How do you set a bpm and/or beatgrids with acapellas?
Anybody know how to do this? All I can think to do is set an estimate bpm manually and tweak it till the grid falls into place.
Grab a copy of the original tune and get the bpm off that. manually input this bpm into traktor, turn snap off, and lay those grids down 
+1 w/Jester
Still some trial and error involved. Little practise and you’ll be a legend! I use some tripped out movie samples etc but they aint from songs and don’t have a defined tempo so i just set them at 145 and program the loops from there.
If you have access to fl studio , Set up a loop in the bpm range you run in, lets say 128bpm. Import your sample and you can timestretch it to fit using the quick loop as a template.
+2
+3 although this is a major pain to take buy both versions 
take a basic 4-on-the-floor house sample (deck a) and set loop size to 4.
Turn down the hi and mid EQ and set the acapella sample in deck B. Try messing with the 4/4 sample to get the tempo right for the a capella and then set the tempo for the a capella to that tempo.
Use Mixmeister BPM analyzer, is so good that it even gets the tempo of the accapellas right, then you only have to copy the bpm to Traktor.
If you listen to it it’s pretty easy to get the bpm following the beat with a foot on most acapellas.
If you’re able to do that then go the tapping route inside traktor.