This is pretty interesting. A 22-250 in a mostly AR-15 sized lower. AR-15 Specifications Receiver Material 7075 T6 Aluminum Forged Receivers Machined By Olympic Arms Receiver Finish Black Matte Anodized Receivers, Parkerized Steel Parts Action Gas Operated Semi-automatic Action Upper Type Flat top w/ picatinny rails Front Sight Gas block w/ picatinny rails Handguard Predator FIRSH Barrel 24” Heavy match grade bull barrel, 416 stainless steel Chambering .22-250 REM;.223 WSSM, .243 WSSM, .25 WSSM, .300 OSSM Bore Long-life non-chromed bore Twist Rate .22-250 REM (1x14) .223 WSSM (1x14) .243 WSSM (1x10) .25 WSSM (1x10) .300 OSSM (1x12) Muzzle Crown Stock ACE FX Skeleton Stock The Only AR-15 that can be chambered in .22-250 Rem. The UMAR utilizes an extended length magazine well to accomodate the UMAR magazine allowing shooters the ability to utilize longer COL loads. This is especially applicable to the WSSM cartridges when wanting to load heavier bullets. This proprietary lower design still accepts MIL Spec upper receivers or various calibers and their appropriate magazines. The UMAR comes with one 5 round caliber specific custom magazine that will either fit the .22-250 or the WSSM/OSSM cartridge 24" SS Bull Barrel* Fluting available for additional cost Picatinny flat-top upper Olympic Arms Predator Style handguard A2 buttstock Optional ACE skeleton stock (shown in picture) Your choice of side-sling mount or bi-pod mount 5 round billet aluminum magazine *Bull barrel standard on the UMAR for the WSSM & OSSM cartridges are 416 SS precision broach-cut barrels. All .22-250 caliber UMAR rifles use 416 SS button rifled barrels.