No, it's actually kind of backwards from what you suggest, but you are right that it has to do with fame or popularity of something.
Specifically, the phrase is a reference to trends. When something is "trending down" or "losing popularity," it is said to be "on its way out." If it is a product, maybe it is still available in stores, but it isn't the most popular or talked about item and is losing momentum against some new trend.
The reference is to the "break-in" process. The word process is left out.
A mechanical system, at times, needs a break-in process because the mechanical properties smoothen themselves into place. A typical example is shoes. Shoes need to be broken-in so that they conform to wearer's feet. Another example is new car engines. Cars should not be driven above a particular speed until their engines are broken in. A third example would be the brakes in a car. With those both "broken-in" and "bed-in" are used.
For the gun break-in process, the reference is in particular to the barrel break-in process, although it also applies to the rest of the gun assembly. The gun break-in is also referred to as "seasoning your gun" or "seasoning your barrel". The process is arduous, requiring the user to fire anywhere from 100 - 500 shots from the gun and cleaning the barrel intermittently, anywhere from every 20 to every 5 rounds fired. Also, the process, if performed incorrectly, can damage the gun.
The gun manufacturers basically do this process on new guns beforehand, so that the gun is ready for normal use.
It is both a time- and cost-saving selling point, thus the advertisement.
Best Answer
This seems more like a programming/computer related question to me, due to the feel of the website you got the quote from.
However, it seems that the question is mostly answered by another quote from the same site:
This means that it retires those buffers from use; though, since I'm not a programmer, I don't know what happens to them after that.