I recently added a version of my Newtonian Dart demo to the upcoming Conceptual Physical Science Explorations 2e Lab Manual.
The trouble is getting good dart guns for this demo. When those of us "of a certain age" were young, these toys were easy to find in drug stores, grocery stores, and--dare I say--the five and dime! You need the classic, hard-stick and suction cup, spring-loaded dart guns.
But somewhere, this type of dart gun was used in a manner inconsistent with its intent. So it was pulled and replaced with safer versions. Bendy, flexi-rubber darts or foam darts were flung by a mechanism that didn't allow for downward firing. And so they were useless for a great demo for showing Newton's second law.
Arbor Scientific has risen to the challenge and found a batch of these classics. I hope they can find a supply steady enough to keep me stocked when mine expire.