Chest rig?

Have a look at Simply Rugged here in Prescott.  If you email owner Rob he will likely have something for you.

I own several.  Good stuff from a real gun guy.

I have the same gun. For over 40 years, I have used the old western style holster comprised of the dedicated belt with attached holster. It was all I could find at the time. I have used it extensively for hunting over the years.

A few years ago I purchased two types of chest holsters for other guns. One was for a freedom arms .454 casull by Diamond D out of Alaska. The other was from the above mentioned Simply Rugged for 6" Ruger Redhawk plus a belt holster for the Desert Eagle .50 AE with the "Chesty Puller" option. All of them were top notch and would highly recommend.

With the 10 1/2" barrel, I would think drawing it out might be a little difficult depending on how the user has it angled.

IIRC, correctly the Diamond D has two options for the chest carry as in the way the gun fits across the chest or kind of a cross draw under the arm.

It might be worth it to contact Simply Rugged as the previous poster suggested to see if they can offer something to accommodate that length of barrel.

Just thinking out of the box for the moment; have you considered a saddle mounted holster of some sort? While riding, the gun goes on the saddle mount. When you dismount, you put in your current set up.

I haven't owned horses in many many years and never thought about this issue. I love my big 10" as it doubles as a mid range gun almost like a carbine. I hunted deer and hogs with it and had no problem taking 50 yard shots ethically. Hunting the swamps and dense vegetation made it a great choice for me.

Keep us informed on what you decide to do.

Found a video with the Diamond D chest holster that might give you some perspective.

Video

So are you wanting a crossdraw slim jim?  What size belt are you going to wear it on?  For a 10 1/2 inch Blackhawk.

For me longer barrels (longer than 5" or so) I either used a cross draw, chest rig or western styled drop leg holster. Trying to yank even a 7 1/2" barreled revolver from a holster high up on my belt didn't work out.

I don't ride a horse but if I did I think any belt holster would be less usable than a chest type rig.

I carry 3 3/4" revolvers cross draw while bank fishing here in Florida, and since I cast lefty and shoot with my right hand I could dispatch a gator without even dropping my fishing rod :-)