Colorado- check out http://www.newenglandcustomgun.com for a 'new' Express sight for your double. I'd suggest the single leaf sight that should be easily dovetailed into the rib. That will give a standing point-blank sight plus a flip-up leaf for 150yards. Your present loading should give full use of it's second blade. I filed the point-blank sight low and straight, rather than sloping, for a better sight picture. With a small bead on the front, there is non better.
: Once filed in and with that bead up front and a bit of practise, you'll come to love the wide "V" rear sight. It is an accurate sight for all ranges, not only a close range sight as some who couldn't have used them much like to proclaim.
: Fast for close range 'charging' animals it is, but also very accurate at distance. The bead settles in the shallow "V" perfectly, accurately and just wants to sit there with no windage problems as with "U" or "V" notches.
; It became my preferred sight for the 14 bore ML rifle, capable of shooting at close as the rifle and shooter can muster.
: Once at the site, click on rear sights, then Express, then scroll down the page to the single leaf, click on 'purchase' and it's picture will come up. While I used the 3 leaf sight for a 100, 150, 200 and 300 meter ranges, the single leaf should give 100 and 150yd sighting, perfect for your double rifle. Note the final shape of my 'standing' sight, the low one and the 150yd sight. I rarely used the longer range leafs, except at rendezvous for gong targets, so they were never "V'"d. My front sight was a 1/16" tapered brass rod, set low and soldered to an iron base, typical of muzzleloading English front sights. With little elevation needed, nor recommended, the ball travelled very close to the lineof sight, right out to 120yards, being no more than 1-1/2" above nor below the line of sight to that range. Your 180gr. charge should give that to you as well.
; A cheaper standing and single leaf sight can be found in the MISC link, rather than the express link. As it is alread stright, less filingis necessary, and the shallow "V" can easily be filed in. It appears this one might fit a standard dovetail. Good luck!
: ps - I should note that with a light, 3 dram load, my sights then zero'd at 65yds. 100yds, 150yds, and 250yards. Increasing the powder charge, merely made the rifle shoot further, giving very little additional elevation to the ball, just as Forsyth said. This is due to the low mounting of the front sight and relatively low rear sight. With high set sights, there is a greatly increasd elevation given the ball.
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