I bought A LOT of this back in the day.  I have an ammo can with a few hundred rounds in it, still sealed in those cell packs it came in.  Is it collectible and sought after at all?

Not really collectable. About a gazillion rounds were imported, so they are very common. The corrosive primers scare some people away, as does the price. Back when cases of it were available, it was dirt cheap. Now you see smaller quantities priced like regular ammunition or higher.

I let me kids go crazy with it in the RPD.  Should it get away from them I'm not worried about where they go since there is nothing for 300 yards past my berm.

They are also fun to mag dump on New Years Eve.

Down to about a single fat 50 of them left now.

They will go much farther than 300 yards.

The East Germans trained with them out to 800 meters. These are often mistaken as "short range" cartridges. While they do have reduced downrange danger-space on purpose, the EGs called them "Ubung" or "Practice" ammunition.

IIRC, each crate came with a sheet of paper showing what rear sight elevation adjustments needed to be made to accommodate for the bullet drop. The adjustment for the RPK (for example) was setting the sight at the "10" to hit at 800 meters, and so-on down the ladder as range decreased.

Honestly I’ve used them a lot, they will splatter pumpkins etc, go through thicker plywood like nothing, it’s my opinion they would be terribly effective on soft skinned unarmored targets, varmints etc.

Thanks dudes.  I bought them for $49/1K from Centerfire Systems.  Crazy in retrospect.

I use this ammo in my 107cr SBR with a Dead Air Wolverine.  It cycles in a 12.5" (with the help on the Silencer) and is extremely quiet and soft shooting (KNS adjustable piston).  I do however  get a couple bad primers during matches (2-4 per 120rnds).  Corrosive as previously stated but didn't see any rust issues in the Wolverine besides on the removable end cap.