The main selling point on a Shrike is that it's a belt fed weapon. The picture of the Shrike you posted is about as close to an actual Shrike as a Nerf rocket launcher is to an RPG-7.
So if you're not going for an actual Shrike, what you're left with is an M4 with a drum mag: just get a C-Mag or something, get an SPR flash hider an a slightly longer inner barrel.
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