I don't think you can achieve dangerous pressure because you can't get much weight from shot. .22LR shot doesn't generate enough recoil
impulse to operate the slide on a .22 auto without modifications to the firearm.
Yes, the capsules are fragile. Crinkle-crimped aluminum cases are probably the best bet but that doesn't leave enough room for goose loads. CCI loads most of their shot in aluminum cases and STILL use plastic capsules.
I've been trying to acquire .22LR crinkle-crimp brass cased shot loads for rattlers on prairie dog shoots for quite a while with no luck.
The plastic CCI loads work great but are fragile. Centerfire loads can be carried in belt loops for protection to the plastic if you don't mind 'going cowboy.'
Advantage - S&W Kit gun with speed loaders if you wander into a Kansas snake den.
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