Wow that's neat. Bullet diameter appears smaller than .17 but my eyes may deceive me. Looks like some sort of super short magnum. Waiting for someone that knows more than me...
I don't know about the Walker but .14 is right on. You're good.
I can tell you what I do know. My dad acquired it in the late 60's. He ran into the guy who claimed to have developed it and talked him into selling him one. (He had a number of them.) When asked how it worked out the guy said it didn't. He claimed the bullet pretty much disintegrated not long after it left the muzzle. The parent case by the way is a .218 Bee.