Why is it fine for shotgun shells to be made of plastic but polymer casings for rifle cartridges are considered “unreliable” or “bad” ?

Question

I’ve never fired/handled guns but have some knowledge of guns and their basic mechanisms, and this thought just came across. If you could make cartridges out of polymer/plastic, and they are significantly lighter, wouldn’t you want to switch to them asap? yet there is no adoption. On the other hand shotgun shells have always been plastic but it’s not problematic in any way? why is this the case?

In: 24

Answer 1

It has to do with the amount of propellant used and the resulting chamber pressure. Rifle cartridges can see 50,000 psi chamber pressure, which necessitates a metallic case. Shotguns use much less propellant, so the chamber pressures are 10-15,000 psi, so a plastic case can be used. Note that the head of the shotgun shell is still made of metal