when the shots hook one way or the other. I've got a well MB10 coming and the last time I had one it hooked and I forgot how I sorted it. Hopefully it won't, but just planning ahead
If it's not the bucking it's the orientation of your scope - the guide is a video whereby you shine a torch down your scope to project the reticule onto a surface then make sure it's properly in line with the barrel. Well it'll be your nub or a damaged/not properly seated/poorly formed bucking so I suppose that's where to go if aligning the scope properly doesn't work.
Look for the TDC mod, details can be found on Airsoft Sniper forum, basically glue a nut to press down directly on to the hop arm. The hop arm due to its configuration can twist slightly applying uneven pressure on the bb giving the normal hop effect with a diagonal axis sending shots sideways consistently. Relatively easy to do if you can hold your nerve as you drill the outer barrel.
I was tempted to just grab an AA chamber, used them in my last few builds. But from what I've been reading a standard hop tuned well will still perform.
I'd still get the AA chamber simply because the seal is so good and it holds the bucking much better. You can still get excellent results with the stock one of course.