Setup: Crossland CC1, Breville Smart Grinder (newer model that does not need shim upgrade)

Bought some dark roast espresso beans from the local roaster; fresh roasted 4 days ago and very oily. Went to dial in the grind on the Breville and had nothing but problems! Grinder down to its finest setting and dosing anywhere from 18 - 20 grams (CC1 does not like overdosing) and getting 15 second extractions every time. Even tried up-dosing until I could barely lock in the portafilter and the extraction time did not change.

Went back to roaster and picked up a medium-dark roused (just short of 2nd crack) roasted on the same day as the previous beans, little to no oil on these guys. Put some in the grinder and immediately choked the machine. Had to dial it back 4 notches and resumed my usual 18g dose for a 27 second extraction.

Just wondering, has anyone had this major of a difference between roasts? Could it also be the oily beans messing with the extraction? Had something similar to this happen in the past but figured it was a fluke, but it happening again made me reconsider. Any tips?

Oily beans can cause problems in grind consistency. My take is that the beans stick to each other slowing the feeding into the throat of the grinder and removing the weight from the bean column that the grinder sees. This would cause the grinds to be inconsistent and coarser. Moving to less oily beans now the grinder is properly weighted by the bean column and is grinding more consistently. Also, if the grinder is new, there will be variations until the burrs are seasoned.

changing different grind settings is completely normal when changing beans.

Factors that affect this that I can think of right now:
size of bean
when it was roasted
oily or not

example: when im dining peaples dailt its 9.4 on my super jolly and when I drink peoples liberation i have to set it to 9.25 to get the same yeild of apporximately 27grams.

IMO don't buy dark roasts. There are a lot of good coffees that are medium roasts.

A dark roast will often take a finer grind. It simply needs a finer grind than your grinder can produce.