Scope ring height. How do you know?

P

Pond James Pond

New member
I'm looking into a new scope. A new scope invariably means new rings, soI'm having to add those to the costs. The problem is I don't know which height I'd need.

The platform is an M400 AR, the scope likely a 1-4x20/24.

I need the scope to clear the rail, but I don't want it level with my hair line as I'd like to keep the stock standard, and not have to buy additional cheek padding to raise my check-weld point.

So what is the rule of thumb?

Is it some kind of height above the bore?
Objective diameter?
 
You can pre-measure easily. Just don't trust the makers "HIGH, MED, LOW" definition they all vary.

Take these measurements.
1: Diameter of front bell.
2: Diameter of rear bell.
3: Diameter of tube
Divide all of them by 2 (this gives you a center line.)
4: protrusion of turret body below tube
5: Measure the barrel diameter at the mount rail
6: divide by 2 for the center line
measure from the barrel bottom to the rail center.
subtract the figure from (6)
7: Your ring, measured from the bottom center of the mount base to the center of the ring height (frequently where the ring splits).

The measurement from (7) should be greater than 1/2 tube diameter, the bell radius's from (1 & 2 should be less than the height from the rifle body to the scope at the point where it will rest.get the ring with the minimum over you can find.
Check that (1/2 (3) +(4)) is going to clear.

This will be the lowest mount possible, add a couple of mm just to be sure & buy whatever fits best.
 
Whatever height the scope axis is above bore axis, you'll need the stock comb to be at the right height to rest your head on without straining any muscles to look through it. If the stock you have ain't right, modify or replace it.

This is just one of those compromises we deal with setting up a rifle's sights.
 
Whatever height the scope axis is above bore axis, you'll need the stock comb to be at the right height to rest your head on without straining any muscles to look through it.
Click to expand...

That is why I am looking mainly at red-dots or the low profile 1-4x scopes.

Not only do they meet my needs, they also need the fewest alterations.

At the moment I am making do with a relatively cheap red-dot which you can see here in a post from another thread. Please note, I have since put the MBUS on the right way round and moved the dot site back another inch.

At present I can get a good cheek weld and stare right through the centre of that red dot. With the scopes I am considering, I think it is at least feasible that I can mount the scope at a similar height above the bore.
 
So, you want the center of the scope to be the same height as the center of your red dot. How high off the rail is the center of your red dot?
 
So, you want the center of the scope to be the same height as the center of your red dot. How high off the rail is the center of your red dot?
Click to expand...

OK, I was probably a little inaccurate there: My cheek weld puts me perfectly in line with the peep-hole sight which comes with no surprise. Due to the nature of Red Dot Sights the reticle is on target if looking through the sight dead centre, or off closer to the edge. In the case of my RDS that means looking through it about a third of the way up from the lower edge.

So, using my peep-hole sight, my line of sight down the length of the barrel is about 3.5cm (1.377") above the rail.

However, I am having a few issues using that fine Brownells chart (thank you topnpr).

Based on the Nikon 1-4x20 Monarch 3 I am considering can see that the objective OD is significantly smaller (25.4mm) than the eyepiece OD (41mm), so do I use the wider eyepiece OD, or the recommended objective OD?

My logic banks tell me it should be the wider, regardless which, making it the eyepiece. As such the chart tells me I need a .307" gap from rails to tube.

Meanwhile if we take the peep-hole measurements, and a 1"/25.4mm tube I would need the scope to sit 22mm/0.87" above the rail to put the tube centre at 35mm/1.377" above the rail.
 
On the scope you are thinking about:

eyepiece dia/2 + folded RR sight height = ring/mount height(rail to tube) + tube dia/2

Solve for ring height. Choose the next highest ring or mount.



On a 3-9 or large objective:

Do the calculation above.

Also,
objective dia/2 = ring/mount height(rail to tube) + tube dia/2

Stock adjustment:
ring/mount height(rail to tube) + tube dia/2 = 1.5 + A

A is the amount your stock should be adjusted. Typically, I would say under .5" do nothing, over, look for a stock.
 
