That is a huge question. This is for the Mac style family of registered receiver machineguns? Is this unit based on a current design? How available would parts be? What caliber? How available are belts or links?
We at A&S Conversions are still working on the Tenko adapter. Here is a video of my brother shooting his Shrike on an early Tenko 10-16:
https://youtu.be/zU5XkqnewFw
Here is me shooting a similar Tenko 10-16 with a 9mm belt fed upper:
https://youtu.be/k_6PoOZDTzI
The current design has the same function but required modification to locate internal structures to please the ATF. I am heading out to do a final test before submission. If everything goes well I will post a separate update.
Is there a market for a belt Fed? Certainly, but how many units could a creator expect to have to defer their R&D cost? There is also the issue of remaining in business. Once those initial bunch of units are sold, how many units per year could be expected to be sold? Look at the tungsten bolts and Lage rifle caliber uppers. One the initial production is completed how long will it take to build a list of potential buyers to make another run? Could such a limited market produce enough profit to have a manufacturer develop, build, and retain parts availability?
While such a poll is fun to dream about a belt fed upper coming to market, I would imagine such a product would be in the $6,000 to $7,000 price range at a minimum. Could the MCR be adapted to the Lage upper system? I would think so. But I for one would be very weary of the owner of FightLite.
Scott