I'm having some issues with sampling and looping.

If I sample an old rock / RnB song for example, by the time I loop the 4 bars the dymanic changes and you can hear the loop.

Are most people re-recording their samples? I feel like it's the only way to get the samples I want.

Another thing, is it's hard to get the sample I'm looking for without vocals.

This may seem like a lame question.

It just seems easier for me to write all my instruments or re-record a sample I have.

Or maybe the art to sampling is finding the beat that sounds the same when looped and finding audio with no vocals etc.