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+--- Thread: Optimal Barrel Length (/showthread.php?tid=17214)
Optimal Barrel Length - For Gallantry - 10-10-2018
I built my Grendel about a year back with a 20" Shilen barrel. While accuracy is outstanding, my velocity numbers over my Magneto Speed are well short of what I had hoped for. I see most of the book data was derived from a 24" tube and while browsing around I see that Satern offers a 28" barrel. I'm wondering if anyone has any firsthand experience with such a long barrel in this chambering and some real-world velocity numbers. Threads on other sites are all over the map-some saying that one may realize about a 60 FPS gain over a 24" barrel while others say you'll actually lose velocity. I understand the 28" is A LOT of barrel but the primary use for this gun is banging steel at long range and punching paper. Thanks in advance.
Optimal Barrel Length - grayfox - 10-10-2018
When you say your "velocity numbers... are well short" what kinds of MV are you getting for which bullet/powder/primer/brass loads? What distance are you looking for, at what elevation ASL?
I'm not a long-barrel shooter, but for a small-case style cartridge like the Grendel, you might get no real increase or lose MV after 24-26"...
Others with more long-barrel experience might chime in.
Optimal Barrel Length - VASCAR2 - 10-10-2018
There is a web site for velocity prediction plus a graph that has been posted on the forum showing the velocity trends for various 6.5 Grendel length barrels. Generally once you get past 24 with the 6.5 Grendel the velocity increase per inch is pretty small. Bwaites has a 28 6.5 Grendel if I remember correctly and maybe he or another member will post their chronograph results. From the results below going from a 20 to 24 with 123 grain A-Max yeilds a 63 FPS increase or about 15 FPS per inch. With shorter barrels the increase in velocity loss per inch is more noticeable on barrels below 20. With the 6.5 Grendel small case capacity the drag/friction from the barrel degrades some of the velocity from longer barrels.
I copied my chronograph results which I previously posted.
This question comes up fairly frequently so a couple years ago a Friend and I chronographed 4 different 6.5 Grendel AR-15s. The temperature was approximately 70 degrees and we used a Magnetto speed chronograph. We chronographed several loads in a 16 J&T Dist/Double Star 1:9 twist CMV, 18 1:8 twist SS Grendel II Satern/Liberty, 20 Shilen SS 1:9 twist and a 24 AA 1:9 twist CMV. Below are the results. These results were obtained prior to PPU recalling their 6.5 Grendel ammo. All ammo tested was out of the same lot to help in getting consistent comparison.
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
16" 2419
18" 2464
20" 2505
24" 2568
123 Grain SST Hornady
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
16" 2507
18" 2571
20" 2615
24" 2695
Hand Load 107 Grain SMK 28.5 IMR8208XBR, CCI 41 Hornady cases.
20" 2658
24" 2729
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
Link to velocity calculator site.
http://shootersnotes.com/Vel65Gren.php
Optimal Barrel Length - biodsl - 10-10-2018
Forum user bwaites has a 28" barrel. This will get you started
http://www.65grendel.com/forum/showthread.php?17575-would-the-Grendel-benefit-from-a-28-quot-barrel&highlight=barrel
Optimal Barrel Length - For Gallantry - 10-10-2018
grayfox Wrote:When you say your "velocity numbers... are well short" what kinds of MV are you getting for which bullet/powder/primer/brass loads?
2245 FPS from a 120 grain TTSX over 27.0 grains of RL15 in Lapua brass...book velocities are over 2500 FPS
Optimal Barrel Length - VASCAR2 - 10-10-2018
Here is the velocity calculator graph.
![[Image: 31349786348_1458572e34_z.jpg]](https://farm2.staticflickr.com/1909/31349786348_1458572e34_z.jpg)
49B5F7E7-B98B-4324-A30A-66BACBA3A740
Optimal Barrel Length - Bigs28 - 10-10-2018
Try a different powder?
Optimal Barrel Length - VASCAR2 - 10-10-2018
For Gallantry Wrote:2245 FPS from a 120 grain TTSX over 27.0 grains of RL15 in Lapua brass...book velocities are over 2500 FPS
Hornady list max charge of 29.0 grains Reloader 15 with 120 to 123 grain bullets. Looks like you could get a little more velocity out of your barrel by going to a higher charge or different powder. Typical velocity with a 120 grain bullet in a 20” 6.5 Grendel is about 2475 to 2520 FPS from my testing.
Optimal Barrel Length - grayfox - 10-10-2018
VASCAR2 Wrote:Hornady list max charge of 29.0 grains Reloader 15 with 120 to 123 grain bullets. Looks like you could get a little more velocity out of your barrel by going to a higher charge or different powder. Typical velocity with a 120 grain bullet in a 20” 6.5 Grendel is about 2475 to 2520 FPS from my testing.
+1 ^^^ what he said.
Also with the longer barrel you could get some more ooomph with a slower powder... like maybe cfe123.
Seems like a 20-22-24" barrel would get you what you might be looking for.
One more thing, the 120 ttsx with a G1 of 0.412, doesn't have what I would call a 1000-yd BC... for bangin' steel why not go to a better-BC bullet. 129 Ablr, Hdy 123-anything, lapua scenar's, sierra SMK's.... lots of 1000-yd choices.
Optimal Barrel Length - muvef - 10-10-2018
RL15 is slow. Your numbers sound typical.