When I first look at the bullet it reminds me of a Winchester which I may have seen years ago?? Ok as for the Speer Grand Slam, I looked through my books Speer #5 to present #14 and could find nothing nor in my mind that would remind me of a Speer bullet. I pretty sure Speer at one time manufactured a 168 gr match bullet, years back in .30 caliber that had a "rebated boat tail" for some reason they didn't last long in the market place, I'm thinking because rebating show no real advantage in drag reduction comparing to conventional boat tail bullets of similar length.
Now with that said; here's another thought on your bullet. Could it be a custom built bullet? The type made by using a Corbin RBT die swaging system. The more I look about it; the more it's has many of the signs of a custom bullet'.., the kind where you could make a 168gr bullet in 7mm with a rebated boat tail and double cannelure by using; the RBT die and a Corbin's PCM-2 cannelure machine; as well as other cannelure machines which do a fine factory looking cannelure job.
In the rebated BT bullet design it's looks close to the Lapua 185gr D-46 (although .30 cal) however they do looks like, along with some of the older JLK's & NwCP's as I recall.
This is just my best guess… there are many crazy European designs that could be thought of at this point.. but that makes my head hurt.
Good luck.
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