Good news: MP-156, Baikal’s first inertia autoloader, is not as bad as my previous post made it sound. IzhMech responded to the customer complaints, and improved their guns significantly. The quality is still a lottery. But, while in the first lots the share of lemons was as high as 50%, today at least 9 out of 10 guns perform well out of the box. Not yet in the Benelli league, admittedly, but that at least makes it worthwhile to say something about MP-156 design.
Most inertia operated shotguns have the inertia module, with the spring that is compressed when the gun recoils, and expands to cycle the bolt, inside the bolt. This is the optimal solution, as it makes the gun more simple, compact and light – and, apparently, more reliable too. With MP-156, however, Baikal took a different route.
If you look at MP-155 and MP-156 parts lying next to each other, you may have a problem telling which is which. Because Baikal placed the inertia module right where the MP-155 has the gas piston! The logic was to simplify the production. With this approach, IzhMech can use not only the same receiver, stock, trigger assembly and barrels, but also the same bolt, and the same action links, to make both the inertia MP-156 and the gas-operated MP-155.
Needless to say, it doesn’t deliver the main advantages of an inertia gun: less weight, fewer parts, and better balance. There’s no free lunch in Newtonian mechanics, and the inertia spring now has to do extra work moving the additional mass of the action link and the inertia module body, with more losses on friction, bending in the action links, and more. The links may drag on other parts of the gun, leading to jams, too.
If I know anything about firearms, this design will never be as light, simple, and reliable as a conventional inertia-operated shotgun, all other things being equal. On the other hand, there are quite a few Russian gunners who are quite satisfied with their MP-156. I don’t think I’ll ever get one (in fact, last year I was offered an MP-156 for free, and declined the offer, as politely as I could). But you’re free to do with your money what you wish.
Photos (c) the Kalashnikov Magazine.