When I zeroed in my new AR, the rear site ened up almost all the way to the left.  There was no wind and we were shooting at 25yrds.

Should I do anything about that?  

As long as rifle is zeroed, wouldn't worry about it, my ARMS #40 BUIS, is way right, but rounds fall on-target so it's no big deal.

Mike

PS - other than zeroing my rifle at 50 yards insead of 25, this might be of some use:

[red]Gunsmithing TIPS from Chris: Barreling Uppers...
Installing a barrel is really pretty simple. Solving some of the problems you can run into isn't. Probably the most common problem is excessive windage present after the installation. The rear sight will be cranked all the way to one side. This is one time the manual doesn't help much, most military armorer learn this trick early. Here's how to fix it. Clamp the barrel in a vise, using barrel blocks. Line up the front sight carefully on a vertical line, just like the book says. First tighten up the barrel nut - hand tight, not torque to prevent damage to receiver. Now, look at your receiver. Chances are it's leaning off to one side -when compared to the front sight. Using a non-marring hammer, hit the side of the carrying handle, as near to the front as you can. This will rotate the receiver slightly to one side or the other. Here's the trick, hit on the side that the rear aperture is furthest away from. In other words, try to move the receiver towards the rear sight. Be careful, you don't have to kill it, just a firm tap will usually do the trick. If the barrel is straight, aligning the receiver forging with the front sight forging will usually put the windage adjustment right in the middle, and it takes about a minute to do it. Simple! One other trick we should mention is for when you are torquing on a barrel nut and everything locks up. A squeaking noise, then it's like it's welded right there. The surest way to break something is to keep trying to loosen it. This trick is so simple, we couldn't believe it. Put the whole assembly in the freezer, and leave it overnight. This gets some differential expansion working for you. Pull it out the next day, and it will almost always come loose. We recommend using an action block, like the one we sell, and clamping on the receiver to prevent breaking the index pin when doing this. A really good wrench, like the heavy duty one we sell, will prevent ruining the barrel nut.[/red]