Casting Rangefinder Stalk

So I've been doing quite a bit of casting recently but I've been having issues getting a good rigid cast of my rangefinder stalks. Eventually I've been embedding a piece of aluminum in the resin as I'm casting but I was wondering if anyone else has a different method for making the stalks so they come out rigid instead of having a pliable consistency. I've been casting them in Smooth-On 320 and I've even tried 65 D but nothing seems to work as well as I'd like.

It's really just the nature of the urethane resin. A lot of them will have a slight give, especially at the thickness of the stalk. You may want to try and find a more rigid resin. Alumilite resin is a little more rigid. Or maybe try a polyester resin. But the aluminum embedded idea is used by many to keep the stalk rigid.