I just noticed that some of the Engel’s Collectibles lots are now live on the website. Looks like some nice items!
Headstamp is WCC 85 on my specimen. That puts it in the era of the adoption of the M858/M860 Blue Plastic practice rounds. I don’t know for sure if this was their attempt at getting the contract or some other effort. Besides the grey projectile (I’ve only seen on this board), there were Black, White and Blue plastic flat tip (WCC 86) examples. There is also (maybe an unrelated project) of a Blue plastic round nose (WCC 86) example. All were on brass cases, rather than the BF blue plastic cases.
50m2hb, the date could make sense then.
Are any images available of those you have mentioned?