Grendel and 5R Rifling (Haters gonna Hate)

[woohoo]

This conversation has been spread out over a couple threads so i decided to consolidate the conversation. To sum up 5R rifling is providing higher velocities with the grendel. 5R rifling doen't have the 90 degree angles which means higher velocities and less copper fouling.





Hornady 123 Amax measured from my and a friends 24in AR-Stoner barrels has a MV of 2650fps vs 2580fps quoted by Hornady. Out of my 18in AR Stoner i'm getting 2560fps. Thats about what you would expect from a typical Grendel with a 22in barrel.

[video=youtube;49GsxciNPUc]http://www.youtube.com/watch?v=49GsxciNPUc&feature=youtu.be[/video]

One of the main criticisms of the Grendel usually levied by the 6.8SPC crowd is lower MV but as you see the 5R rifling gives the Grendel at least a 80fps boost. Now you can both get good muzzle velocities and long legs and good accuracy. The faster the load the more performance boost you'll notice. When your shooting the lower grain pills like the 100gr and 95gr fast you can see as much a 150fps boost. I've cronyed 3 AR Stoner rifles now with factory Amax and all three are shooting much faster than other Grendels with the same ammo. 6.5mm pills are longer and have larger surface area that contacts the rifling. Therefore 5R rifling is going to benefit the Grendel more so than shorter fatter calibers like the 6.8SPC.

AR Stoner barrels are the Midwayusa brand and are made by liberty barrels and come with 5R button rifling.

What load are you using to push a 123 to 2650fps out of a 16" barrel?
The photo of the button you posted is really a Hybrid 5R like we use. An Obermyer or Rock has a different land shape, angled but different than shown.
On the same page you took that photo from but further down the page-
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I have not bore scoped a Satern to see if it is like the Obermyer or if it is a Hybrid. There were posts on the old Grendel forum as far back as 2007 showing the velocities possible with 5R barrels but it is more than just the shape. Bore area, groove diameter and land to groove ratio all play a part in accuracy, pressure produced and velocity. Tweaking all of those can get you a barrel that is much faster but not so accurate or super accurate and a little higher pressure, just depends on what is more important to the person designing the button.
Maybe Bill A. can chime in but it looked to me like the less expensive AA barrels may be a 6R. I didn't spend a lot of time with it or video it but through the borescope the lands looked like they had sloped sides.
These are MAX loads in my 264 5R barrel with a .100 freebore. Some of the max loads shoot 1 MOA easy enough if that is good enough to hunt with. To find 1/2 MOA most need to be dropped 1/2 -1 gr.

123AM 2.3 748.. 31.5 2643 CCI450 20" max charge
123AM 2.3 335.. 29.5 2672 CCI450 20" max charge
123AM 2.3 4895 29.5 2650 CCI450 20" max charge
123AM 2.3 530.. 28 2682 CCI450 20" max charge
123AM 2520 31 2660 BR ........20" max charge