Unknown Plastic Flare?

Here is plastic cartridge. It appears at some time it was unloaded. It may have been a flare but that’s just a guess.
The headstamp in “PAT. PEND”
Rim Dia. 0.515"
Base Dia 0.456"
Case mouth 0.463"
Case Length 1.569"

Any thoughts?


If rim and base measurements are switched then i would guess a .410 shotgun flare.

Then again in the 1960’s all plastic cases were the fad.

The base should have read 0.456 in. I’ve corrected it in the original post.