Your Colt 6920 should be fine with the 6.5 Grendel. Precision Firearms, Craddock Precision turn out quality barrels using various blanks of the buyers choice (Bartlein, Douglas, Lilja Criterion ect). You can order a 6.5 Grendel barrel directly from Lilja or other manufacturers. Brownells house brand barrels are currently made by Faxon but they also sell Criterion 6.5 Grendel barrels. The 18 Brownells barrel weighs 2 pounds one ounce and are in stock. The 18 or the 20 Brownells/Faxon are worth considering since Brownells has a good reputation for customer service.
The Group Buy 6.5 Grendel barrels sold by BFT at SixFive Arms and manufactured by Green Mountain are getting good reviews. Barrels are on order from Green Mountain and are really good barrels for the money. I have two Faxon Group Buy barrels (16 & 18) and a 12 Green Mountain Group Buy barrel. Ive been very satisfied with my Group Buy barrels.
https://www.sixfivearms.com/
The Group Buy 6.5 Grendel barrels sold by BFT at SixFive Arms and manufactured by Green Mountain are getting good reviews. Barrels are on order from Green Mountain and are really good barrels for the money. I have two Faxon Group Buy barrels (16 & 18) and a 12 Green Mountain Group Buy barrel. Ive been very satisfied with my Group Buy barrels.
https://www.sixfivearms.com/