Thursday, October 23, 2014

Just the Basics – Mounting a Scope to an AR-10 and Zeroing


Let’s spend a few lines talking about the whys, wherefores and “how comes” of even having a scope on your AR, the type of scope to choose, how it matches the ammunition you shoot and how this plays into mounting, zeroing and using a scoped AR.

I have two ARs as part of my defensive weapons – A Panther Arms “Oracle” .223/5.56 and a Panther Arms AP4 .308/7.62 NATO. I call both of these weapons “utility” weapons. I have found them durable, accurate and reliable with a very reasonable price point. There are cheaper choices . . . and oh so much higher priced options. That said, these are what I have chosen to defend my family with and I am happy with their performance.

I have not scoped my AR-15 – the “Oracle” - because I see it as a weapon that will typically be used within 100 yards. I do have an Eotech 517 mounted on it and co-witnessed with set of iron backup sights. Should the need arise, I can shoot a 3-6 inch group at 100 yards with either sighting method. However, I believe most of the work will be done within 50 yards and either sighting system provides more than enough accuracy for my needs. This is the sighting combination that will stay on the AR-15.

For distances past 100 yards, a sighting system that provides more assistance to eyes that don’t see quite as well as they did 40-50 years ago is a real help. Add to that a weapon that can consistently reach out and touch something or someone at greater distances has real value. Something that could be used for hunting larger game as well as slowing 2-legged threats may well prove useful should the wheels ever come well and truly off the cart. My choice has been the Panther Arms AP4 in .308/7.62 NATO.

I then began to look for a rifle scope that could easily be used for both hunting and personal defense, that was from a reliable manufacture and that didn’t cost as much as the rifle itself. I settled on the Nikon 3x9 Prostaff with a BDC reticle. The scope is designed for both standard velocity cartridges – 2800fps and high velocity cartridges – 3000fps. Again, while there are certainly scopes with much higher price points – at under $200, this scope does an excellent job.

The mounting rings I chose were the TMS Heavy Duty Tactical mounting rings to mount the scope to the Picatinny rail milled into the upper receiver of the AR-10.

To place the mounting rings on the scope I utilized a level surface – checked with a small level – to insure it was perfectly flat. Then I put the scope within the rings, attached the top half of the rings and loosely tightened the screws. I set a small level on the windage adjustment and rotated the scope until it showed level. Then I tightened the rings going cross-corner, front to back a little at a time. Final level adjustments were made and final torque adjustments were made to the individual ring screws and the scope was wedded to the rings.

I realize this is not “traditional” but with a milled Picatinny rail on the upper receiver, as long as the scope is parallel within the rings – it will be on the rifle. And, it’s a lot easier to handle the scope alone without having to do the same process after first leveling the AR-10 in a jig. The final results – on the range – assured me this method worked fine.

Level Scope (Medium)

Next I mounted the scope to the weapon, adjusted it front to back for a nice image when I made my cheek weld, and headed to the range.

AR 10 With Scope (Medium)

The ammunition I was shooting was Winchester 308, 150 gr Power Point, X3085. It’s a nice general purpose hunting round suggested for everything from deer through elk. It has a muzzle velocity of 2820fps, well with in the capability of the scope. Honestly, I have these because Cabela’s had a deal on 1,000 rounds of them a few years back. Still, good enough for any work I would expect to do.

I used a standard 100 yard target and started on the 25 yard range. Please . . . don’t be “that guy”. We’ve all seen him – sitting at the 100 yard bench with a brand new rifle, scope and iron sights “sightin’ in his gun”. And cursing a blue streak because he can’t find the paper, let alone hitting a standard 100 yard target. The purpose of starting at 25 yards is to get your rounds on paper to begin with, get a 25 yard zero, and then move to 100 yards. If you do that, you’ll be on paper with your first rounds.

Next, please – don’t just blast away, adjust, blast away, adjust . . . as in most things – there is a “method”. Personally, I use a “3-round” method. I shoot 3 rounds, adjust and repeat as necessary. You should easily be able to set your zero within 3 to 4 3-round groups.

Nikon Zero 25Y (Medium)

As you can see from my 25 yard target, out of the box my scope was significantly “low”. At 25 yards your “one click per ¼” at 100 yards” becomes more like 16-ish clicks per inch. So you can easily see should I have started at the 100 yard range, my rounds would have been low and well off the paper.

The above photo will show you the results of the process. Basically, I look for a 1”-ish group in/near the center of the target before I move to the next distance. As you can see it took 12 rounds. I can typically manage zero in 9 rounds, but I forgot the distance when I clicked off my first adjustment. Details, details, details . . .

Nikon Zero 100Y (Medium)

Next I moved to the 100 yard range. As you may have already anticipated, my first rounds were high - on paper, but a couple inches high. This is because if you zero at 25 yards, you will hit high at 100 yards. Conversely, zero at 100 yards, you will typically be a couple inches high at 25 yards . . . something to remember for your defensive carbine if you zeroed at 100 yards and attempt to make a head shot at 25 to 50 yards.

This process went quicker with my zero coming in after 9 rounds. It was a bit rushed as I was trying to make a meeting and “needed” to leave. The result can be seen in the group sizes. Still, group 3 is 1.5”-ish and I am OK with that. Total rounds expended - 21. It doesn’t need to take all day – or even more than 9, there are tools you can buy to speed things up. I could have bore-sighted it first with a laser round for example. But, I like a more traditional method so I’ll give up the additional rounds just for the range time.

The scope will also remain “wedded” to the AR-10. I’m not much for swapping hardware between firearms. Obviously I may need to re-zero with a change in ammunition, but it will be awhile before I finish off my stock, so I’ll be good for some time.

It is always good, before you head to the field, to insure your screws and mounting nuts are tight. A couple hundred rounds down range shouldn’t loosen things . . . but a quick check never hurts.

Zeroing a scope. It’s not rocket science . . . oh wait, ballistics actually is a rocket science . . . Take your time, have a plan, get a good scope and good mounting rings – and don’t be “that guy”.


  1. And never try to adjust windage AND elevation at the same time... you'll chase that sucker all OVER the paper... sigh

  2. Your post is very helpful, thank you. Hunting has evolved throughout the years; from being mankind’s main source of sustenance to being a recreational sport with guidelines and limitations. The tools that come with the sport have evolved as well; from primitive axes and hunting snares to precision bow and arrows and rifles that can hit a target a few hundred yards away. See more

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