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The coffee is around 13 days after roasting, so not super-fresh but not too old either. The grinder is second hand so maybe it's the burrs, but not so long ago it was grinding OK until I decided to try and fine tune everything and therefore fucked it up.
It's a timer grinder, so dispenses as much as it does within a certain timeframe. And that isn't consistent, if I'm honest. But I grind into a dose cup and weigh it anyway, so the dose going into the portafilter is always the same.
The machine is pretty new (three months), so I'm assuming nothing's gone wrong with it yet. No pressure gauge, but it should all be working as the manufacturer intended. I clear the screen after every shot to make sure there are no grounds sticking to it, so that shouldn't be an issue either.
The basket is stock and probably shite, but I have an IMS Precision arriving tomorrow, which should sort that out. Also have one of those WDTs being delivered, so I can faff a bit more with the puck preparation. Hoping this will at least help stop the channelling so I can then move onto ruling out other stuff that's fouling my shots.
ketsbaia-
Coffee freshness is pretty much ideal then.
You’ve got all your variables under control, just pump pressure is unknown so I’d look at that. Some machines ship with the pump at max pressure. Check to see whether you have an adjustable OPV on your machine, then see if you can borrow a portafilter pressure gauge to see what you’re getting
Stevethecoffee
How fresh is your coffee?
Did you buy the grinder new? - could the burrs be dull?
Are you getting a consistent dose of ground coffee?
That’s the dry side of things, then check the machine is in good order - correct pump pressure, dispersion block and screen not obstructed by scale or dirt. Maybe get a new basket in case the holes have gone wrong.
Tamping just takes diligence but you can get all that fiddly kit that takes the guesswork out of basket prep.