Are there any technical limitations about this concept (comparing to the conventional design)?
Yes. Despite what you say, you have made the AR-15 more complicated. You have added at least two springs, another buffer, some pistons, some device for pushing on the bolt carrier, and a housing to put all this stuff in.
At the same time you have created the following problems: 1.) you've put a spring in a place where it would be exposed to high pressure burning propellent, 2.) you have greatly increased the likelihood of carrier tilt (the Stoner design uses gas to push along the
centerline of the bolt carrier,
not the top) and 3.) the added complexity will probably require significant dimensional changes to the handguard and upper receiver, negating compatibility with standard AR parts.
All this to address a supposed problem (lack of a folding stock) that hasn't prevented the AR-15 from becoming one of the most popular rifles on the market. Not only that, but the real or perceived drawbacks of the Stoner design have been amply examined in dozens of more elegant designs over the past few decades (in particular, take a look at the AR-180 and its many, many progeny as well as the Daewoo K1 and K2/DR-200).
I appreciate your interest in firearms design and your attempts to be original. But, take the following from someone who spent a few years doing mechanical design and engineering professionally:
1.) Originality
for its own sake is fun for the designer, but that's about it.
2.) A successful design is the result of answering a meaningful question or addressing a significant unmet need. It
starts with a clear, realistic set of requirements, not vice versa. You need to be much more honest with yourself as to whether the seeming problems you're trying to solve can be done so without introducing many more drawbacks.
3.) I know this is the age of instant gratification, but good design takes a while. Blasting every brainstorm you have across the internet does two things: first, you open yourself up to much more criticism than necessary and second, you negate the patentability of your designs by exposing them to the public before they are protected.
If I were you, I would spend more time learning about the current firearms state of the art. Get your hands on all the guns you can. Shoot them. Tear them apart. Get every firearms book you can and read it cover to cover. Finally, spend a lot more time on the internet asking questions rather than trying to post answers.
