The SPR Mod 1 is forged, one-piece upper receiver/rail system with exclusive detachable side and bottom rails. ArmaLite takes that versatility even further. Each SPR Mod 1 comes with three extra rails standard, at no extra cost. We give you a 1913 rail with quick detchable sling swivel hole. Each rifle comes with a low insert for when you need a bare rail with a low profile. There's also a plain insert with a quick detach sling swivel hole. Changing your rails,your add-ons, and your SPR Mod 1 is as easy as turning a torque wrench. Ingenious versatility isn't the only reason you'll want an SPR Mod 1. Its one-piece construction offers you a continuous optic platform (COP). There's no gap to bridge between receiver and upper rail when you're installing your scope or sights. This one-piece construction also gives the sighting platform extra rigidity. It's a good, strong backbone. That means your sights will stay zeroed in the most trying conditions.