I've attended a lot of Front Sight courses. You'll be just fine with your G19. My first course with them was using a SIG 228 with cheap Chinese ball ammo. No probs whatsoever. Naish Piazza, the director used to carry a G22, not sure what he's running these days.
Despite the above advice, Winchester White Box is very common out there and will run in your 19 just fine. No experience with BTF so I can't speak on that. Most importantly, bring drinks, sunscreen and snacks. I'd bring a band aid or two for your magazine reloading thumb too. It'll get a workout by the end of 4 days.
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