Hi, hknut,
It depends on what you mean by "prototype to prodcution." It also depends on what you mean by "prototype."
If the prototype is merely a slight change to an existing mode, it could take a few months. If it is an entirely new gun, then a prototype could be just a handmade "proof of concept" that might take years to develop into a working firearm.
A lot depends on financial backing and resources. If the developer is a big company (say S&W), and puts together an experienced design team, working with a top notch model shop, work can be done in weeks that would take a home shop workman years.
Even if a POC can be developed in a short time, and working models made, time will be eaten up in testing and debugging. In the case of the Steyr GB, it looks like Rogak (inadvertently or not) did a lot of their debugging for them, proving at least what would NOT work.
Praise from gunwriters is probably the easiest part. Most of those guys will say wonderful things about any POS they get to try for free, and many praised the Rogak as a miracle weapon. (Mine won't even fire - the mainspring is too weak.)
Why did the Steyr GB fail? Partly because of the Rogak fiasco. But mainly, IMHO, because it is simply one BIIIIGGG pistol for a medium cartridge. Not powerful enough for hunting, too heavy for belt carry in any normal situation, too big for concealed carry, not accurate enough or with the proper sights for target work, it simply had no place in the scheme of things. It seems to have been made just to prove that the system would work, and to build egos, without any real reference to an intended use or a real market.
Jim
