Your firearm manual will specify the caliber of ammunition you need to buy. It is also stamped on the barrel of the gun. For any caliber there are many custom variations which will work, and as many that will not work. For handguns, the bullet weight is not critical if given a choice in the manual, so purchase the lighter weight (smaller number after the ‘x’, such as .380 x 90 or .380 x 95, where .380 is the caliber) to start with. You will see other labels, like ACP, Auto, Kurtz, Short, FMJ, JHP, Mag, etc. At this point, ignore those and follow the manual’s suggestion until you become more gun-terminology saavy.
For shotguns, the 20 ga. x 2-3/4″ shell load comes in several shot sizes, weights, and quantities of shot pellets. The smaller the pellet, the higher the number (from 00 to 9). The higher the weight (3/4 oz to 1-1/4 oz) the more the shot. Choose the mid size of what is available to purchase, such as 6 shot, and 7/8 oz. The choices relate more to specific game loads needed for hunting or target, like goose or quail, or skeet and trap. The length of the shell also can differ from 2-5/8″ to 3″, but there is only one your shotgun can take. Avoid Magnum loads.
We do not sell ammunition, but it can be purchased from your local sporting goods stores except for WalMart or Dick’s, and at many local hardware stores. It is popularly purchased at gun shows, gun sales showrooms, and on the internet. If you are unsure of what to purchase, take the instruction manual that came with the firearm along with you, and show it to the clerk behind the counter.