Join us on http://www.R6CHAT.com Discord and post in #techsupport with any questions. But this fix solved a lot of problems for me on Windows 10.

Force a game to run a particular version of DirectX / Direct3D
So, for example, you got this game running in DirectX 11 mode, but the game also supports DirectX 9 + DirectX 10 but there's no way to change it manually? No problem, there's a simple way to enforce a particular version of DirectX for your old Graphics Card.

1. First of all, click Windows Start button -> Settings -> Apps -> Optional Features -> Add a feature and wait for the list to load.
In case the list doesn't load in a few minutes, press CTRL + SHIFT + ESC to open the Task Manager, search for "Settings", end the task and repeat the step again.

2. Click "Graphics Tools" and select "Install", then go back using the arrow on top left of the window.
The feature will be installing, wait for the process to complete. (If you already have it installed, skip this step.)

3. Once done, press Windows Key + R to open the Run window, type in dxcpl and press Enter.

4. In the "Direct3D 10/11/12" tab, click "Edit List...", then click the "..." button and browse for the main game executable, then click "Add" and "OK". You can add any executable you want to run with the same settings.

5. Once done, you'll notice that all the settings in the window are now clickable.
Check "Device Settings" on bottom, tick "Disable Feature Level Upgrade", then choose any version you want next to "Feature level limit".
Make sure the version you're choosing is supported by the game, otherwise it won't launch. If the game gives a DirectX fatal error, you may need to use a different version. You can't force versions below 9. Rainbow Six 3 should work with Direct X 9_3 or lower I believe but I didn't try 9_2 or 9_1.

Once done, click OK and launch your game.

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Why use this?

For me, this solved some stuttering issues/minor lock up issues when I would place a waypoint or get shot at and be wounded.

Changing my CPU Affinity to have only 1 core also worked but I didn't want to have to do that every time. I run Windows 10. But on my Windows 7 PC I never had to do this. Just Windows 10 gave me some issues. Anyways, hope it helps.

Screenshot:
https://cdn.discordapp.com/attachments/331387031110549506/677266784793002015/unknown.png