quite happily turn out their products to anyone who'd pay.

Combine this with the general Ottoman tendency to allow their subjects to continue following their own traditions - to an extent - and it seems reasonable to suggest that the Ottoman Empire would, from time to time, order arms from out-of-the-way, local contractors. It might be a question of keeping them busy (for a busy gunsmith is probably less likely to sell his wares to criminals, insurgents etc), or of a sudden upsurge in need for arms making the obtaining of any sort of weapons necessary (in which case, providing they can all use the same ammunition, it might not even matter too much that their designs, or styles, differ); it might also be a question of arming a locally-raised corps with weapons with which they're familiar, both as a sop to wounded pride and as to take advantage of that familiarity.

... sorry, that turned out longer than I expected.