Slide Fire Solutions has developed a stock for the AR-15 that facilitates bumpfire shooting. It is reminicint of the ill fated Akins Accelerator that was initially approved by the BATFE but later deemed a full-auto device and banned.
I am not sure quite how this works, but the BATFE approval letter and the Slide Fire website indicate that there are no mechanical parts.
It seems to be using the buffer spring to provide the forward “bumping” force UPDATE: It requires the operator to provide muscular forward force . This is unlike the Akins Accelerator which had its own spring system. The lack of any mechanical parts may be why the BATFE approved it.
Side Fire have it listed for sale at $319 on their website.
[ Many thanks to jdun1911 for emailing me the link. ]