7-08 maybe
Not 7-08. Case too big.
7mm suam maybe
Errr Weatherby?
AK-47 cartridge.
Um 7mm BR?
Nope, nope, nope & nope.
See if this helps…
7mm grendel?
Guess again.
Is it 7mm diameter?
284 Winchester?
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Bingo. 284win.
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.45-70 with sabot and monolithic .38 brass bullet.
[trans: I have absolutely no idea and that’s the only straight wall rifle cartridge I know]
Nope, Way off 
24 guage brass case?
Considering who posted it I’ll guess, brass case .410 slug ?
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Nope and nope but you are on the right track.
It’s a 585 CEB bullet in a 12ga super sabot. Got it off the internet…easy.
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