Go to your steam directory:

steam\steamapps\common\Hunt Showdown\user\profiles\default\attributes

for me it's all installed on drive C:\Program Files (x86)

now open the "attributes"-file with notepad.

now press Ctrl+F (Search) and search for your in-game nickname.

you will see something like this:

<Attr value="YOURNAMEHERE" name="MissionBagPlayer_0_1_blood_line_name"/>

<Attr value="false" name="MissionBagPlayer_0_1_hadWellspring"/>

<Attr value="false" name="MissionBagPlayer_0_1_hadbounty"/>

<Attr value="0" name="MissionBagPlayer_0_1_killedbyme"/>

<Attr value="0" name="MissionBagPlayer_0_1_killedme"/>

<Attr value="3237" name="MissionBagPlayer_0_1_mmr"/>

the number highlighted at the bottom is your current MMR.

it will take some time to update after every match and doesn't instantly change upon fragging or dying.