BY and large, the use of Factory pre-linked or pre-belted MG ammo in rifle/heavy calibres is a Wartime contingency.
nearly all national armies had on issue “belt filling machines”, initially for cloth/canvass belts (as for Maxims, Vickers, and brownings etc) and in WWII, link filling machines, of much more simple construction, were also available.
Many countries, however, continued the practice of supplying from the factory ammo in either clips for rifle use, or Loose pack/bundles/large boxes(50s or 100s), for the Local ordnance depot to “belt up” according to need.
The use of magazine-fed Light machine guns also required the use of NON clipped, but large packs of ammo.
Countries which used Strip-fed Hotchkiss type guns had their ammo pre-packed at the factory, and wrapped in paper (French) or in carboard re-enforced sleeve boxes(Japan).
With the onset of WWI and WW II, the large expenditure of all types of ammo caused the supply services to “push back” the filling of Link belts to the Factories, in the case of Infantry use, and by an large, the USA utilised pre-packing for both Air and Land services, especially by the end of WW II.
The RAF and RAAF got in large quantites of ball ammo factory pre-linked, some with 1 in 5 tracer, and added other types of special cartridges as required by hand at the airfield or base.
RAF and RAAF .50 BMG came already pre-linked from the factory, and “aircraft load” belts were assembled as required by the Ground crew armourers at the bases.
The European nations of both sides continued with loading belts as required, the but German war effort did go to pre-filled Belts by the time of the Russian campaign.
The Russians, on the other hand, still handfilled their belts and links right throughout the war, as evidenced by cans of 12,7 and 20mm ammo packed loose in spamcans.
The use of individual disposable metal links made for the “use it and throw it away” mentality, leading to Pre-filling in a factory environment, whilst the European belts, in the main, were flexible metal held togethewr in units of 50 or 100 by inter-link spiral wire connectors…meaning that the belt was not to be thrown away, but refilled when time allowed.
The British still used cotton wover “stripless” belts for Vickers in WW II, but these were considered “expendable”, and since Vickers ammo came prepacked in 250 round belts, there was no need to “refill” as there had been in WW I with the expensive Cotton and Brass strip" Maxim" type belt.
I remember in my days in Mounted Infantry (1972-74) “filling” Browning cloth belts with ammo from US 1943-44 boxes (20 rounders) with a mixture of Ball, AP and FN Tracer ammo.–the FN ammo came in 100 round boxes.
Not a link to be seen then…but by the time more recent (Post Vietnam) .30 cal ammo became available, it was all “Factory Linked” in “Functional Lots” already containing Tracer and AP. (usu. just Tracer. and Ball).
Of course, after 1942, all US ammo belting was considered" expense stores" and not expected to be returned or re-filled. The uses of BMG cloth belts are numerous ( Rifle slings, arm slings, Shell dressing bandages, tourniquets, tying up prisoners, the list goes on.)
Nowadays (2007) all small arms ammo supplied as “Combat ready” is either in Stripper or packet clips ready for large capacity magazines, or already belted up with or without the necessary tracer fraction. And it is all
factory" done. This at l;east is true for almost all Western nations…the ex-Soviet Block still has some “Bulk or Loose” pack ammo supplied, but tactical considerations have forced the use of Factory filled belts to be issued.
As to the use of readily accessible ammo cases, that problem has been around since the Battle of Isandlwana (1879) and the problems opening screwd down and soldered containers of .450MH ammo.
By WWI, ammo was delivered to the front in Boxes with sliding Lids, or hinged and latched lids, where simple tools(Bayonet, clasp knife) could open the outer wooden box, and a soldered “rip top” seal could open the inner tinplate liner. The French and Germans went one better, using a thin zinc metal Liner which could be ripped open by the piano-wire ripper set in place, or simply by using a bayonet. The cases were closed by a leather strap and buckle, a simple “fold over” latch.
Only the Russians/Soviets continued right to the present day with “Spam cans” of thick sheeting, and supplied with a hefty can opener, or the Chinese improvement : a “sardine can” type key, which wound up a strip of side wall, specially scored to weaken it, so the can could be opened more quickly.
The Germans used a “Combat can” specially engineered so the carrying handles were offset, and thus it was easy to carry two such cans in one handgrip. But these cans were also of heavy sheet steel, and more for use with MGs(initially, Maxim, then MG34 and 42.) The common infantryman still got his ammo in 15 round , 3 clip packets (just right to fit his ammo pouches)
As to whether it is a bit of a stretch for this forum, the collection of Cartridges also includes the packets, links, and larger containers they were delivered in, whether they were “permanent” type containers(steel or purpose built wood) or “Disposable” such as zinc tins, plywood outers, simple crates, etc. Sometimes it is only the label on the packet or box which identifies the contents, with regardas to type, manufacturers, lot number etc ( see the Soviet ammo, and of course, Japanese Ammo (which notoriously had not headstamps (except IJN).
IN the heat of battle, all ammo containers become “dispensable”, from the paper wrappers(Eastern Bloc ammo ) being used for sanitary purposes, to the crates being filled with soil to form protection from shellfire, etc, and other items (bandoleers, belts, etc,) being used for a host of non-ammo tasks. German “PatronenKasten” of pressed cardboard, were often used to kindle small fires for that warmed the “Ersatz” coffee in the trenches or the icy ground of the Russian Steppes.