Great scope - Vortex Diamondback 4-12x40 AO Rifle scopes

I got this for a .223/556 bolt action with a 24" med. heavy free floated barrel.I bought the gun as a target rifle only. Optics are sharp and clear all the way to 12X.Sighting in went as normal. It holds 0 with no problem. Field of view is good with no fish eye even at 12X.So why only 4 stars. Its big as in long and gives a little trouble working the bolt. Also I can not loosen the screws on it to reset zero.It would be very hard to find a better scope in 4-12 X 40 in this price range. This is my first Vortex scope ( I normally go with Nikon.), but it will not be my last.