Bit high
grouping 4 feet high at 100 yds sounds like a pretty dramatic problem. Are you sure the barrel isn't bent or something? It will also depend on what loads you use, but even with that variable..... If it is really that far off at 100 yds, you might have to make some kind of tall blade front sight for it. Probably will not look like the original sight which was probably not very tall. You can calculate how much the front sight has to be raised, but with a given load. Calculate the number of inches in 100 yards. Measure the distance between the front and rear sights in inches. Divide that figure into 100 yds(in inches).
Measure how many inches the bullets strike above the exact aim point. Divide that number by the results of dividing the sight spaceing into 100 yds, prevouisly figured. Basically you are gonna get probably a fraction of an inch which is how much your front sight is short. Add height of front sight as it is now to get total height needed. Basically you can diagram that by imagining a straight line from your rear sight to the front sight, and on to the aim point. Then imagine a line from your rear sight to the actual impact point. This forms an angle and the concept is just basic geometry. Works for windage too.
