I have a new rifle.  Built by a quality shop (its a Polish kit, all matching, etc..).  Everything is great but then I noticed I can move the lower hand guard retainer back and forth or if you will, towards and away from the receiver. There isn't any rotating movement just up and down the barrel. On all my other rifles I have to beat the front retainer out of position with a little hammer once the locking level is up.  It can be moved maybe a good 1/8".  So I put the hand guard "into" the receiver, slide the retainer down tight up against it and push down the locking lever but then either by just pushing on the hand guard or grabbing the retainer itself I can move it toward the muzzle easily the 1/8".  It doesn't move so much that the hand guard "falls out".  I use the sling loop of course so it will be going back and forth.  I can't see anything out of the ordinary when inspecting it.  

Any thought?

Thanks in advance.

I used to shim loose wood HGs with a little bit of cardboard. I'm sure that would tighten things up.

Not sure if you are serious ….

The problem isn't the hand guard its the retainer.

Is the slot on the bbl where the HG locks oversized? If you cut the cardboard to fit in your retainer it'll force the retainer FWD when you install the HG. If the retainer is to far FWD and past the upper HG retainer, you can weld and recut the slot. I used JB Weld on a Maddi that had the retainer too far FWD. Filled in the slot on the bbl and recut it. It still holding after 8 plus years. JB is good to ~600* so as long as you don't do too many mag dumps in a row...

Take it back to whoever built it. The lower hand guard should be securely locked by the retainer.