Thought I'd post an after action report on installing the OPS-416 system with a Seekins rail using their new 'piston friendly' barrel nut. Project is an SBR (11.5"). The OPS-416 kit was just laying around and 11.5" is the minimum barrel length supported by the system.
The kit comes with a standard operating rod (carbine length) and I have a modified operating rod for larger barrel nuts that I acquired via an arfcom trade.
The new Seekins barrel nut was made 'piston friendly' by adding four relief cuts to the nut.

It's too much relief for the modified operating rod, as the piston can
travel completely free of the piston chamber.
The standard operating rod is required with this nut, but the shank
needed a little extra clearance through the relief cut. Broke out the dreaded Dremel and
removed a few mils of material. Took five minutes and it's dead simple to do. Polished it up so it doesn't look like a hack job and blackened the aluminum with some acid. The only tricky part was timing the nut back on to get the right slot lined up.





Pictures of the rifle will be posted later in the piston photo section.