Hi! My first post here.

I got a new Bushmaster  M4 style carbine before the ban expired and am having fun buying the accessories for it thanks to a lot of help with information from this forum. A GREAT place for info!

Question: How tight should the fit up be between the upper and lower receiver? Mine has a very slight wobble and it has been nearly two decades since my Army Guard Mechanized Infantry days to remember how a "typical" M-16 fits together. I know generally military style weapons have tolerances built in for the abusive environment they see. Is a little wobble normal?

Even my match HBAR wobbles a little.  It is not a problem, the sights are affixed to the barrel, not the lower receiver.   It's alarming but harmless to accuracy or functioning.  Ops

Accuwedge will fix that.  I had a very slight wobble at the range and my buddy handed me one of those to install, and let me tell you, it is tight now!!!

Quoted: Accuwedge will fix that.  I had a very slight wobble at the range and my buddy handed me one of those to install, and let me tell you, it is tight now!!!

+1

This is an inherent problem in the AR design and the accuwedge was specifically made to address this problem.

You can get one for $2 at RGUNS here

you can go accuwedge.  that's true.  but a dab of epoxy on the rear lug of the upper will do the same thing and you won't loose it when cleaning your rifle.
i don't have to tell you to let it dry before assembling the upper and lower and use a file to remove the excess.