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AR Scope Question

I just put together a .224 Valkyrie AR. I took the scope off my Ruger 556 AR and for the life of me can't get the elevation high enough. We are talking over a foot low at 50 yards with the elevation knob maxed out. The Ruger was a high rise AR mount (due to the M16 style sights) while the .224 is low mount. I wouldn't think that would make enough difference but what you could adjust for it.

The Valkyrie is consistent in point of impact so I don't believe the gun is at fault. When the scope was on the Ruger, it was sighted to be dead on at 100 and did a fantastic job. I even took the scope off the 224, put it back on the 223 and it checked out. When I put it back on the 224, same thing.

The scope is a Nikon Prostaff 5 3.5-14 X 40 BDC and the ammo is 90 Grain Federal Matchking.

Any ideas on what is going on? I don't want to put the high rise mount on the Valkyrie. One daughter getting married in 2 weeks and the other in a month and wife probably wouldn't approve of a new scope quite yet. ;)

your scope's description: "Spring-Loaded Instant Zero-Reset Turrets

To simplify field adjustments, Nikon has integrated this feature into all new PROSTAFF 5 riflescopes. Just sight-in as usual, then lift the spring-loaded adjustment knob, rotate to your “zero”, and reengage. Field adjustments are now as simple as dialing-in your subsequent ranges."

is there a chance that, switching from rifle to rifle, this feature is hindering setting your zero? never heard of a scope that wasnt damaged ending up that far off at 50yd

.....sounds like you can lift and reset your adjustment knob to gain more adjustment if it's 'maxed out', just a thought

Possibly use shim stock to fix the problem.

Sounds like everyone has you on the right path...I use the Nikon M223 set-up on mine...

That's if I had one of those AR type things! ;-)

Bullet impact a foot below line of sight at 50 yards makes me wonder if the barrel is out of line relative to the line of sight of the scope.?

Here's my thinking:

When a scope is mounted on any rifle, the line of sight though the scope is a small distance above the axis of the barrel, usually 1.5 - 3 inches, depending on the height of the mounts, front lens diameter, etc. When fired, the flight path of the bullet is below this line of sight, but moving higher relative to the line of sight through the scope, resulting in the bullet's path and line of sight converging (usually at around 25 yards), after which, the bullet impacts above the line of sight for a distance until drop brings it back in line with the line of site through the scope (the sighted in distance). If for some reason the axis of the barrel and line of site of the scope are diverging, the rifle would hit low at every distance. The error would be small at close range, but get progressively worse at longer distances.

That explanation might be more confusing than I intended it to be. It would be easier to explain with a diagram.

Out of curiosity, have you shot it at 25 yards? The impact point will be below the line of site as it should be, but if the barrel is "out of line", the difference will be greater than the distance between the bore axis and scope axis at the muzzle.

Out of curiosity, have you shot it at 25 yards?

Sorry, trying to type on my iPad....

Update, even tho I have no time to play with...umm work with the rifle, I drove over to the hayfield and shot it at 100 yards (wife was at work so she couldn't fuss at me). it was shooting 16" low at 100 yards. JTV - I really didn't want to put high mounts on it, I liked the flat top down low. Push comes to shove, I can take the mounts off the Ruger and try that.

Shuteye - I forgot about the lift and turn on this scope. I hadn't had it off the other gun in 3 years or so. I'll have to hunt up the manual (or go online duh) and investigate it further. It being off that far at 50 really had me puzzled also.

Thanks for the suggestions. I have to leave the house Monday for 3 weeks of trainings and weddings in 3 states. I'll be home for 8 hours sometime during that time so there is no fooling with it until after all that. Unless I can get close enough to ready to sneak off tomorrow afternoon.

Let us know what you find out!

You should be able to get zeroed with any height level mounts. Sounds like a scope issue or a mount issue. A couple thousandths mistake in machining can cause issues. Scope height should be based on where it lines up correctly with your eye. Flattop, handle, whatever shouldn't change how high your scope needs to be above the barrel to allow proper form.

They make angled rails/mounts that allow more "up" adjustment. Make sure you don't have something like that on backwards.

I managed to work a little more with it after church while the bride was fixing lunch, Since she wanted to eat a little later it worked out well. ;) Looking it over, I decided the front mount might not be setting down as it should (I think it wasn't in the groove). Since they are quick disconnect mounts (UTG brand) I went ahead and switched sides with the disconnect in case they were angled slightly.

I also tried to reset the turret which seemed to allow a little more play but not much. I mounted it on the Ruger lower in case there was something messed up with the stock or the lower I put together.

Once I did all that I went forth and shot. I backed up to 10 yards and it shot high by a bunch, backed up to 35 (all I can get behind the house), still as high as it was low yesterday. Swap lowers, point of impact the same as with the other lower. I roughed sighted it in but to really get it fine tuned will have to wait a few weeks due to trainings and weddings.

Now, what actually was wrong? I don't know. Any one of those things or a combination of them could have been the problem.. I wasn't very scientific in my experimentation. ;) Anyway, thanks to everyone for your input, it was very helpful. I'm looking forward to playing with this gun and poking holes in things.

It was hard to tell but it seemed like that mount wasn't hooking on to the rail like it should. But it doesn't take much to throw things way off.

you need a 20 moa rail.

100% it was the mount.

I have a Primary Arms 3X prism reticle ACSS. I've been switching ARs mounting it on a 6.5 Grendel flat top and on occasion, to my .223 Wylde on top of the mounted carry handle by removing the mount that came with it and screwing it on top of the carry handle. The scope has reticle grids for auto ranging and tracking targets moving left or right at a distance up to 600 yards. You can shoot up to 1000 yards with just holding over but you have to read the wind. I use it on my .308 too using 175 grain HPBT Matchking. And I am not affiliated with Primary Arms. The scope cost less than $300.00 bucks. Good shooting and great hunting.

I had a similar problem with my .17 WSM. Turns out my front scope mount wasn't properly seated. After I fixed that I was driving tacks (ok quarters) at 100 yards.

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