Welcome to BGH String Cutter.

I am not familiar with the Cabelas Hawkins but I assume that sighting issues would be the same no matter the manufacturer.
Sounds like you have a alignment geometry problem if you are shooting consistent groups but low and left.
Sight in has 3 parts, eye, rear sight and front bead. The geometry of these points will determine the sight in point and the level of adjustment available. As you have stated that you have moved the rear sight as far as it will go tells me that moving your eye point would seem to be an option but first try the checks listed below.
Few thing first, Are you left handed? if so is firearm left or right handed?
Check the center line alignment of both the front bead and the center of the rear ramp sight.
Check the center alignment from the center of barrel at the bore back to the end of the stock at the butt-plate. Some slight canter either left or right is normal if the firearm has a right or left hand model, otherwise should be straight or slightly canter to the left.
You might try adding a cheek piece made out of cloth or something and test a few rounds and see if that helps. You can then adjust the cheek piece accordingly.
Thats a starting point. Let us know what the results are and we'll go from there.

For windage with any rifle with open sights I drift the front sight the oposite direction you want the shot to go. I us the rear if ajustable for elevation.

I assume you're familiar with sighting in using open sights, besides JTapia has already explained it, so...

I've had a couple of Hawkins, neither was the Cabelas model, though. Both of them I had to tap the front sight over to correct the group. It wasn't a big deal in the end. I don't know what to tell you about your being 6" low. I somehow doubt that a higher powder load would correct that, but it might help. Could be a factory defect (?) that sounds pretty low at 25 yards if you've maxed out the ramp on your rear sight.

As far as maximum loads, I've never gone above 110 grains. My rifle got a sorta inconsistent at that point, recoil was a little uncomfortable too. I currently use 70 grains of Pyrodex and 275 grain T/C conicals (which I can't find anymore, have to switch to something else when I've used up my current supply). Shoots pretty acurately out to 80 yards. If I plan on shooting farther than that, I just take my .300.

About sights, I just use my factory sights, but I painted the bead on the front sight white. It is much easier to see that way.

I think I got it well enough to hunt with for this season if I keep the shots within 50 yrds or so. Any one know where I can buy better quil. sights for this thing????

my fathers cabelas sporterized hawken shoots everything from the simple .490 round ball with .015 patch and 90gr Pyrodex RS, all the way up to the 295++++++405gr Powerbelt with 80gr Pyrodex RS.

Recently just picked up one in .45 for my nephew to use as his first muzzle loader.

There are special fieber sights (front and rear sight kit) available at Cabela or DGW.

Regards

Kirrmeister