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Posted: 6/30/2016 8:12:36 AM EDT
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Since I now have everything for my SPR build, it's time to put thought into an optic.
I haven't quite nailed down which scope I am going to use yet. And may not for a while. However, I have been reading what I can find on the subject of scope mounts. But most of what I am finding is one person's/company's view on a particular mount or two. I'm not looking for 100 replies with "The Grippy Grabber is the best, you should get it". Or "Just go get some cheap rings and you'll be fine". What I am looking for is information on what characteristics one should be looking for in a mount. I see prices ranging from $15.00 to well over $100.00. And I wonder what my dollars need to be buying. |
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IMO the most important factor is proper eye relief with your optic and preferred shooting position. Almost all optics on an AR will need some forward offset for proper eye relief. If you shoot Nose To Charging Handle (NTCH) like the military has often taught, you will need even more eye relief. Another important factor is sight height. The industry standard is 1.5" above the rail to centerline. I prefer slightly lower, but it can depend a bit on the optic and how low you like to be. Remember that the objective diameter can affect how low you can get and if you want a flip cap it will need a little more space. I would not go over 1.5" to centerline from the rail. The ability to return to zero is important for detachable mounts. My preference is Larue (I have quite a few), Midwest Industries (Haven't personally tried these yet), then ADM (Have a couple). I quit using Bobro. Midwest Industries locking system is very similar to ADM, but it has more adjustment positions than the ADM mounts. I feel ADM's adjustment system is a little course. I've had them be too loose to hold zero on one setting and too tight to open the clamp without a prying tool on the next setting. Most the time they work just fine though. I tighten Larue levers past the recommended 45 degree setting. I always perform a push test on my mounts, if I can move them back and forth, they aren't tight enough. Here is a video where I do a push test on a broken Bobro mount. https://youtu.be/V3TnMeqNjXo Some other items to consider are how much the mount weighs, how low profile/snag free are the mounting bolts/levers and what material is it made from. The really cheap Chinese mounts are likely to strip out the threads before they get tight. Mounts like Larue you can use 30in/lb without issues. I normally torque most of my scopes to 25in/lb, except Vortex scopes as they recommend 15in/lb as they occasionally have binding issues over 15 in/lb. On the budget side, I would look at Primary Arms extended mount, Aero Precision mounts and Vortex mounts. |
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Some very good information there. Thank you very much!
That really helps with the confusion and tells me I really need to concentrate on which scope I am going to go with, prior to looking at a mount. ----- I watched your video. Movement while locked down can't be a good thing. However, I found my scope. My birthday is in a couple weeks. Just box it up and send it 
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Quoted: Some very good information there. Thank you very much! That really helps with the confusion and tells me I really need to concentrate on which scope I am going to go with, prior to looking at a mount. ----- I watched your video. Movement while locked down can't be a good thing. However, I found my scope. My birthday is in a couple weeks. Just box it up and send it Your in luck! Amazon has an open box XRS for only $1854.92 (plus tax). I really like my XRS. I've got a Razor II 4.5-27 on order so I'll probably have a new favorite soon. I picked up my XRS on a clearance deal from Natchez for about $950. I wish I would have bought several more  |
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I guess you could do that, but I wouldn't. I would just look at the eye relief numbers and preferred shooting position. If you don't shoot with your nose touching the charging handle you will normally be good with a SPR length mount. http://www.larue.com/larue-tactical-spr-m4-scope-mount-qd-lt-104 If you do touch the charging handle with your nose then you will probably want an SPR-E style mount. http://www.larue.com/larue-tactical-spr-e-lt-139 If the scope has 4" of eye relief and your normal shooting position is within an inch of they charging handle, I would go ahead and get the SPR-E length mount. Personally I would take a SPR-S mount over the standard SPR mount as it sits .06" lower. It's really not much lower and they don't make it in the extended length though. http://www.larue.com/larue-tactical-spr-s-mount-lt-158 |
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Quoted:
Would it be a good idea to get a pair of cheap rings just to do a mock up with whatever scope I may get? Seems it would be the best way to get the scope where I need it. And then buy a mount based off that info. As pointed out above, the two ring solution usually does not work with most scopes on an AR15 because the top rail is too short and does not extend far enough forward to provide a place for the front ring once you get the scope to eye (eye relief) distance right. Your scope turret will be too far forward for the front ring to be able to attach to the rail. It will be suspended in the air. You could use an extended riser bolted to your receiver, giving you more rail slots out over the hand guard, and then use two piece rings, but there are a separate set of issues in doing that -- getting ring height correct, more mounting screws to possibly loosen and destroy your zero, machining tolerance issues that affect getting your rings aligned properly, and extra cost, being a few. A decent one piece cantilever mount resolves all of those issues for you. Several good choices are mentioned and illustrated above. I like and use both Larue SPR mounts and ADM Recon mounts, both QD. A less expensive alternative is the fixed one piece mount Leupold Mark 2 IMS for about $85. The least expensive solution that is reliable and I can recommend is the two piece cantilevered ring set from Nikon, its P Mount system. Those rings have a built in forward offset and are the right height. About $50 for the pair. Not something I care for, but they seem to work. Here is an example of what we are trying to tell you. This is my AR15 carbine. The 3-9 scope is typical in length and turret location. Note the position of the back of the eyepiece. Many (Jaqufrost and others) like it even more forward than mine. Note how far forward the scope turrets are, completely out in front of the first receiver rail slot. Putting a ring in front of them would suspend the ring out in the air off the front of the short AR15 receiver. The mount chosen is the Larue SPR LT-104. If you need your scope more forward you need the SPR-E or equivalent. I hope this helps make things more clear. 
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