I just put a 7.0 Larue rail on a LMT upper and when I hold onto the rail and wiggle the end of the barrel there is the slightest up and down play in the barrel but none side to side. This is the first time I have installed a rail and I do not know if this is normal. Cold someone please help me out.
Jeremy
Did you take the Barrel off to install the rail? If so, you probbly didn’t put it back on correctly. Have a real armour check it out. It is much safer that way. He has the right tools.
I figured it out. The gap between the upper and the lower was flexing and creating the illusion that the barrel was wiggling. Thanks for the reply above, but I
installed the rail at my gunsmiths shop under his supervision with the correct tools.
If this is the case than why ask!
Because we are all supposed to remember that the only dumb questions are the ones we don’t ask. 
What JohnnyVegas said. Oh and because local gunsmiths don’t know everything.