A proper set of snap-caps are the real thing, and should accompany every double rifle! They come in two weights, light ones for EXTRACTORS, and cartridge weight ones for EJECTORS. The aluminium ones are not strong enough for anything. The strickers hitting them will eventually bend the RIMS letting the strickers over extend! This is not good. Barring real proper snap-caps, they can be made from two empty cases. If you have ejectors, fill the case with molten aluminum, then cut the front off back far enough so they weigh the same as a full cartridge case. This will allows the ejectors to toss the snap-cap like the empties, but still be short! The primer pockets are then filled with a pencil errasors. The rubber will take up the strike of the stricker, and rebound to set the striker back into the standing breach. Drop a few extras, in your rifle case, to replace them as they ware! For the 470, the nicol plated cases from FEDERAL cartridge Co. make very nice ones, that look like the commercialy made ones , and cost about $4 USD to make, compared to $50 USD for real ones!

If you don't care how long they are, you can simply put errasors in the primer pockets of two empties, and go from there!