IMO the light is to far away from the tops.
If it was mine i would bend the top cola over on the biggest plant and try to get the lamp 8" away from the tops.
All though your plants are looking fairly healthy they are stretched and the buds are small.
The leaf curling that you see is also probably to do with keeping your soil to wet.
Roots/plants need oxygen.
Please don't take this the wrong way i am trying to give you the best advice i can
All very good advice & accurate too,i would like to add a few things to natmoons list.
Right now i see light being the biggest issue,you should get that light no further than 12 inches from the canopy,no matter what you need to do in order to accomplish lowering the light without frying the plants you need to make it happen,big bud can produce some massive dense buds but without intense light they will be nothing special.
You did not mention nute's,what nute's are you using & have you thought of feeding them molasses,i used black strap molasses on my big bud's last grow & was pleased with the results,it added a small sweetness to the taste & added a bit of weight too.
Your choice of pot size has me wondering also,when natmoon says roots need oxygen he is correct,large pots with large amounts of soil that remains wet for days are not in your best interest,i watched a few things that FDD has done with smaller pots & have mimicked them on this grow,what ive found is that large pots only offer room for roots to grow but they have a serious drawback & that is oxygen delievery to the roots.
Think about this for a second because it goes against the grain of growing in soil,when doing a hydro grow the main benifit is increased growth rate & yeilds,both these benifits are directly related to oxygen delievery & nutrient uptake to the roots,hydro systems are watered at minimum once a day bringing fresh oxygen to the roots at an increased rate over standard soil watering pratices.Smaller pots dry out faster allowing you to water more often,with watering comes oxygen which is more important that any flowering nute's could ever be.
Ive switched over to 1 gallon pots & have noticed increased growth rate in veg,ive not made it to bud with this grow yet but from what i see so far the smaller pots are bringing the speed of the grow more inline with the speed of a hydro grow & totally eleminated the possibility of slowed growth due to over watering or water build up at the bottom of the soil.
I have 4 Big Bud outside and they are growing well. Keeps us posted.
