We submitted a lower receiver to the RCMP lab that was designed to accept the Ferret 50 cal upper. The upper was extensively re-worked so that it could not be attached in any manner to an AR15 lower. The proprietary lower was designed to be an inch longer than an AR10 lower, had no take down pins, no mag well. The upper was then bolted to lower.
The lab guys used duct tape to attach an AR15 upper to our lower, and managed to get a primer strike discharging a primer. The issue here is that if a live round of 223 had been used the bolt would have become part of anyone who fired it's head as the upper of an AR projected over an inch above where the solid buffer tube of the lower is.
They deemed the Gen lower as restricted. We took .060 off of the top of the hammer and resubmitted. There is no FRT as despite the lower having the serial number etc. it was classified as a trigger group only like the Swiss Arms lowers. Now the real corker here is that this was back in 2008 when the registry was in full force. I brought this detail to the RCMP guys attention and was told that the upper was to be the part that was registered, despite the fact that they are not serialized parts, but the answer to that was "the sticker".
I still have all the E correspondence and letters.
Fact seems to be weirder than fiction.