The Mag Tactical Systems magnesium AR-15 lower is about 2oz lighter than one of my typical forged aluminum lowers. I know that does not sound like much and it is not, but if you can shave off a few ounces here and there on your AR15, the end result will be a lighter more maneuverable rifle. In my particular case I was wanting a light weight hunting rifle in the Modern Sporting Rifle configuration (MSR). So on my shopping list of parts for the 300 blackout build I went with the magnesium lower over the polymer lower. The polymer lowers just feel cheap to me even though they are lighter. The only issue I had assembling my MAG lower to the upper was the need to remove some material on the lower near the rear take down pin. This was not painful but it is nerve racking when you file on your gun. However, the end result was a perfectly fitted upper and lower with no movement between the two. Below is some comparison photos of the magnesium lower compared to a polymer, forged aluminum and billet aluminum receivers. The differences are subtle, but differences none the less. The most striking is the extra long trigger and hammer pins that came with the lower. I hear that the lower needed to be beefed up some at the pin holes. The end result is a hump where the pins pass through.