Len,
Older front sights mounted to a dove tail that was mounted via small screws drilled-n-tapped into the barrel,much like a two-piece scope base would be). The front sight 'tube' had a side clamping plate that would pinch the dovetail and that secured the site to the barrel. With that sort of system, if you needed the front sight higher or lower to help get your zero or position worked out, you had to purchase another dovetail block of a specific height. All the elevation adjustment from one yard line,say 100yds) to another,say 1000yds) was done using the rear sight. Think about that for a second... if the rear sight has to move up that much from a 100yd zero to a 1000yd zero,for a .308 Win), would your head position and cheek weld remain the same? Not at all. A thumbwheel cheekpiece helps some, but thats not really what it was intended for.
With a 'ladder' type front sight, there is usually some sort of base that mounts *around* the end of the barrel. Typically the barrel is turned down to a specific diameter - 0.750' is most common, but others like 0.812, 0.835, etc. are also used, but the selection of front sight bases that fit those sizes is significantly less. So, your front sight base slips over this 0.750' 'tenon' at the end of the barrel. Generally speaking, it attaches by clamping around that tenon. The base may either have an 'H' shaped tower rising from the front of it) or an 'L' shaped arm that attaches to the side. You'll see a series of notches machined either in the face of the tower, or in the side of the base where the 'L' attaches. These notches correspond to a specific number of MOA,based on some specific assumptions about sight radius, etc.), typically about 5 moa per notch,3 and 6 moa are other common values, depending on the model). For a ladder front sight, instead of cranking the front sight up and down for large changes in elevation between yard lines, you do the coarse adjustments by moving the front sight *down* and then fine tune with the rear sight. As an example, if your gun was zeroed for 100yds, and your 1000yd zero was 29-1/4 moa up, you'd loosen the part that holds the notched surfaces together and move it down six notches,30 moa) and re-tighten. Then click down 3/4 moa to 29-1/4 using the rear sight. This allows you to make very minimal changes with the rear sight, maintaining your head position for your Natural Point of Aim,NPoA) which is what the adjustable cheek piece is really for. Of course you have to keep pretty good track,write it down helps a lot) of what you adjusted where, and return the sight to zero between matches,or yard lines).
The front sight towers are somewhat delicate, and can get bent with a little abuse - some of the 'H' mount types come with a 'locator ring' that can be slipped on between them and the muzzle tenon, which is then locked in place. Afterwards, you can slide the whole front sight off and put it in a safe place,like a small Pelican box) and remount it when ready to use it again. The 'L' type bases typically allow you to just unscrew the bolt that tightens down the side plate and take the whole 'L' off for same effect.
There is a whole series of separate topics about choosing the rear aperature,I recommend a basic one from Gehmann or Centra) and the front aperature and any anti-glare tubes, spirit levels, or lenses you may choose to add. I'd highly suggest swinging on by www.long-range.com and reading through the pinned threads and archives there - those topics are covered in considerable detail over there.
HTH,
Monte
