Adjustment Range and 20MOA mount

[AFCATM]

I am about to finish my Grendel build and I'm searching for a scope to shoot up to 1K yards. I've narrowed it down to a Nikon FX1000 6-24, which has 17 MRADs of internal elevation adjustment. To calculate my max range with the scope (dialing in), would I just multiply the 17 mils X 36 inches (mil @ 1K) to get the maximum adjustment of 612 inches and make sure that whatever bullet I am shooting does not have a bullet drop more than that @ 1K yards? Also, I am assuming that I will lose some adjustment during the zero process and that 612 will decrease.

What is the typical MRAD adjustment you needed to get your scope zeroed, and thus not available to you when shooting long distance?

Has anyone run out of elevation adjustability when shooting a Grendel round out to 1K on a flat mount?

Do I need a 20MOA mount?

[Bigs28]

What elevation are you at? I would get a 20moa mount anyway but that's me.

[Klem]

AFCATM,

I would approach it differently. First, figure out what elevation you need to reach the intended range. This varies depending on how high above sea level you are. The Grendel is a relatively small case so if you want velocity you have to rely on barrel length. How long is your barrel? I ask this because you can then work out the maximum effective range and then how much elevation you need to get there.

If your 123gn bullet is about 2450fps you are going to need about 13Mil to get to 1K yards.

17-MRad does not sound like a lot of elevation so I went looking on Nikon site for specs. Elevation is not listed on their online spec sheet. If they have properly centred the reticle in the factory it is you have exactly half of that up, and half down. So without the assistance of a canted mount you have 8.5MRad of elevation (equivalent to 29MOA). For long range shooting you definitely need a canted mount. A typical 20MOA will give you another 6Mil. This gives 14.5Mils total. This means you won't run out of turret elevation at 1K. But if you do you can use the reticle graduations which on that scope are in Mils. At 1,000 the bullet will be approaching Mach-1 so it will be the bullet, not the scope that will limit your usable range.

[Randy99CL]

I always buy a +MOA mount because it often doesn't cost any more.

With level base and rings, half your elevation adjustment is usually wasted.
My newest scope has 80moa of total adjustment, so normally that would be +40 and -40 that I can never use. A +20moa base moves the centerline so that I have +60 and -20; a much more usable range.

[NugginFutz]

I am about to finish my Grendel build and I'm searching for a scope to shoot up to 1K yards. I've narrowed it down to a Nikon FX1000 6-24, which has 17 MRADs of internal elevation adjustment. To calculate my max range with the scope (dialing in), would I just multiply the 17 mils X 36 inches (mil @ 1K) to get the maximum adjustment of 612 inches and make sure that whatever bullet I am shooting does not have a bullet drop more than that @ 1K yards? Also, I am assuming that I will lose some adjustment during the zero process and that 612 will decrease.

What is the typical MRAD adjustment you needed to get your scope zeroed, and thus not available to you when shooting long distance?

Has anyone run out of elevation adjustability when shooting a Grendel round out to 1K on a flat mount?

Do I need a 20MOA mount?

First, welcome to the horde, AFCATM. Your uniqueness adds to the collective.

It is important to take note that 17 mil of elevation is for both upward and downward correction, so what you will actually have available for upward elevation will be ~ 1/2 of that, or 8.5 Mil.

Consider that, if your scope and barrel are perfectly aligned, their optical and physical centers will run parallel from the rifle to the target, no matter the distance. The two will be separated by 2.5 - 2.75", depending on the mount.

Now, assuming the typical 123 grain pill, flying from a 18" barrel @ 2450 fps, you will get about 3" of drop @ 100 yards. That's .8 mil correction to get it up to the bore. Now add to that another .6 mil for the 2.5" scope height, for a total of (approx) 1.4 mil just to get zeroed at 100 yards with average ammo.

This means that your scope will have about 7 mRads of elevation left over, plus or minus.

