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I’m ticking most of those boxes. Heated portafilter, grinds into metal cup.
I’m really making sure it’s even in the portafilter, and tamped level etc.Will try again this afternoon. But I think finer is the key.
Nef-
Agreed that looks like it needs a finer grind; how much espresso did you get in those 27s? Seemed like a lot. Don't think it'd be the tamping that's the issue. You sometimes can get less channelling if you pre-infuse (I think the Mr Shades PID - which I recall you have? - has that functionality?) because the puck is given some time to expand evenly before being hit with the full 9bars of pressure. I might disagree with @jonny69 and think that WDT is probably the best thing you can do to distribute and break up clumps, and I think the leveller is pretty efficient to use if you've got it (does the same thing as tapping against the palm but faster). Although I never bothered with either myself because the Sette made fluffy grinds and I preferred to live with the occasional spurt out than increase prep time by 30s per coffee/get all the extra tools.
youClown
Sounds like you still need to go finer. I’m tempted to say put the WDT and leveller aside for now and use a conventional tamper until you better understand what’s going on.
Back to basics:
Heat the portafilter: run a bit of water through for 5 seconds or so, so that you’re not pulling your shot through a cold portafilter.
Static reduction: grind the beans dry into a jam jar or metal cup
Clump breakup: gentle shake side to side.
Even dose into the portafilter: wipe the basket dry. Pour the coffee in directly and evenly. Use a dosing ring, but don’t use a teaspoon.
Even the distribution: level it out by knocking the sides of the portafilter with your palm until it’s level.
Tamp: tamp evenly, gently at first, check, then tamp again firmly. If the tamper goes in at an angle it’s probably due to uneven distribution.
Clear the side walls of the basket: quick tap on the sides of the portafilter with the tamper will knock the loose coffee off the sides of the basket. Then just lightly tamp to smooth the top and re-seat the puck of coffee.
Gaggia Classic likes a big dose and to pull a big shot IME. Don’t leave too much (if any) headspace.