DNZ specs say the Freedom Reaper mount puts the center of the scope 1.375" above the rail.
Burris PEPR or the highest Burris XTR rings put it at 1.5."
There are lots of AR mounts and rings in this height range. They give you plenty of room for a 50mm objective scope.
 
That chart doesn't seem to include the shooters' relationship to the stock and receiver, just the scope dimensions.
Click to expand...

Well, sure doesn't. There's obviously no way to account for those variables.
The taper of the rifle's barrel, the fore/aft placement of the scope, and of course the shooter are all applicable.

To the OP, it's critically important for a consistent sight picture at long range that your shooting position on the stock comb be the same, every time.

Take the rifle, close your eyes, and position your head/cheek on the comb comfortably and naturally- I've heard a military sniper comment that you should be able to fall asleep (perhaps a bit exaggerated, but you get the idea)- and then open your eyes and be looking straight down the scope.

After positioning yourself, you move the scope to fit your sight picture when you open your eyes- not the other way around. If your sight picture is too low, you raise the comb via a stock pack or adjustable cheekrest. If too high, taller rings. It helps to have someone else slide the scope back/forth in the rings while you maintain your shooting posture to get the correct eye relief.

I don't do it personally, but I've also seen it suggested to place a dab of silicone on the stock right at the juncture where your cheek meets it, so that your sight picture down the scope is exactly the same, every time. Again, it's all about a natural and comfortable position behind the rifle, and a consistent sight picture.

Sometimes I'm sure, there is a combination of a scope, and a stock with a high comb that the shooter just can't get low enough comfortably to shoot- and if that occurs there would be no choice but to cut down the comb or replace the stock.

There are too many variables to be sure of getting the correct ring height first time. If you're lucky, the optic will be as low to the bore as possible- and your sight picture low. Then, it's just a matter of raising your sight picture as needed with a stock pack.
 
New situation.

OK. Here's the situation.

I had overlooked one aspect to my set-up: my front sight post. It sits 3.5cm high in relation to the picatinny rail on the receiver.

I am on the verge of ordering a Nikon Monarch 3 1-4x20 scope.

I have since realised that, being a fixed front sight, it would be occupying the bottom third of my sight picture at 1x mag. That makes using the BDC, for example, much harder.

Would a Leupold High Q-R ring kit raise the scope high enough that the front post would not get in the way?
Note that the front sight is 3.5cm above the rail and the high rings only stretch to 2.5cm (1").
 
My first 2 choices would be

1: a see through riser so you can use both sights without them interfering with each other.

2: see through rings to achieve the same result.

Both would give a high scope mounting but you're stuck there anyway if you keep the front sight you might as well at least have it usable.
 
I've yet to see those on sale here, so I don't want to count on that as the sole solution.

That is another reason for Q-R rings: I'd be able to take my scope off, should I choose to go for the irons.

So, would 2.5cm rings make the front sight less intrusive? (at least sufficiently so that I can ignore it.)

In another thread about cheek rests, marine6680 feels they wouldn't get in the way which is promising.
 
similar situation

I put a more powerful scope on my ar today. The rep at the store said I had 90 days to decide if I wanted to keep the original scope, or get something else. I also bought a set of high rings as the rep said they would be high enough for the front sight to not get in the way, and I would then have a much stronger mount for my scope. I take the scope off to shoot off hand with the irons at an indoor pistol range, and when it is at home. I use the scope for 100 yards outside. When I was installing/leveling the new scope, I could now see a green haze in the optic at lower power. My front iron sight post is painted green. I had never noticed the haze before. I put the old mount back on. Same green haze at low power with the new scope. The old mount is about 1/4" higher than the rings that I attempted to use. The scopes were Nikon p223 3x9 (original), and p223 4x12 (new). Is this normal? The haze is not noticeable at full power.
 
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