I'm not seeing the expected wear, residual markings/impressions & signs of corrosion in any of the ammo loops that I would have expected to see. I was expecting to see more wear from bullets left in it while on the trail, maybe some green tarnishing from the old brass in a few pockets, etc.. (I see the odd mark here and there, but no deep staining from the lead, nor any noticeable markers inside the pockets themselves) The metal hardware, unless it's silver, should be showing a lot more age and patina as well I think. I'd also have expected to see a bit more "hip sag" showing in the leather from it being worn for a few years.
Also, the uneven heighth of the shell pockets seems out of place. Quality was important back then, and this would not have been something that just anyone could have afforded, so I doubt the leather strip for the pockets would be cut as "sloppily" is it seems to have been done. It does add to the "old timer" look of it though, and such things are usually a hint to reproduction work.
My gut reaction is that it is a reproduction - BUT, a very well done reproduction! Regardless of its authenticity, I'd be damn proud to carry my ammo in it, or even hang it above my mantle.
Very nice find! Since you picked it up at a garage sale, if you paid <$100 I think you did very well indeed. If the cash was available to me, I'd probably have considered as much as $150 just to have it as a wall hanger.