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The UMAR rifle chambered in 300 OSSM (Olympic Super Short Magnum)

Availability: Available (built to order)



The Only AR-15 that can be chambered in 300 Olympic Super Short Magnum

The following features are used in addtion to standard
features on the UMAR lower receiver:

1. Modified UMAR AR-15 lower receiver magazine well. Designed specifically for the UMAR magazines to accept the longer loads of the 300 OSSM, as well as other caliber likes the venerable .22-250.

2. Threaded bolt catch hole: designed for a quick and easy change of your bolt catch between standard 5.56 magazines and the UMAR magazines, (Which use different bolt catches). Swap back and forth in seconds!

3. All modified UMAR lower receivers can also readily accept every standard AR-15 upper and caliber option. The UMAR lower is applicable to all AR-15 calibers from .22 LR and 5.56 NATO, to the WSSM and .22-250 calibers. Just swap the upper, the magazine and the bolt catch (if needed).

4. UMAR magazines come in two vatieties:
.22-250 or WSSM/OSSM


Standard Features include:

  • Your choice of side-sling mount or bi-pod mount
  • 5 round billet aluminum magazine (Caliber specific)
Upper type: Forged flat top w/ picatinny rails
Front sight:  Gas block w/ picatinny rails
Handguard: Free floating aluminum tube w/ rails
Barrel:  24” Bull, button rifled, 416 Stainless steel
Chambering: .300 OSSM
Bore:  Long-life non-chromed bore
Twist rate: 1x12
Muzzle: Crown
Stock: A2 w/ trapdoor
Length/Weight:  42.5” / 9.41 lbs

Additional Information


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Olympic Arms, Inc. is not affiliated with the IOC/USOC or any other Olympic sports organization.