awshucks......Have been selling Excaliburs and a few other brands(including Gold Tip arrows and bolts) longer than I might want to say...Carbon inserts have been around about 15 years, taking weight off the front end stiffens the shaft(mostly for archery applications) The Lazer2 bolt accepts 2117 inserts and if you look around you cay still find a few....I do not like the insert that comes with the Lazer2 bolts(they weigh almost 100g) so I use either the carbon or a regular 2117 insert.....