Most military brass made by Winchester is stamped WCC. I believe it stands for Winchester Cartridge Company, but you can ask around at the Winchester collector's site.
As far as special care, if you look at the history of the Springfield 1903 rifles, you find that they had a number of spontaneous receiver disintegrations in the early years. This is usually put off to low serial number receivers which were tempered by the old color tempering method, but in fact General Hatcher found that a portion of the failures could be traced to weak cartridge cases.
Ever since then, the military has been careful to make thick, hard case heads and webs. This means military cases generally have less powder capacity than commercial equivalents and you have to reduce the loads developed in commercial cases to use them. Particularly loads developed in commercial Winchester brass, which often has the lowest brass weight and therefore the greatest powder capacity in a particular chambering.
In .308 I found most LC and most IMI (Israeli Military Industries) cases need about 10% less powder to get to the same pressures as commercial brass. This means they are a little more limited in peak velocity produced, but not enough to matter until you try to shoot much beyond 700 yards. The Remington 30-06 cases I bought actually have the same capacity as my LC 30-06, but commercial Winchester brass has more. I can load about two grains more Varget behind the 175 grain Sierra MK in Winchester 30-06 brass than in LC or Remington cases.
I have only ever shot Winchester commercial brass in my mouse gun, so I haven't got any specific information on military .223 cases, but expect it will be the same story. Less powder. In any event, you always want to back an established rifle load off 10% when you exchange any component for a similar one, no matter how close a match it seems to be. More if it is markedly dissimilar; a less dense bullet of the same weight, for example. Then you must work the load back up incrementally, watching for pressure signs.
Because much rifle powder loading density is almost equal to the density of water, the water overflow capacity of a case has become a common and convenient measure used to compare cases. You take the case and plug the primer pocket with wax or clay. Weigh it on your powder scale to get a tare weight. Then use an eyedropper to fill it just level with the case mouth (do not actually overflow it or you will not only have water to clean up before you can get the right weight, but surface tension will form a meniscus of extra water above the case mouth level that fools the reading). Subtract the tare weight and you have the water capacity of the case in grains.
Since water at room temperature is very close to 1 gram per cubic centimeter (actually .9977224 grams/cc at 72°F), it is a useful standard for cc's or other volumetric comparisons. Just divide the water weight in grains at 72°F by 252.3 to get cubic inches, or multiply cubic inches by 252.3 to get grains of water capacity. Cubic inches make a useful number because most of us own inch calipers. Since you have to subtract the volume of a seated bullet from case capacity to get the remaining volume for powder, you will probably measure the bullet and its seating depth with those inch calipers to figure that volume out. You can take the cubic inches of a seated bullet and multiply by 252.3 and subtract the result from the case water capacity in grains to know how many grains of water capacity remain for powder. This will typically be 5-10% more than the powder capacity, depending what powder you are using?
To get an exact figure, dry out the same case used to determine water capacity and fill it level with the powder you are interested in using. Weigh the powder and divide the result by the water capacity of the case in grains. This will give you a multiplier number (usually 0.9something) which you can multiply the remaining (after bullet seating) water capacity by to get the total powder weight capacity in grains. This number is unrelated to what a safe charge of that powder may be, but we always love to know these things.
Nick
