Nikon scope question

[PistolPete75]

Most magnified scopes need to be high enough to clear the rear sight (if you have one) and far enough forward so you can get good eye relief and a good cheek weld. On mine, that means the rear eyepiece needs to be a bit ahead of the charging handle.

The 2 main options:

- An extended riser that lets you mount the scope out over the handguard and medium-ish rings. The riser gives some height, and the rings give some more. Too much ring height along with a riser messes up the cheek weld, unless you have a cheekpiece.

This is the most flexible option, though there are more connections between your receiver and scope that can loosen up, add tolerances, etc. You also want to make sure there's room for your BUIS on the flattop rail behind the extended rail, as it won't zero if mounted on top of the extended rail.

YHM makes some good quality affordable risers in a variety of configurations. ARMS and others make them as well. ARMS also makes the #38EX or #38SEX extended rails with built-in ARMS #40 BUIS.

- A one-piece mount that extends the scope position out over the handguard. This is less flexible, but the most solid.

Armalite makes the least expensive effective one, IMO, but it's barely got enough forward relief for me. LaRue makes very popular ones, including an extended one, but I think they're for 30mm only (I may be wrong on this).

RRA makes a cheaper one, but it doesn't have as much forward eye relief as the Armalite or LaRue.

Here's a pic of my Armalite on my varminter:

i already have the arm#40 buis. i like the idea of the arms#38ex with medium rings. so if i get the Nikon Monarch Scope 3-9x 40mm BDC Reticle Matte
with the arms#38ex with medium rings, and i already have the arm#40 buis...i'll be good to go right?

[maxicon]

It totally depends on the scope dimensions. Welcome to the world of mix'n'match AR optics. It can be very frustrating to get a set of stuff working together, especially magnified optics and BUIS.

The ARMS 38 has the ARMS 40 sight built in, so you don't need both. The ARMS 36 is the same without the built-in sight, but I don't think you can mount an ARMS 40 behind it (I may be wrong, though - I don't have one). To use the ARMS 40 with a riser or extended rail, you'll need one that will allow the ARMS 40 to mount behind it (see below).

Medium rings would be fine in general, but are likely too low with the ARMS BUIS. Getting the scope above the ARMS might require high or extra-high rings, depending on the scope's dimensions.

Here are some examples. I need a lot of forward eye relief, and many mounts just aren't far enough forward for me.

I've recently mounted a 1337tactical Leupold LR/T clone 3.5-10x40 scope into a set of Warne medium height 30mm quick-release rings, and here's what it looks like with a few different rail configurations:

Mounted directly to the flattop - it fits, but eye relief point is way too far back for me, and there's no room for BUIS:


Mounted on an RRA scout rail - this gives me perfect eye relief with nose to the charging handle, but this rail has no provision for putting a BUIS behind it. This is how I'd shoot this one if I didn't care about BUIS, and is how I'll be testing this scope.


If I try to put the ARMS 40 on there, I run into trouble - the rings are nowhere near high enough. I need an extra 3/4" to clear the ARMS 40 (which is a pretty high BUIS).


(continued in next post)

[maxicon]

Here's the same setup with my Armalite one-piece and Mueller scope - closer, but still pretty far off. I'd need a half-inch riser that left room for the ARMS 40.


With the ARMS 38EX, it's the same issue, but I need less ring height, due to the built-in rail. The EX doesn't really give me enough eye relief - I'd have been better off with the 38SEX.


A nearly good solution on my CMMG M4 upper is the GGG scout rail, which leaves a slot free at the back, but it's not quite enough room for the ARMS 40. If I could move it forward one more notch, I'd be able to mount the ARMS 40, but then the rail hits the delta ring. I'd still need 1/2" more ring, but I'd be able to get both forward eye relief and have a BUIS that the scope clears. That's what I'd do if I needed a BUIS and this scope, and I'd have to take of a sixteenth or so from the rear of the rail so the BUIS would fit.


A good bet is to browse ar15.com for combinations that work well for other people. You may end up wanting a lower BUIS for more flexibility. Otherwise, you have to check out all the combinations that may work for your specific scope and BUIS. It's one reason you can buy lots of used optics/mount gear cheap at arfcom - people buy it, it doesn't work well for them, and they sell it off!

One of the real problems is that very few of the manufacturers of this stuff give any detailed dimensions of clearances, heights, extensions, and such. You just have to try it and see...