To me, the only major and glaring design issue behind the AR-15 and similar two-receiver designs is the interface between the two receivers. By using only two pins and having variable tolerance between them for mass-manufacturing inevitably leads to excessive slop. This is compounded by the choices in materials as steel rubs on aluminum receivers (but that is another issue entirely).
Various “solutions” to the issues have cropped up over the years to various degrees of success. The most prominent of them are the “wedge” and “screw” style tightening systems which put upward pressure on the rear lug. This works, but it does have its own set of issues and in extreme cases after wear, the weapon malfunctions as the alignment of the carrier to buffer is off.
In to provide a more neutral positioning solution is JP Enterprises. Rather than relying on various tensioning methods, JP has opted for a precision method with their new MicroFit pins. Basically, they are standard pins controlled to a tightly ground OD offered in various sizes to allow one to fit the pin to their gun. JP currently offers three sizes. Standard, under, and over, which are .001″ smaller and larger, respectively.
Knowing the fitment will be tighter, a recess is added to make it easy to get the pin out with a punch or bullet tip. All are polished and QPQ Nitride finished.
Pin sets are available for $28 or individual pins at $15, each. They can be purchased directly through JP Enterprises of JP’s dealer network. MicroFit pins are available for both the AR-15 and LR-308 platforms.