This is an odd question because it is in regards to an LPA ghost ring sight set up.  There are TWO different height tritium front sights that I can choose, both differ quite a bit from my factory non tritium front sight.  Neither front sights are adjustable and you are stuck with their stock heights and have to make all elevation adjustments with the rear.  So either way, my zero is going to be off after installation so have to figure out by how much.  

I am trying to figure out how much I would have to adjust the LPA's rear sight elevation to get close to the zero I was at before the front sight post swap (Benelli M2).  
The stock front sight post height is .032 inches from its base to top.  
The shorter tritium sight is .024 inches from base to top,
and the taller tritium sight is .037 inches from base to top.  

So..... .05" difference for the taller sight from factory, and .07" difference for the shorter sight from factory sight.
Even though there will be more of an adjustment different between the stock sight and the shorter tritium sight, my preference would be to go with that set up since it has better protection from the front sight post wings where as the top of the taller sight is pretty much flush with the protective wings (so less protected).  

Assuming an 18.5" barrel and 23" sight radius from rear peep to front post, what type of MOA differences are we looking at for each sight?  ~6"-7" distance from eye to rear sight if that matters.

I'd like to preemptively adjust my rear so that the zero is as close as possible to what the factory was before fine tuning at the range.  The annoying thing about the LPA ghost ring sights, is that they are set up for 1/3 MOA elevation adjustments, so counter acting a POI change at 50 yards or less is a PITA!

Thanks!

Brownell’s catalog had the formula for assessing the sight height requirement for long guns.  I looked on Brownell’s sight and couldn’t find the info.  Dawson Precision has a formula for handguns which might work for shotguns.   You could count the number of clicks in the rear sight to get the total number of MOA of movement (30 clicks at 1/3 MOA would be 10 MOA of adjustment).    Remember the front sight moves opposite the way the bullet impacts the target.   A shorter front sight raises point of impact.   A taller front sight lowers point of impact on target.   Another element is the height of the sight over the center of the bore.   I don’t know if a large ghost ring rear sight would permit me to get a small group on target at 50 yards with slugs.

I figure a ghost ring sight smooth bore shotgun is about a 4 MOA or greater weapon.   A fully rifled barrel with good ammo can do better but not sure about a Benelli M2.   With improved cylinder I’d feel lucky to get 3 MOA at 100 yards with my 1014 with ghost ring sights and slugs.

In a shotgun I would rather have the shotgun shoot high of point of aim.  If the weapon impacts low then your covering the target or aiming over the target with your front sight when trying to raise the point of impact.    Many battles rifles use a belly hold at close range and have sights more dead on at 200-400 yard zero depending on the cartridge.    


If I was unsure I’d order the taller front sight for a shotgun which would lower your point of impact on a fixed rear sight or no rear sight weapon..    I’d count the number of clicks and determine where the current sight is zeroed for elevation on an adjustable rear sight.    More than likely the rear sight is mid way in the total adjustment but counting the clicks is not difficult and can help finalize your decision.   Remember lowering the rear sight lowers the point of impact.  Raising the rear sight raises the point of impact.


Honestly I think either height front sight is going to be on target enough at 20-30 yards to give an indication to make adjustments to be on target regardless of your selected zero range (50, 100 or whatever distance).    I’ve seen bent shotgun barrels where we needed to bend them in a tree fork to get the sights to zero.   I don’t know if you will have any luck trying to do the math and get the holds figured out.   Shotguns and ammo are really different and normally you just have to shoot them and then go from there.    I’ve probably zeroed twenty five to thirty shotguns so I’m no expert but I’ve been down that road before.



https://dawsonprecision.com/sight-calculator/

Thank you for the link, it doesn't really help me though and is more of a shopping aid than an accurate equation or formula.

I have the shotgun zero'd now with the factory sights.  It is pretty much dead on with how I have it sighted in now.  Had to ramp the rear sight up a bit, but am curious just how off my zero is going to be now and how many clicks would be required subsequently.

Ditto.  I prefer to float a target on top of the bead with a shotgun.

Which is again why my preference is leaning towards the shorter sight.  However I don't want it to be too far off (IE a foot high).  Would like to compensate for the height difference as much as I can.

(1.047/3600)*radius

So 23" would be 0.0067" per MOA. A 0.05" and 0.07" difference would be 7.5 and 10.5 MOA difference.

Wow, thank you so much!  So around 30 clicks at 1/3rd MOA adjustments per click to get back to where I was with the lower sight from the factory sight.