You need turrets or some type of BDC scope whether it be mildots or circles or hash marks, and you'll have to know how to use them and match them up.
I personally dont care for BDC scopes. They are busy and I dont like that junk in my scope. I like a fine duplex reticle to where I can see everything. Also BDCs have there limits, you gotta use xxx bullet at xxxx velocity at xxxx altitude, at xxxx temperature and the further out you get, the more that stuff really matters and thats why BDC suck...They are limited to about 600 yards IMO with all things considering at LR... With turrets you can use any load you want, your not stuck with 1 load. Course you gotta cronograph and make up a new drop chart but who cares, way more versatile. You are being as precise as you can with turrents at LR because you can simply dial the required MOA for the type of shot depending on range and conditions, after you input all your data like, bullet weight, fps, zero range, sight height, temp, altitude, pressure, angle, you get the idea right. BDCs just dont win out at true LR shooting for being precise, you'll either be high or low...
You wanna consistently kill or hit stuff at LR you need a rangefinder, cronograph, scope with repeatable turrets, and a good consistent load with a high BC bullet that will open up, and that shoots well under MOA, and you need to have a range to practice out to at least the distance you plan on hunting or shooting at live animals, and shoot often. You need to run the ballistics for the come ups in MOA and then go out and verify. Just becasue JBM says go up 20 MOA at 1K dont mean squat... I tend to practice at 1000-1200 yards that way when somethin pokes up at 500-600, its like a chip shot in otherwords.
It is not cheap to shoot LR. You need a few pieces of equipment and know how to use it, on top of having the time and place to practice A LOT and become good at it.
400 yds really isn't that far though. I would send your scope into leupold and get a mildot. Zero it at 200 or 250 yards, and your first dot would probly be real close to being dead on at 400. I'm not real good with mildots cause I dont use them or like them, but If I had to make use of a Mildot, I would zero at 200 or 250 yards, then I'd calculate, shoot, and verify where each mil down hit dead on at. Thats what I'd do. Reticle change is like $150 or so, and I'd recomend a mildot master or somethign similar to help you estimate range if you dont ahve a rangefinder already. If you already have a rangefinder, hel with the mildot, get turrets installed and start dialing. You dont know what your missing when you hear the sound of steel ringing at LR...