This sounds about right, i have a t3x 6.5 creedmoor shortend to 18 inches and it shoots the 143gr precision hunter factory ammo at 2459fps average. My partners 16 inch creedmoor shoots them at 2379fps average. 40fps loss per inch of barrel. So yours at 20 inch and 2550 is right on what id expect to see.
I havent developed a load for either of these properly yet, but did do a speed ladder with the 18 inch one, got to 2630fps with a slightly compressed load of 2209 before seeing pressure signs. Going to revisit once im finished with working on loads for other rifles.
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