I usually sample larger sample than what I want. Say 5 bar (or 4 bar and a little more)
Then I put a trig on the first step with infinite trig len and start the sequencer.
Adjust the tempo and the tuning until you get a smooth loop.
Go to pattern 2 and put a kick or a snappy sound on the first step.
Go back to pattern 1 (where you adjusted your loop)
Go to sampling page and sample to MAIN L+R. Put a threshold high enough to not run the recorder when you press yes.
Press yes to arm the recorder.
Press Play, and change to pattern 2.
The loop will run then BANG! and silence.
In the audio editor, cut the bang sound and you have your perfect loop.
You can use my trick to quickly chop your sample then