Which knob on the bushnell banner scope will raise the bullet when it is hitting six inches low?

you might be able to buy a weaver rail adapter that can change your elevation aswell as lift up your scope a bit just to make it a bit easier to see out of. try something like this maybe http://ant-supplies.co.uk/DovetailtoWeaverAdapters.aspx

You need a shim to put under your scope base. Brownell's sale the kits for them.

I'd start by looking at the mounting bases.
First tighten the scope ring screws to 25 inch pounds, then loosen and remove the rings from the base(s) while still attached to the scope.
Back out the base screws one at a time, apply low strength thread locking compound and tighten each to 25 inch pounds.
Remount the rings/scope to the bases tightening till snug but not overly tight and sight-in the rifle.
Hope this helps, Mark the Gunsmith

! click is 1 inch @ 100 yards, provided you have the correct scope for the rifle.
If you are sighting in a .22 LR 40 grain match velocity bullet for 100 yards, the mid range trajectory (50 Yards) is 6" higher. The bullet has a 6" arc half way to your target. If you are sighting in a .270 with 150 grain blunt tail bullets for 250 yards, the mid range trajectory is .4 higher. It only has 4/10" arc half way.
You most match the scope to the gun, and the 1 click= 1 inch rule will apply. Otherwise, it's lock it into a righd mount, fire it and adjust the scope accordingly. If you want to change the range on the scope, it will be guesswork.
I use a Bushnell Banner 3-9X40 with BDC. If you have BDC, make sure you have the correct distance ring in for the caliber.. It will make all the difference in the world.

the top knob should have up or U with an arrow on it showing which direction to turn it

The top turret should be the one you need. You should see an U or D with an arrow pointing in one direction or another. Your scope should move the point of impact 1/4 inch at 100 yards for each click. Moving the adjustment 24 clicks in the down direction should fix you up if you are shooting at 100 yards. The movement will be linear for other distances.

Take it to a well stocked hardware store and see if they have a screw that will work.

It sounds as if your Scope rings are out of alignment or the front ring is lower than the rear ring. You may be able raise the bottom of the front ring by inserting a shim under the front ring base.

This happens will all firearms. what happens when the bullet leaves the bullet is a decieving "rise" of the bullet. The reason for this is the Line of Sight (Scope View), angles down and away from the Line of Departure (Barrel). The bullet actually never rises and is in fact continally falling away from your rifles Line of Departure but because this is higher than the Line of Sight the bullet seems to Rise than fall to the set distance in the scope (i mention set distance and not zero because you can change your Minutes of Angle on your scope to increase and decrease range)

http://www.rifleshootermag.com/shooting_tips/ballistics_0303/

this is a chart that illustrates what i just said.

now that you understand that you should take a good read into Exterior Ballistics. this is the Mathematics of your fireamrs trajectory ( I say your firearms because your bullet's flight depends on the length of the barel which will vary from gun to gun) this science of shooting will teach you how to understand bullet Grain and Volume relations. understanding the Feet per second of your rounds and how the affects you. teach you about shooting in high pressure and low pressure environments and extremly windy environment.

now there is alot of math to all of this and its hard to find it all on the net and if your not that great at math you can do what i do bc im lazy and im not a sniper im just a hobby kinda guy. '

Sierra Infinity V 6 Ballistics Software. I dl'd mine off the net you might have to buy it depending on how resourceful you are. it is well worth the buy. You can punch in the daily variables (Barometric Pressure, Temp, Humidity, and Altitude) (of couse with your bullet as well) and it will give you a "Cheat Sheet" for those conditions stating Windage and Elevation adjustments per decided incriment (50 yrds is standard) then you take that to the range and (bring a laptop if you got it and arent embarrased (som1 might even help you tune in the variables) hope this helps if not ill check back in a bit to see how you did

Try reversing the rings. Move the back one to the front, and the front one to the back. Turn your elevation adjustment, back to -0-, and start again.