Raimey,

If you were able to acquire the above 30 rounds of ammo, you are in business. From the appearance of the boxes, I think it is post- war manufacture and about as modern as you are likely able to find (other than custom loaded). The 5.5 mm Berdan primers were the standard primers, for the time, and even though difficult to find, a small quantity is available to you. Note the admonishment to use .257" bullets, which are smaller than the standard diameter for this cartridge. You have available to you the possibility of finding .261"bullets. If you take special care of them, 30 cases will last you a long time.
Mike