You don't mention your MV, altitude or BC so, again, I estimate the following:

Let's assume a barometer of 29.9 "Hg (sea level), the same 2450 fps and a G7 BC of .255. (123 ELD)

Total drop at 1000 yards is just about 13.5 mRad, leaving you short a bunch.

Now, shoot the same bullet at 5000 ' (24.75 "Hg) and your drop is 10.4 mRad. Still short, but within the average 3 mil or holdover available within most reticules.

So, the long answer is you will want that 20moa mount, if all you have is 7 Mil available in the scope.

[NugginFutz]

My newest scope has 80moa of total adjustment, so normally that would be +40 and -40 that I can never use.

Randy - your solution is simple. Turn the rifle over, and work it from there.
You're welcome.

[AFCATM]

You guys make very good points. I had incorrectly assumed that the adjustable range was actually all usable. It does make more sense that if the reticle is exactly in the middle, then the adjustable range is split in half and that cuts my usable range significantly. I will be using a 20 inch barrel and shooting at maybe 200 feet above sea level. Yep 17 MRAD is mentioned in the text under one of the pics on the Nikon site.

Does the 20MOA mount reduce the clearance between the front of the scope and the handguard? It has a 50mm objective so I’m wondering if I will have issues up front. I have a JP handguard but will not be putting a rail on top so I think that will buy me some space.

[NugginFutz]

Does the 20MOA mount reduce the clearance between the front of the scope and the handguard? It has a 50mm objective so I’m wondering if I will have issues up front. I have a JP handguard but will not be putting a rail on top so I think that will buy me some space.

Most of the 20moa bases account for this. My 50mm has PLENTY of clearance above the hand guard. Just take note that the occular end will be a tad bit higher than normal, which may create cheek weld issues for you.

[Klem]

AR's have typically 2.5" between the bore and scope axis. That's heaps of clearance for a forward cant mount.

Close to sea level with a 20" barrel you will just be able to make it to 1,000 without needing to use the scope reticle, as long as you have a 20MOA mount.

[biodsl]

Does the 20MOA mount reduce the clearance between the front of the scope and the handguard? It has a 50mm objective so I’m wondering if I will have issues up front. I have a JP handguard but will not be putting a rail on top so I think that will buy me some space.

I'm running a 44mm objective in a 1.125" high mount. I have .3 inches between the objective and the handguard. Most mounts are 1.375 and 1.5" tall. You should have room. Many on this forum run scopes with 50mm objectives.

[Randy99CL]

Does the 20MOA mount reduce the clearance between the front of the scope and the handguard? It has a 50mm objective so I’m wondering if I will have issues up front. I have a JP handguard but will not be putting a rail on top so I think that will buy me some space.

Doing the math, it looks like 20moa tilt works out to be .0056" per inch so if your scope is 14" long the objective bell would be about .040" lower than a level mount. That's not much at all and most don't need to consider it.

[mdewitt71]

As mentioned above.... just get the 20MOA mount, you will be glad you did if or when you need the extra elevation.
I run 20MOA mounts on my 20" Wylde and my 18" Grendel.


BTW the FX1000 is an amazing scope with some very nice glass..... it will serve you well for sure.
The Nikon Black 20 moa mount is a perfect match.

https://www.sportoptics.com/nikon-black-fx1000-6-24x50-16515.aspx

13% coupon and free mount.

[bman940]

md, that is a heck of a deal! I have been telling folks about the Promo Nikon is running until the 26th of Aug. Nikon's BLACK FX1000 is a great prie already for an optic that is loaded with useful features for longrange shooting. Getting the free mount a big bonus. Nikon's BLACK Series mount is very well put together, rock stable lock up and built tough. I don't know anything about the 13% coupon but that is also a heck of a deal! If you were on the fence about this scope, all of this should push you over to buy 1! make sure you do a range report after you get one too.
Here's a pic of my BLACK X1000 scope with the BLACK Series mount on my 6.5CM Bergara