We think the standard A3 upper receiver is pretty good, and hard to improve on (cosmetics don't count), but there are couple of areas we always wished the manufacturer would change. It was one of these "why can't they make it like this, it'd be easier/better" that led to the URF.
URF is based on CMT's URPR-1 7075 billet upper receiver. Type 3 hard coated in black, it is an excellent basis for the two ergonomics driven changes we've always wanted:
1. Relief cuts on the section before rails start for better accessibility of a flip up BUIS's sight stalk / flip up element.
2. Relief on the top of forward assist housing. The relief cut is specifically designed for ambi charging handle users. When the user uses his right fingers to pinch and grasp the CH's right latch, the relief allows the index finger to reach down further, so the CH's right latch is positioned in the middle of his finger pad, not the tip of it, for a more secure purchase, especially if the user has gloves on. When we use our left fingers to grab the charging handle's left latch, there is nothing below the latch, but on an upper with forward assist, its housing stands in the way. The relief simply provides what room that can be spared on the FA housing so more of the user's finger can have a positive purchase.
The FA housing relief is a simple broad stroke. In retrospect, we could have made its presence less shockingly obvious. The change we made is there to work, we didn't give much thoughts to how it'd look, only that it'd create as much clearance as the FA housing can afford to give. Our design philosophy emphasizes utility, innovation and quality derived advantages, aesthetics is a super minority in this equation.
2020 production URF v2 has done away with the over pressure gas relief port. It has retained the relief that clears the LMT MARS-L lower receiver's right side bolt catch, and thus compatible with MARS-L.