You might want to try if VSync affects it. Launch "Configure Running with rifles" and turn VSync off. While it is ideal to play with VSync on, give it a try.
Another thing, this could be a long shot, you could also check the contents of your stored settings file, the file is at C:\ProgramData\Running with rifles\settings.xml.
I've got them like this:
Code:
<settings>
<shadows value="1" />
<post_processing value="1" />
<mouse sensitivity="0.255640" />
<aim_helper value="1" />
<player_marker value="1" />
<keyboard_controls>
<control0 value="17" />
<control1 value="31" />
<control2 value="30" />
<control3 value="32" />
<control5 value="19" />
<control6 value="34" />
<control7 value="35" />
<control8 value="47" />
<control9 value="57" />
<control10 value="29" />
<control11 value="46" />
<control12 value="42" />
<control13 value="33" />
<control14 value="20" />
<control16 value="28" />
<control19 value="48" />
</keyboard_controls>
<mouse_controls>
<control4 value="0" />
<control15 value="1" />
</mouse_controls>
<map_resource_location>media/maps/empty</map_resource_location>
<clean_up_bodies_threshold value="0" />
<score_notification value="1" />
<bullet_trails value="1.000000" />
<isoline_occurrence value="0.239433" />
<isoline_intensity value="0.066283" />
<camera_smooth_factor value="0.100000" />
<aim_helper_speed value="0.015000" />
</settings>
I'd especially check the last ones that camera smooth factor value is 0.1 and aim helper speed is 0.015. They're known to have caused some issues for players who played the game a long time ago and these new settings didn't end up with meaningful values.