One really important consideration that you need to think about when buying a red dot sight is how to attach it to your weapon.
Does your long gun have a rail or do you need to install one? If you are using a current production M4-type carbine, most red dots that have built-in mounts will fit its Picatinny flattop right out of the box. If you are using an older AR15/M16 with an attached carry handle you will need a mount to fit in the handle or a scout mount. I suggest the carry handle scout mount to ensure that you have enough vertical adjustment in the sight and to ensure that you have a solid cheek weld on the long gun's stock.
One thing I have found gun owners tend to overlook when buying a red dot sight for use on a long gun-especially an AR-style rifle-is the front sight. Unless your AR has a fold down front sight, you'll want to ensure the dot of the sight is not centered in the back of the AR's sight base. So you may need to install a riser base. You can buy one from Brownell's; it will set you back about $20.
Since we are talking about bases and mounts for a red dot, I should tell you that some of the sights come with weapon-specific mounts and some red dots are sold only as the sight. It may sound ridiculous that a sight would not have a base, but there are numerous manufacturers who make nothing but mounting assemblies to meet the operator's specifications for the design of the firearm you are installing the red dot on.
Rugged and Reliable
Over the last decade and a half, I have had the chance to use most of the red dot sights on the market. Both the holographic and tube-type sights have proven themselves to be capable of surviving the rigors of combat.
Red dot sights have improved most users' hit probability; they allow shooters to make faster, more accurate follow-up shots, and, for those of us who are over 40 and have less than eagle eyes, these electronic marvels are far easier to see than a post front sight. I have been using the same Tasco ProPoint for the last 12 years; my EoTech has been perched on my M4 for the last four years. It has survived trips to the SIGArms Academy and Blackwater and all the abuse that week-long carbine classes can inflict on equipment. My shooting partner is a cop, and he has had an Aimpoint Comp 2 on his patrol M4 for several years, and it has survived daily use, including the in and out of the cruiser and all the associated shock of being a duty tool.
I have seen Bushnell Holosights and C More sights that have weathered years of abuse from competitive shooting. Our troops in Iraq and Afghanistan swear by the Trijicon ACOGs, Leupold CQTs, and Burris Tactical Speed Dots.
Finally, red dot sights are very reliable, but batteries fail, electronics break, lenses get dirty or get broken. Take the time to keep your long gun sighted in with its iron sights.
RED DOT SIGHTS