The Grendel is my favorite AR 15 caliber. I shoot my custom 20 inch 6.5 grendel to 1000 yards with success. It will hold 1 moa at 1K. With that said. I decided to build a Bench rest 6.5 Grendel. This is where the round lost its luster. I put 700 rounds through the barrel testing loads and bullets. If there is a powder I tried it with 120-130 grain bullets from most manufacturers. In my custom chamber I could push it to 2950 fps with no pressure. But I could not pysically fit anymore powder in case to go further. ( This was bolt gun with 32 inch barrel I don't recommend trying in gas
. What I found with accuracy was the round likes 2500 fps-2750fps. It did not like going above 2850 with accuracy. (1.5 inch group avg) I do believe this is due to case design and case capacity's. My 6.5x47 likes 2900 fps with same bullets. I pulled barrel and rechambered it and never looked back. I still love my Grendel gas guns though.