The most interesting item here is 3.5/10mm FSDS round in a rimless case, designed in around 1974 for an experimental MG. Unlike the 4.5/10x54R round shown next to it, which is known among collectors for quite some time, the rimless one is an enigma.
And no, unfortunately this image is not from my collection :(
I have one 4.5/10x54R, but learned about 3.5/10mm only last week, and wish me a good luck ever actually finding one…
BTW, for those interesting in Soviet ammo and able to read Russian, i highly recommend this book, especially 3rd and 4th volumes. It is UNIQUE to say the least, and tells many previously untold stories about development of mass-produced and experimental Soviet small arms ammo:
It’s not cheap (about $50-60 per volume before S&H) but well worth it.