... thanks to Harvey's research at UCLA, there's a better picture about what happened [re the phaser rifle]...
The Phaser rifle was built at no cost by the Reuben Klamer Toy Development Center in Beverly Hills. Klamer is famous for having reinvented "Checkered Game of Life" as the "Game of Life". He is also credited with inventing about 200 other toys.
I have informed Reuben Klamer of Toy Development Center, Inc. that he is to proceed with development and fabrication of one (and if possible two) STAR TREK Phaser rifle for use in episode #2. His firm will plan and execute it at no charge to us in return for certain rights in the product as discussed between you and him at this week’s meeting in my office. This particular arrangement applies to this Phaser rifle only.
July 2, 1965 memo to Ed Perlstein from Roddenberry
So, it was Klamer's group that built the rifle. Note Roddenberry says "plan and execute", which implies they designed it.
...in any such arrangement would be in how much your craftsmen and shops can help the STAR TREK production unit in creation of items we may need, and even more specifically in design and fabrication of items which our writers have built into their scripts.
March 16, 1966 memo to Reuben Klamer from Roddenberry
So, once the series was a "go", Roddenberry was discussing with Klamer the possibility of having them make props, seemingly in a deal that would have been similar to what eventually happened with AMT.
I am sure Robert J. has told you this, but I am very much in favor of blowing the Klamer deal. In fact, let me be more definite about it -- I feel if we have this much trouble at this point, it would be most unwise to continue since they seem exactly the kind of people who will hang us up a few days before shooting and we would be in great trouble. We are proceeding with Matt Jefferies and a model maker based on a design which I gave Matt yesterday, a design which very much sets our thematic needs and still has considerable toy implication.
April 22, 1966 memo to Ed Perlstein from Roddenberry
A month later, Roddenberry's had it with Klamer and is deciding to pull the plug. There's no indication that Klamer delivered any unusable prototypes, just that they are having difficulties.
Finally...
...As of this moment the entire matter is dead. If Klamer wants to work with us on any particular item he will first have to submit it to us and then after deliberation, we will determine whether or not we will proceed with him. Please rest assured that Klamer is not involved in the phaser rifle, phaser pistol, transicator or any other item.
April 22, 1966 memo to Ed Perlstein from Roddenberry