I have a Great Plains 2N-3010 drill and have for 23 years. Use it for wheat, cover crops, and mostly soybeans. Has no-till coulters(fairly new), new openers, new Keetons(removed firmer wheels), 2" smooth gauge wheels, and a two row tine harrow, I always have had trouble with inconsistent depth. I can get half of the beans at the 1" target depth, but there are always a few on top or nearly so, and a few at 2 or sometimes even 3" deep. The ones on top only come if it rains, and the ones at 3" deep only come with a lot of prayer. I can set the coulters shallower but then don't get penetration in hard spots. I don't like 30" beans for several reasons and have done yield checks to show it's not just a preference for me. What can I do to help even the seeding depth on the thing?
Is a 15" planter the only sure way to get good depth control?