CASV-M Flip-up Front Sight (part # CAS-FS). When using a low-profile gas block or a gas block without iron sights, the CASV-M will accept a specially designed flip-up front iron sight that mounts to the upper forward portion of the CASV-M chassis. This is ideal for any short barrel and/or short gas system. This front sight system comes with all mounting hardware and retails for $69.95.