The presence of slack between upper and lower receivers of AR-15 pattern rifles is sometimes considered a flaw of the design. Some people insist that it does affect the accuracy, others just find it annoying. In order to solve this problem, different manufacturers came up with various solutions. Perhaps the most known are the tensioning pins by JP Enterprises, but there are a couple of other products too (tensioning screws etc.).
A company called F&D Defense has a different approach in eliminating the wobbling of upper and lower receivers. They make a lower receiver which has a special contour (sort of a raised bump) which puts the required amount of tension to any upper receiver mounted on it. This system is called SHUT, which stands for Solid Hinge Upper Tensioning. Watch the video below to have a better idea of how that works:
Although it looks to solve the problem, the obvious drawback is that you have to buy a new lower receiver. In the case of tensioning pins, you just drop them in and you are good to go. Perhaps for a new precision rifle build it would be a good choice to get this receiver, because it seems to be a more solid way of removing the receiver slack problem. The question is … is it a problem at all?
The MSRP of F&D Defense AR-15 receiver with SHUT feature is $119.99.
F&D Defense HQ
Address: 201 W Oak, Seminole, Oklahoma 74868