Ten rounds was the standard military capacity. If you have an original or restored rifle, this is what you should have. Most 5-round mags are cut-down military mags, some are commercial production, NONE are correct for the rifle.
The Lee-Enfield Rifle Number 5, generally termed the "Jungle Carbine" generally is seen with the same magazine as the Number 4. They are about $35 right now and they ARE available. There actually IS a proper Number 5 magazine, but these are rarely seen. They look the same as a Number 4 magazine (single rib on the back) but they also have two formed lugs, each about half an inch in height and an eighth of an inch in width, halfway between the bottom of the magazine rib and the bottom of the magazine, one on each side of the central magazine axis, evenly spaced. When the carbine is fitted with the special lightweight triggerguard, this magazine assures proper feeding. So many parts got changed around that these are quite scarce these days. No matter, the Number 4 magazine was approved for the Number 5 and generally accepted as original..... and they are available.
BTW, you only need one magazine for your rifle. They were issed with only one magazine because it is actually much faster to reload the magazine from chargers (mistaenly called "stripper clips") than it is to change magazines. Chargers are available usually for about a buck and are very hady little things to have. If you get a sticky one, you can smooth the feed lips with a bit of Crocus cloth and you're away.
Hope this helps.
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