Ran out of scope travel, Burris AR P.E.P..R mount

[usmc0352]

Ran out of elevation adjustment when trying to dope for 522 yards today. Had to hold over using the reticle. With my present zero at 95 yards, the most I can come up is 9.25 MOA. Scope runs out of travel. Shim up the rear of the mount? How much? The scope is a vortex Diamondback 30 mm tube 6x24. Should be plenty more travel I would think.

[Zeneffect]

6-24×50?

If so I have the same scope and run a 20 moa rail which should give me enough turret for 1000. Sounds like something is off if all you have is 9.25moa, almost like you also have a 20 moa rail, but it's on backwards.

[usmc0352]

I have the 410341 model and the rings are forward. It appears that the 34mm version is the only one with built in 20 MOA.

[VASCAR2]

You can get the specifications on the scope and should indicate the amount of possible elevation. Most of my scopes have 70 MOA of elevation adjustment. When zeroed at 100 yards I am roughly in the middle of the adjustment range around 35 MOA. On a 16” 6.5 Grendel with Leupold Mark AR 3-9 scope I ran out of adjustment around 800 yards. I went to a 20 MOA canted mount which will give you more adjustment range, instead of zero being around 35 MOA from bottom it is now about 15 MOA from being bottomed out. This scope has quarter inch click adjustment turrets so about 60 clicks from being bottomed out.

Checking spec for Diamondback Tactical 6-24x50 FFP scope shows 65 MOA total adjustment. The Burris Mount might not be setting level or out of spec. The scope could have a fault where the reticle is not moving or positioned correctly by the erector mechanism.

Using ballistic calculator shows 16.7 MOA needed to get to 600 yards. The scope should have roughly 32.5 MOA of upward adjustment. You could first try the scope in a different mount and see if that corrects the issue. If it doesn’t I think Vortex will fix or replace the scope.

[usmc0352]

Yes, 6x24x50. I will confirm that the mount is sitting flat on the rail for sure.

[Mesa1978]

I have that scope, in Mils, it should have enough elevation without needing a 20 MOA mount.

[usmc0352]

That's what I thought too. Seems odd.

[usmc0352]

A .020" shim under the rear of the base gave me 32MOA more elevation capability.

[VASCAR2]

Sounds like the mount/base is the culprit because the scope still could move once shimmed. Thanks for the update.

[Stephen Vick]

I ran into the same problem when trying to zero in my AR in 6.5. I have an older Black Diamond in an 8x32x54 It also ran out of travel. I thought scope was broke so I sent it back to Burris for a diagnostic and it checked out fine. I bought a Warne 20 MOA mount, and it appears to have remedied the problem. Apparently, Burris scopes don't have the same amount of travel as Leupolds which is the only other brand I have. I got the Burris for a really good deal off a friend who learned the hard way about those Super short magnum caliber and barrel life. Vascar2 you seem very knowledgeable. I dont have a crono and have been shooting Hornaday Black 123 grain I think. What kind of barrel velocities do you think I would get if I put on a 24 inch barrel as opposed to the 20 I am running? Would it make that much difference? I have a 24 on a 5.56 I love.

[Zeneffect]

Not much.

Here is hornady black 123gr from a 22"

[VASCAR2]

This might help but the trend is pretty clear. These results were from a few years ago on a 70 degree day using a Magnettospeed chronograph, five shot strings.

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

I can post the specific results but they have been posted before. In general going from 20”-24” you gain approximately 60-100 FPS higher velocity with the 24” barrel.

[Stephen Vick]

Thanks guys. Looks like it probably wouldn't be beneficial enough to spend on a new barrel with only that much of a velocity increase.