Update FWIW: Couple days ago, dremeled the bejesus out of that end cap. No way Jose, just not gonna get there. Ordered the BCM end cap I noted above, and waited for it and an upper to arrive.

Today, both pieces arrived, went together like a charm. There was just enough differences in the end caps to throw off the alignment, although I would have had a hard time believing it if I hadn't seen it myself.

I just wanted something simple and cost effective for my first build. Maybe I'll go back and put a 'spensive rail on it someday but today I'm just happy it went together.

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