False equivalency? Not many people build little ships in bottles, but does that mean they should be persecuted for doing so? Of course not! How popular an activity is shouldn't have any impact on equivalency.
But it does, inside the context of a trial. Nobody's on trial for boats in bottles. People are on trial for shooting fools.
Remember, for a moment, that the key words in self defense are "reasonable and prudent". What constitutes reasonableness? This is actually a question on my county CCW exam, and I can tell you, it's
by far the most popular one to get wrong. Reasonableness is what a hypothetical "average person" would deem reasonable--what they would do. In practical terms, it's what the jury would have done in your shoes.
When you go to trial, you're trying to convince a group of people that your actions were reasonable. How popular those actions are is directly related to how easy it is to convince them. They have to decide that, in your position, knowing what you knew at the time, they would have done the same thing.
Reasonableness is also a "total package" affair. The jury is trying to decide if each individual decision was reasonable, but subconsciously, they're trying to decide if
you are reasonable. For instance, in the Larry Hickey case (IIRC), the police lost Mr Hickey's holster in evidence. With no holster in evidence, the prosecution tried to claim that Hickey was carrying his pistol tucked in his waistband, which most would judge to not be reasonable or prudent. That assertion tainted Hickey with the air of "unreasonable". They implied that if Hickey was unreasonable in his chosen method of carry, then perhaps he was unreasonable about more pertinent aspects of his testimony.
Hence--don't do weird stuff. Don't be an outlier. Do things that are easy and simple to explain. In this instance, what's easier to explain (another subtle point I was making)--
"I carried X ammunition because it has a long track record of use in law enforcement."
or
"I made my own ammo because (see previous walls of text)..."
Now then.....could there be any possible downside to carrying a boutique brand like Buffalo Bore?
Depends on the manufacturer.
I don't know the specifics of GSR testing and how BB's practices might relate to that. I
do have a problem with how they brand some of their selections--their .44 Mag/.44 Spl "Anti-Personnel" wadcutter loads, for instance. But mostly it's a sort of "meh". Not as easy to explain as Speer or Hornady, but understandable.
Other boutiques, like the aforementioned G2 "RIP", or Lehigh Defense, I think you'd have a tougher time.