For starters, I am an AK noob.  I bought a PSA AK 103 Premium.  I have owned it since last July, but only shot it once.  Got about 5 moa using tula ammo.  The muzzle device wiggles/has slop.  When I pushed in the detent and rotated it to tighten, I can get about 3/4 of the way around and it is tight, but about a 1/4 the way short of the detent.  I am concerned that the loose device does affect accuracy.  I presume that it is supposed to be tight?  What would folks advise I do?  I thought about maybe using a shim, shaving some material off the base of the device to get the extra turn or just buying another MD.
I also notice that the FN barrel is not crowned.  I do not know if this is common for AK's?
Any feedback would be appreciated.

Yup. Normal on an AK.

My 103 is exactly the same. Works great

As mentioned, thats normal.  Thats why there's a detent.  The milspec style muzzle brakes are not torqued down.  Detent keeps them timed and not spinning off on their own.

As far as 5MOA, thats tulammo for you.  Keep in mind that many other 7.62x39 ammo is also made by tulammo.  Usually you can tell because its the 122gr stuff and/or you can see the tulammo logo on the back of the box.  123gr and 124gr is probably not tulammo and should be more consistent.

Thanks everyone.