This data is some I collected from listed sources or what a Friend and I got using his Magnettospeed chronograph a few years ago.
12” 6.5 Grendel chronograph results
Buffman Range video 12” PSA 6.5 Grendel Federal Berger 130 grain HOTM GMM 2073 FPS (Pro Chrony)
18” PSA Nitride 6.5 Grendel Federal 130 grain Hybrid-OTM Berger GMM 2322 FPS (Pro Chrony)
12” PSA SS with LabRadar.
123gr Hornady American Gunner bulk HPBT = 2201 FPS ave with SD of 14.7 (2" to 2.55" groups)
123gr Hornady ELD-M Black = 2265 FPS ave with SD of 13.2 (1.4 to 1.7" groups)
123gr Hornady Custom SST Factory= 2277 ave with SD of 11.8 (2.9 to 3.2" groups)
12” Faxon
Wolf steel case at 2364 Avg. SD was 9.7.
Here is a list of the tested ammo by average velocity for each barrel length.
120 Grain HP BT PPU
16" 2392
18" 2455
20" 2480
24" 2559
110 grain FMJ PPU
16" 2510
18" 2570
20" 2614
24" 2683
123 grain A-Max Hornady
12” 2265 (123 grain ELD-M)
16" 2419
18" 2464
20" 2505
24" 2568
123 Grain SST Hornady
12” 2277
16" 2430
18" 2493
20" 2511
24" 2583
Hand Load 123 Grain Nosler CC, 31.0 grains CFE223, CCI 450
16" 2449
18" 2471
20" 2526
24" 2619
100 Grain FMJ Wolf
12” 2364
16" 2507
18" 2571
20" 2615
24" 2695
Hand Load 107 Grain SMK 28.5 IMR8208XBR, CCI 41 Hornady cases.
20" 2658
24" 2729
Hornady 123 grain American Gunner
12” 2201
Here is the difference between the 18” barrel compared to the shorter 16” barrel which was slower with every load.
120 grain PPU HP BT
63 FPS difference
110 grain PPU FMJ
60 FPS difference
123 grain A-Max
45 FPS difference
123 grain SST
63 FPS difference
Hand load 123 grain Nosler CC
27 FPS difference
Wolf 100 grain FMJ Steel cased
64 FPS difference
Difference between 20” and 18” barrel 6.5 Grendel
120 grain PPU HP BT
25 FPS difference
110 grain PPU FMJ
44 FPS
123 grain A-Max
41 FPS difference
123 grain SST
18 FPS
Hand load 123 grain Nosler CC
55 FPS difference
Wolf 100 grain FMJ Steel Cased
44 FPS difference
Velocity Difference 20” compared to 24”
120 grain PPU HP BT
79 FPS difference
110 grain PPU FMJ
69 FPS Difference
123 grain A-Max
63 FPS Difference
123 grain SST
72 FPS difference
Hand load 31.0 grains CFE223 CCI 450 primer 123 grain Nosler CC
93 FPS Difference
Wolf 100 grain FMJ
80 FPS Difference
Hand Load 107 grain SMK 28.5 grains IMR8208XBR CCI 41 primers
71 FPS Difference