Look at the rear portion of an AR 15 bcg and compare that to an m16 bcg ( semi auto vs full auto). The semi auto has a little portion cut away so it will not trigger the auto sear in a full auto trigger group. Where as a full auto bcg is fully rounded all the way around behind the space where the hammer swings up and hits the firing pin.
Google full auto vs semi auto bolt carrier, and click images. Just in case my link below doesn't work.
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Whether you'd be able to tell the difference, or I could tell the difference, likely not, maybe, I dunno. Either way, if your rifle is strictly semi auto, a full auto bcg is not required, and shaving off a few ounces of metal doesn't matter to you, then I'd suggest making your decision based on the reputation of the bcg you have in mind, not whether it's semi or full auto. If you require full auto, then get a full auto bcg.
I use a full auto bcg, but have only semi auto AR's. Full auto shoots dollar signs and isn't nearly as accurate. I've fired full auto plenty of times, I'm over it.