Why do you need a screw in choke for the newer style shot such as steel when almost all shot shells have a plastic cup around th

[dogface1]

Why do you need a screw in choke for the newer style shot such as steel when almost all shot shells have a plastic cup around the shot anyway?

[Kody]

I understand your thinking in this regard as you assume the plastic wade will protect the barrel or its choke. I believe the issue here is that the steel shot will not compress like a softer lead load as it meets the narrowing of the barrel that is outfitted with a full choke. In effect, you are trying to squeeze a load thru a restriction and steel is not going to cooperate. Pressures likely soar with this partial obstruction and you are entering a danger zone. That is the reason for a modified choke with the use of steel.
It is also the reason the Canada Geese are laughing at me at the 60 yard mark.

[buckhunter]

The steel pellets leave the wad prior to exiting the barrel while the full choke compresses the shot at the end of the barrel.

Steel choke tubes are also made of a more durable metal to resist damage by the harder steel.