Please select the rear sight and bolt picture below:K31 has an aluminum bolt handle and the rear sight is right in front of the receiver:For regular scopes: Gen 4 Swiss K31 NDT Scope MountFor scout (LER) scopes: Swiss K31 Ultra Low-Profile NDT Scout Mount1911 Long Rifle or K11 Carbine have plastic bolt handle and the distance between the rear sight and the receiver is longer than K31: