Anyone remember the Monolith P-12?
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Evidently it didn't work/was vaporware, but the concept would be tits as an autoloader if it functioned.
The Rumor is that Magpul bought the design and did what Magpul does when it come up with a cool design (PDR/FMG9), that is stick it in a filing cabinet and forget about it. Then again they finally put the plan into motion to make the FMG9 a decade and change after its reveal but that has been a multi year saga and they're still not shipping preorders.
I was made aware of an interesting Ukrainian straight pull(as there is no gas system, the charging handle is used to cycle the action) integrally suppressed rifle The Hopak/Gopak-61 (I have seen it spelled both ways)
It is a Mutilated AKM with a PKM buttstock for some reason.

ARES Article about the gun
The only footage of it I can find actually being fired occurs from 3:55 to 3:58 in the linked below video
In a similar vein here are some videos about guns that are not too dissimilar to the above rifle but American made. The third video actually goes a little into actually making one.
A new photo of Developer Instructive Content's 2nd generation 5.45 Helical AK mag
An update to the Shotstop Armor controversy

Warrior Poet Society/John Lovell, who is mentioned in the above posts responded saying that they have stopped all sales and promotion of "these" plates. (unclear if they mean Shotstop Level IV's or all Shotstop plates)
Lastly we have some wildcatter/Reloader ASMR
A video detailing the process of creating .357/45 GWM( A .45 Winchester Magnum case necked down to .357) Brass from .30-06 and family (.308, .243) cases
A three part series on making .45 ACP shotshells
A similar video but for .38 Special
Lastly we have a great but sadly inactive channel, The Ammo Channel and it's archive. Several videos not available on youtube are preserved in the archive.
This guy did great stuff, lots of neat tests of various projectiles, DIY reloading stuff, gun builds and lead smelting/casting.
Wayback archive of screenshots from his now defunct website.
@Seafarer
The creator of that gun is this guy
He has several other videos.