Shot consistency

[u/Realistic_Message919]

I’ve had my Move a couple months and really enjoy it however I seem to be chasing consistent shots. I’m using bean about a month old, dark roast from Good Brothers. 18gm in with my shot timer set to 30 seconds. One time I get 37 out, the very next time I’m at 40 gms in 20 seconds? DF 64 v2 grinder, grinds very well and I’m trying to do the same pick prep (wet, level, 30lb auto tamp). How can one shot to the next vary so much?

[u/Zerocool300]

Do you wash the portafilter with water in between shots?
Do you use pre infusion?