RBF (Reinforced Buffer Retainer) is a drop in replacement for TDP spec AR15/M16 buffer retainer with 10% larger diameter tip. RBF is machined on Swiss machines with tight tolerances in 17-4 stainless steel, and heat treated to H900.
10% increase (0.102 vs TDP spec 0.093) in its tip is all that's possible without creating timing issues with REs and lowers. Every lower receiver and RE can have different timing values. RBF is compatible with TDP spec rifle and carbine receiver extensions, as well as our favorite, the Vltor A5 system's RE-A5 and RE10/A5SR receiver extensions.
We eschewed a rectangular tip design found on the HK416, as we believe it will cause more problems than it solves. On the HK416, its buffer retainer is pinned in place. On TDP spec AR15/M16 lowers, such a buffer retainer will not be pinned and prevented from rotating, and we're not confident lowers/RE timing is sufficient in all cases to ensure the retainer doesn't rotate sideways and block the carrier from traveling rearward into the RE.
RBF doesn't require timing as its tip is round like the TDP spec buffer retainer it's based on. We chose 17-4 stainless steel because of its durability, and heat treat it to TDP spec hardness. RBF isn't meant to be a fix for out of spec lowers, it is designed to have better endurance than factory buffer retainers.
Whereas a factory buffer retainer would have failed, RBF with its better material and strength provide better fault tolerance. RBF can't fix tolerance stacking, it does provide the user more time in which to replace/address these issues.
In the picture below, tolerance stacking issues created a gap between the rear of the carrier and the buffer, when the AR cycles, the buffer hammers the buffer retainer when the retainer should be free of any load, let alone being impacted from the buffer repeatedly. Significant wear can be seen after 800rds on the RBF, but RBF has continued to function where a factory 8620 steel TDP spec buffer retainer would have failed.
It is also evident the RBF has rotated, the impact has worn its tip all around. This is the reason we believe a rectangular tip without the buffer retainer pinned in place as the HK416 has done is flawed. TDP spec and RBF can rotate without ill effects. If a buffer retainer with a rectangular tip rotates with its broad side being angled or worse, perpendicular to the bore, it will block the carrier from traveling rearward. Adding another source for potential cycling problems in the name of strengthening the buffer retainer isn't our idea of problem solving.