The grill size tanks are easily penetrated with .223rem. I've noticed that using standard lead core US made FMJ that one hit they just leak out propane (in a neat white low laying mist) but do not ignite. HOWEVER... Using foreign made bi-metal jacketed rounds will spark and ignite the gas instantly.
I cannot say about how much stonger the 100gal plus tanks are then the standard BBQ tanks. But the difference is most likely substantial.
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