View Full Version : Problem with mounting Scope on AR***post 5

04-18-2012, 11:46 PM
I have a Nikon Prostaff 3-9x40 Matte BDC scope that i've been using on my 10/22 that i'm going to mount on my M&P 15 sport. What kind of rings should I get? I mounted it with the rings i have for my 10/22 (I believe they are 1") but the front A2 post is in the way and i have to take my rear magpul site off which isn't a huge deal for me.

I just need some advice on what rings to get so I can mount the scope.

Thank you guys!

Please go to Post 5

04-19-2012, 3:30 AM
1" is the tube diameter of the scope not the ring height. Go to Midwayusa.com home page, scroll to the bottom and look through the available reference material and guides. There should be a scope ring guide that will let you see the different heights from low to extra high. If you know what you have, you can reference off the guide to get something taller. Might need to add a riser to clear the front sight even with higher rings

04-19-2012, 5:03 AM
go for a one-piece cantilever mount -- i think they're a better solution for AR rifles. they look like this:


the one in the image (from larue tactical) is one of the more expensive models out there, but there are plenty of other quality options available for much less.

it might look odd, but there's a reason: you don't want to attach rings to your handguard, because you'll lose zero if the handguard gets loose and twists at all (unless you've got some hot piece of gear you're not telling us about). but if you don't, it's hard to mount your scope far enough forward to get the proper eye relief most scopes require. a cantilever mount sits only on your upper, but pushes the scope forward, like this:


you don't really need to get higher than the front sight post -- once you zoom in a bit, you'll focus right past it. most cantilever mounts should place the center of the scope close to where your sight line would be with irons, so you can keep a consistent cheek weld between the two different sighting methods.

if you want to keep your rear sight, get a mount with a quick-detach system (the mount in the photos has one) that lets you quickly remove the scope and switch to your iron sights; many manufacturers claim their QD systems will let you reattach the scope with no appreciable loss of zero.

04-19-2012, 9:28 AM
^^^ This, I was thinking about that after I posted where to find the rings guide. A one piece will get you up and out. If you don't want to spend a lot of money, check out Primaryarms.com, they have several from about 30 bucks shipped and up.

04-19-2012, 12:56 PM
So I went to Tripple A Sporting goods in Vallejo and talked to them about what mounts they had. Right now I can't afford $80 and up mounts so I went with what they recommended, some Leupold rings.

My problem is that it is a very tight fit. The front of the scope touches the hand guard.


And I have to be above 6x on my 3-9 scope in order to not see the front A2 post at all. 3-5x the front post takes up almost the whole picture


I guess my question is what do i do. This is my first AR so i'm very new to this all.... :face palm: If i'm forced to buy a more expensive mount i'll have to see whats on amazon because I do have a $100 gift card on there from selling some school books.

Do i get a riser? How much will that effect my cheek weld and how the optic work with distances being higher off the bore? Any Help would be greatly appreciated.

04-19-2012, 1:03 PM
Get one of these:


Also make sure you level that scope before you tighten it down.

If I had a nickel for all the canted scope I've seen....

Also, define "Distances" I wouldn't get to worried about the scope height vs POI at further range on a .223

04-19-2012, 1:09 PM
High and forward. The ocular lens should be back even with the charging handle or even a little more forward.

04-19-2012, 1:23 PM
Get a taller ring should solve your problem...

04-19-2012, 1:27 PM
Here you go: http://www.amazon.com/Burris-410344-AR-PEPR-Scope-Mount/dp/B004S76WTE

04-19-2012, 1:30 PM
At Amazon.com, I would recommend looking into either the Burris PEPR, or Nikon M223 mounts. Both are 1 piece cantilever mounting solutions designed for the AR platform which should fit your budget.

There is a version of the PEPR which has QD levers as well.

04-19-2012, 1:55 PM
don't worry about the front sight post appearing ... as long as it's blurred out enough that it doesn't obscure the target, just concentrate on the target. if it really bothers you that much, switching to a low-profile gas block is honestly a better solution than trying to get the scope to an impractical height.

that being said, the rings you bought are too low, which is why your scope is scraping the handguard. a cantilever will put your scope at the proper height. your ocular lens (the eyepiece) is also WAY too far back with this mounting.

sell the rings and buy the right tool for the job. this fantastic page (http://www.maxicon.com/guns/optics/one_piece/ar15_onepiece_mounts.htm) calls the PEPR the "best bet in the under $100 mount market." if you're bound and determined to use rings, there's also some information specifically for you near the bottom of the page.

just don't get the NCstar or leapers/UTG models, which are value priced for a reason -- you'll get what you pay for. and don't get a model with just one ring -- those are made for red dot sights.

04-19-2012, 1:58 PM
I would get a Larue Mount. They also sell rings, and if you call them, they will tell you the ones you need.

In regards to the front post, if you would like to shoot in low magnification, get a flipup front sight.

GG&G sells a good one, or you can go with A.R.M.s

04-19-2012, 2:01 PM
Thanks guys.
Looking at the Nikon M223 mount. But will it raise up the scope enough so there is some clearance from the hand guard and charging lever?


04-19-2012, 2:48 PM
The M223 mount works with their 3-12x42 M223 scope, so clearance should not be an issue with your 3-9x40 scope.

04-19-2012, 3:09 PM
Like many says, you need it higher.

Besides, the buffertube changed the usual rifle stock which means your eye will sit a little higher then a rifle stock, that means to compensate for that height, you get a higher scope ring so you eye level will match. You dont want to be crounched down forcing yourself to see the crosshair.