I bought a Armalight lower parts kit for my build and when I assembled it the selector switch is a little loose and not quite precise. Do I need to get a different selector switch or jus try to adjust it ? it just feels a little loose. Any suggestions? Thanks.

Did you use the correct detent and spring? Is it installed correctly with the spring going into the hole in the pistol grip?

I will check but everything else fits fine could the detent be changeable with another one? which one ? Thanks

I took pistol grip off and checked spring and detent both correct and reassembled them and tightened up grip MIAD and it seemed to be a little better still a little play back and forth side to side unlike other AR. hmmmmmmm???

Sometimes the detent depressions are cut a little wider and/or deeper on a given switch and this will give you a sloppy  feeling.  I've even seen it on Colt built M16 parts.  In some other cases the hole in the lower for the detent itself is a couple of thousanths on the big side, in which case you're going to have a bit of slop no matter what you do.

Just part of thr joy of owning more than one AR are the variations you encounter between different pieces