There's no big hollowpoint, polymer tip, or exposed lead to start them off expanding reliably. So they can pencil through stuff.
The jackets are pretty thin too. So if they do start to expand, they can pretty much explode. With no solid base or bonding to hold any of it together to help something punch through.
Or if you're lucky, they can behave like a berger and perform beautifully.
Problem is you have no way of knowing which of those outcomes you're gonna get.
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