On Zamak guns, it is the frame that will be an alloy. The cylinders and bbls are steel. Any that come out of Germany - including the RGs, Arminius, et al - will have had to pass German proof testing. The frames may crack eventually, and probably will if used heavily, but there ought be relatively little risk of one exploding or anything of that nature.
The Russians and Turks tend to use good quality steel in their guns. The Turks have been making guns longer than just about anybody. Turkey is part of the EU and Nato and isn't a Third World nation. Nor is Russia. Rather than being known for failing, Russian guns are in fact mostly know for being the sort of thing one can fix with a hammer or use as a hammer should the need arise.
A German revolver with a Zamak frame - assuming it is in good condition - the thing to watch for would actually be reliable primer detonation in double action mode and does it spit or shave lead. Many of them seem to go bang best when used as single actions.
In .22 LR - and to some extent .32 SW and .32 SW Long - chamber pressures are low and Zamak guns will last a long time, if not indefinitely.
Some Arminius guns, including their .357, are actually steel frames. These are still imported on and off by EAA.
