Gold and silver values are tied to manufacturing. If SHTF, there won't be any manufacturing.
Can't eat metal, nobody needs it to survive. Nobody will want it for any good reason, i.e. only as a habit of thought: "I want it". Want is different than need.
That being said, I bought silver in the 90's on every payday at 3.5 times face. Today it is probably 25 times face. I think 10% of your portfolio is a good number. I would buy farm land before silver or gold. Food is everything.
In 1964, when silver coins ended, a one pound loaf of white bread was 10 cents. Today, a silver dime is @ $2.50, as is a one pound loaf of white bread. The buying power is about the same, so silver doesn't go up, but it is steady.
I bought silver after reading of the German depression and inflation. With hyperinflation comes government price freezes, say 10 cents on a loaf. The baker has to pay inflated prices for grain on the underground market and can't afford to sell for 10 cents. With penalties up to death, they won't take $1 for the loaf, but since coinage is recognized as face value, the 10 cent silver coin can be used with a metal value at $1.
The baker gets his $1, the buyer pays only 10 cents as allowed by law, and eats for a day.
I buy mostly Mercury Head Dimes as everybody knows they are Silver (90%) and they aren't worth enough to counterfeit, unlike the fake silver dollars out there that fool even experienced buyers. So beware.