A photo or two would certainly help one understand your Merkel's "design to mount scope".
This is a article I posted on 3 February 2023 that received 7 pages of comments. It contains photos of several different options for mount reflex "red dot" sights on doubles including Merkels.
Red Dot and RMR Sights for Dangerous Game Rifles
Above photos are Trijocon SRO on Heym 88B
I have been contributing information concerning Red Dot and RMR Sights for Dangerous Game Rifles on a couple of other threads that some AH members may have missed. I figure that this information warrants its own thread, so here you go!
Warning, this isn’t an article about every sight available. I am not a professional writer, as evident my often lack of editing! Nor do any manufacturers send me stuff to use so that I will give them free advertising. Rather, this is...
I recommend you read the entire thread for many members posted different opinions and solutions. You should select the best for your situation.
JJ Perodeau https://jjperodeau.com/ can mill your double rifle’s rib to accept these mounts.
Trijicon SRO mounted on a Heym 88B with Trijicon RM 57 quick release mount
View attachment 707939
Within the aforementioned article,
@kevin Peacock contributed this,
"The base is a Henneberger HMS uni-rail 6-10mm for Trijicon. You have to mill out the base groove from 10mm to 12mm and drill and tal two small attachment holes on the rib. Very neat and tidy, and very strong and stable."
View attachment 707940
I mount my Reflex sights forward which affords me quicker target acquisition. Others mount closer to the standing breach like Kevin did above. That affords a wider field of view through the window on the Reflex.
Here is a link to order a Henneberger mount,
Henneberger HMS Trijicon RMR Mount for UNI 6-10 mm Rail
www.optics-trade.eu
Desert Dog Outdoors provides a common sense video of this subject
Read the full 7-page thread, use the search function to find other red dot posts, and watch the Desert Dog video above. There are lots of answers. In hindsight, the Henneberger mount is the easiest and provides a low profile sighting plain.
Here's more info with photos...
Since posting the above article and photos, I've followed
@Kevin Peacocke in using a Hennenberger mount for my Trusty Heym in Mighty .458 Win.
I haven't shot with this Aimpoint H1 sight but I plan to. Aimpoint are much better target sights than are my Trijicon SROs because Aimpoints "track". That means if the sight adjustment clicks are 1 MOA or a hair over an inch at 100 yards, to move the Point of Impact (POI) 1 inch at 50 yards, that shoudl be 2 clicks. Aimpoint = Yes! Trijicon = not quite... Tracking is actually move the POI Up X and Over Y, shoot for POI, then reverse the adjustment and shoot. If the POI moved and returned to original POI, the sight or scope tracks.
View attachment 707996
View attachment 707997
This is the bottom of a Henneberger mount with the raceway milled to fit my Heym's rib.
View attachment 707998
This is a Trijicon SRO ready to mount for the Henneberger Trijicon-Specific mount that is installed on my Heym 88B. The Aimpoint and Trijicon mounts from Henneberger are different.
View attachment 707999
Trijicon SRO on Henneberger mount on Heym 88B
View attachment 708000
View attachment 708001
I never go to the field without a spare... Marine Corps maintainer logic is 100% backup on single point of failure critical components. That is the maintenance version of Combat Arms 3 to 1 Combat Overmatch.
Since I have a spare SRO on RM57 Quick Release mount, why not? My sighting dope is written on rough surface painter tape. These sights come off and reinstall with little shift of POI (zero).
View attachment 708002
View attachment 708003
Bottom of RM57 mount.
View attachment 708004
Finally, in Africa no matter how long the tracking or stalk, I carry my own rifle. I do however take a nice backpack as a gift to a lucky tracker who I ask to carry a few essentials for me. For my upcoming Tuskless hunt, that will include my spare SRO and a handy-dandy Torx wrench!
View attachment 708005
