Denny at Global Tactical Solutions is now offering his excellent Ion Bond Super Duty bolts separately from the carrier. Previously, they had to be purchased as a complete bolt/carrier group (BCG). Now they are available to those who already have a good carrier on hand.
These bolts are everything a bolt should be (shot peened extractor with improved spring and correct insert and MP tested) but they also have the excellent upgrade of being Ion Bonded. The Ion Bond coating is self-lubricating (you still need lube), very hard and wear resistant, and it cleans very easily.
The bolts are top notch and the coating is amazing. I have been using one of the Super Duty BCGs in my range pig (the rifle that gets burnt up at the range more often than all my others) for 3 years. It has just short of 4000 trouble free rounds on it, many of which have come during higher volume training. This is great gear.