Got two new RRA in, both uppers and lowers extremely well fitted. One has tight fitting handguards, the other is loose and rattles.

Should I return the second one to RRA or is there an easy fix?

I assume that you mean the handguards are loose fitting against the metal rings on each end that hold them to the barrel.  I had one that fit loose a while back.  I had to put three layers of black electrical tape over the end that goes under the metal ring.  There may be some fancier way to adjust this, but this quick fix of basically making a shim has worked for me.  I was careful in my placement of the black tape, so that it isn't visible once the hanguards are on.

In another thread, someone said that they used the BLACK High Temp RTV silicon form-a-gasket to tighten up their forearms. Just filled the grooves with the RTV and put it back together. When it set up they trimmed the excess with a razor blade. They also said that if you don't like it the RTV just peels right off all surfaces.

I haven't tried it yet, but I will pretty soon. I have one handguard that really bugs me with the rattle and wobble.

The fit of the handguards can be effected by several factors.

[b]If they're loose, rattling.[/b]

Too great of a distance between the handguard cap and the barrel nut. Mis-located FSB, handguards short, incorrect length between FSB and barrel extension shoulder, etc.  The length of the threads on the upper receiver can also be a factor here.

Missing detents (small raised semi cicular bumps) in the groove for the teeth of the barrel nut.

Mis-timed barrel nut with handguards forced to fit.

Dummy gas tube missing on non gas op uppers.

[b]If they're tight, hard to remove.[/b]

Too little distance between the handguard cap and the barrel nut. Mis-located FSB, handguards long, incorrect length between FSB and barrel extension shoulder, etc. The length of the threads on the upper receiver can also be a factor here.

Mis-timed barrel nut with handguards forced to fit.

Groove in handguard for teeth of barrel nut too narrow.

Ok..........while I dont have any rattle on my RRA handguards...........I do have some 'rotational' movement. I would say 1/8" maybe the handguard has this 'side-to-side slop'.

I really dont know how else to explain it. It doesnt have any rattle and there is no
front-to-back play..........just this every so slight back and forth rotational play.

Should this little bit of play be expected out of an M4 handguard? Or is there a way I can tighten things up for literally NO movement, play, or slop?

Rifle:
RRA M4 Tactical Entry LE w/ 6 Position Stock

LPD,

Take the handguards off and see if the detents are present in the groove for the teeth of the barrel nut. Assuming the gas tube is present the hole for the gas tube in the handguard cap may be overly large.