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something wrong with your safety?
I took a milspec tube to a table grinder and it worked fine. Forget that paying more for a pistol tube when you have spare extension tubes laying around.
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It does look odd in that pic doesn't it? I checked it just now, it seems the Blackhawk selector detent recesses have a good amount of clearance, but it doesn't appear to impair function or safety.
And I agree on your second point, though I would have gotten an RRA pistol tube for $30 if anyone had them in stock. In any case, the Sb15 appears to be designed to snug up against the end plate judging from the way the mold "locks" into the oval-shaped recess of the end plate. An RRA pistol tube (or standard-length buffer tube) enables this.
The gap just looks sloppy to me, and though the LOP is wicked short, it's actually not unnatural to shoulder as long as you're squared up to the target, much like any pistol ar with the same length buffer tube I surmise.