With the cartridge chosen, it is time to finally set up design requirements for a weapon.
Harel Cseh wants a light practical rifle that will be available as soon as possible. Magazines don't particularly matter to him, and he's admitted that they're honestly extra weight. Single shot is good enough given how long it would actually take to reacquire a target after firing anyway (although Cseh grudgingly admits a tripod or sled mount from a Holborn or any of the heavy MGs would cut that down drastically.) Maybe it could have a little cartridge caddy if there was time and money for it. As for a machine gun, some Holborn derivative will probably be good enough, but something lighter might have some use elsewhere.
Sandor Ivalko wants the lightest practical machine gun for AA work and fitting onto existing armored cars, and while not as aggressively austere as Cseh, is skeptical that a magazine system is really worth it. That said, Ivalko is willing to add more weight to control recoil better and speed target acquisition times. Maybe even something with a flash/recoil suppressor on it to help with gas mitigation and prevent the rifle from being easily spotted.
Josip Kaldhoff wants a heavy machine gun capable of sustained fire, that can be maybe converted to a lighter aircooled version for the infantry and lighter armored cars. A single shot rifle is fairly useless in his book, so at a minimum he wants a semi-automatic action with a ten round magazine, that can fit on existing MG mounts. Flash suppression is obviously a requirement for night fighting, and would help the crews stay concealed, since surprise is a necessity.
Parsival Smyd doesn't have a dog in the machine gun-rifle fight, but thinks the need for recoil management is a bit overstated, since even the lightest rifles are going to be 40kg and fired from a bipod or a heavier fixed mount. And well, a machine gun for this is probably going to be fifty kg and fired from a fixed mount or a multi-ton vehicle, so that's even less of a problem.
Herceg Kaila is thinking more about practical applications at the moment, but he is pretty serious about a light rifle, using some heavy springs to manage recoil, and add a bit more weight to the gun so it stays emplaced better. That said, outside of a "light" 14.5mm machine gun like a Frankengatsch for existing vehicles, Kaila is pretty insistent that the way forward for 860 and beyond is going to be a dual role AA/AT machine gun, and a watercooled one at that. A rifle would be a really good stopgap for now, and there's plenty of people around who could cook up one that could be produced with a month or so (after all, the sleds and test barrels were designed and built in a weekend.) A flash suppressor for something like 14.5 would take a lot longer though.
SR Tidur thinks Herceg Kaila is being really optimistic about timescales, but does think that a practical and effective rifle could easily be produced by the end of the year (in four months or so.) That said, a Machine gun would take a year at least, since they're far more complicated. Tidur also thinks that while a rifle might not be effective alone, a section of them focused on one armored car will play the numbers well enough, so cost and ease of production should be the priority. As such all unnecessary luxuries should be dispensed with.
With opinions in hand, you can begin to sculpt requirements for both categories should you choose to have them. This will be Vote By Plan, with Rifle and MG blocks, so make your own votes.