A piezo based fuse in the nose is an easy way to construct the fuse. It's also easy to construct a safety for it: stick a cap to protect the piezo from getting

A piezo based fuse in the nose is an easy way to construct the fuse. It's also easy to construct a safety for it: stick a cap to protect the piezo from getting hit. That said, the safety cap doesn't help if you accidentally trip and fall after taking the cap off. Most western single use AT designs use a different safety that deactivates on firing.