Something I see come up in the forums quite frequently is the discussion of scope leveling. There’s the issue of the scope being level, the rifle being level, and all of them being in sync with Earth’s gravity. In this experiment I wanted to find out how much, if at all, it matters if the rifle is level-aligned with the scope. How? By mounting a scope very, very tilted, then shooting it 500 yards.

There are a few different parts of a scope that need to all be in sync with each other or it’ll likely cause you issue on the firing line. They are:

1.      Reticle

2.      Turrets

3.      Saddle

All of these elements need to be running parallel and/or perpendicular to each other. During the manufacturing process the main tube has a bottom flat machined onto it in the center. That flat is the saddle. That’s the source of truth for machining the rest of the main tube’s other parts like the turret bores and the erector tube’s witnessing location. Inside the erector tube of course is the reticle. This all results in the reticle’s vertical crosshair being parallel to the elevation turret’s direction of travel. It also makes it so the horizontal stadia on the reticle is running parallel to the windage turret’s bore and travel.  

If there’s error in any of those three parts in relation to being parallel and/or perpendicular you won’t have true dialing in relation to your reticle. The result would be, for instance, dialing 6 MRAD of windage and getting only 5.8 MRAD of elevation with something like .2 MRAD of windage. Good luck countering for that. Your scope needs to be true in all these aspects. 

A plumb line is a line going straight down to Earth’s gravity. It’s important to have the scope level with gravity when firing. It’s becoming quite common to have a scope-mounted level for the user to be able to quickly and accurately determine if their scope is level. When mounting that level it’s important to have it aligned with the scope’s reticle/saddle/turrets. This brings up a question. Does it matter if all of the aforementioned are aligned with the rifle’s vertical centerline for hunting, medium & long-range practical purposes? 

Scope height over the bore line seems to have some controversy at times. Some believe that the scope needs to be mounted as close as possible to the bore line, otherwise, as low as possible. Some say this is a myth.

From what I’ve personally experienced, the greater the shooting distance the less it matters, and it doesn’t take much distance for it to matter very little. It seems like most rifle setups are going to be 2 inches or less. When you’re shooting a rifle sighted in for 100 yards with a 2” sight height and you go to engage a target at a short distance like 5 yards you’ll certainly notice that height as the shot lands below the aiming point. There’s a reason ballistic applications have sight height input, but the apps take care of that consideration for you and it's a constant that can and is accounted for.

What’s all this have to do with today’s experiment? Well, what if that distance weren’t directly above/below in relation to the bore and sight? Say, diagonal. Diagonal because the scope isn’t mounted level with the rifle. What then?  

To try out this experiment I decided to use something that would require me to dial the scope a decent amount to make sure it was putting the mechanics of the scope being tilted to the test. Given I was only going 500 yards, I used a Howa 1500 Mini Action chambered in .223 Remington in a Boyd’s stock. The scope’s an Elite Tactical XRSII 4.5-30x50 scope in some Weaver 34mm rings and on a 20 MOA base. The scope was mounted tilted about as far as I could before the saddle was going to touch the scope base – roughly in that 30-degree realm. 

To deal with the awkwardness of the tipped over setup the front was on a Champion Target pivoting bipod and the back was supported in an Armageddon Gear Game Changer.

For ammunition I went with American eagle 55-grain with an advertised speed of 3240 feet-per-second. My hope with this ammo was that the 55-grain bullet would make it drop more to get to get to the 500 yard target to further stretch the dialing.

First off, this was a different sort of shooting challenge. The real challenges here were trying to not let the nearly falling over rifle have a negative effect on the shooting itself. While the bipod was doing most the work, it still required my putting torque into the grip that I normally wouldn’t have. This made trigger pulling harder than usual so I was struggling to put together great groups. Admittedly, I also don’t use a scope-mounted level usually. I can usually manage to keep my scopes level while shooting pretty well without one.

The ammunition I was using isn’t exactly match ammo, but it shot surprisingly well out of this little Howa. I didn’t bother chronoing the ammo out of this rifle. I just put the environment and a generic 55-grain bullet into Bushnell Ballistics and got a rough solution for my 370-yard target. I obtained a 100-yard zero then dialed out to what the app said for 370 yards. It was really close, so I adjusted the BC and the velocity a touch to get it where it actually dialing to – 1.7 MRAD. 

From there I got my 500-yard dope, 3.2 MRAD, and dialed out. It was on target.

Between that odd shooting position of the rifle and not using match or precision ammo I wasn’t having the best groups, but they were acceptable and repeatable for practical use and going 5 for 5 on the 2/3 IPSC target (11.5” x 20”) was easy. Wind was light but I was certainly getting some vertical stringing.

I wanted to make sure dialing with this setup not being level-sync’d between the rifle and optic wasn’t an issue, so I dialed out to 9.2 MRAD and used the XRSII’s hold-unders on the reticle to compensate. It was spot on. 

Now, if you look at the IPSC target above as well as the gong you'll notice something: the groups are left-justified. There was no wind the morning I shot for this experiment. Why are they both left justified?

Something about those images bothered me. I asked a friend to take a look at this experiment’s concept and it turns out I missed a factor. Once I pictured the issue top-down in my mind it made sense.

When the scope’s tipped to an extreme like this it actually painted the picture well. When the scope’s tipped that much it means the rifle’s off to the side to make the scope level. This makes part of the sight height over the bore be offset to the side of the bore. Our ballistic apps and calculators don’t account for this. You could, in theory, account for it by measuring how much to the side the scope is offset from the bore and calculate it. I can’t say it’s practical or something we’d really want though. 

To demonstrate it and paint the picture I took a picture of the rifle from above. It has the scope mounted back straight in it, but then I took a second picture with the entire rifle tipped back to where it was for the experiment. In it you can see the centerline of the scope with a red line, and the centerline of the bore in a green line. With the scope aligned level with the rifle it’s directly over bore with no offset. With the scope not level and tipped over you induce an offset. In this case it was probably around half an inch. I also depicted those lines in the image above, in a very exaggerated way, to show them apart at the firing line, meeting at the 100-yard zero, then crossing sides and diverging further apart as the distance increases.

With the scope zeroed out at 100 yards everything was ‘on’. However, that half inch at the firing line with the bore line on the right turns into one half inch at 200 yards on the left at impact. In this case, every 100 yards further means another half inch further impact to the left. Now we know where those left justified groups on the targets came from. 

I wouldn’t consider this experiment to be a conclusive answer on whether or not a scope & rifle need to both be exactly parallel & aligned with each other. I would say that in extreme cases it certainly will matter the further distance you are away from your rifle's zero distance. The reason is that sight height over bore. When the scope’s directly over and aligned with the rifle you can account for that sight height on those close shots where it’s making a difference. If the scope’s tilted and not in a plumb line and is offset it’s going to make that correction be very difficult as it’d need to be corrected for not only on elevation but windage as well. Doing that consistently and on the clock would be very tough.

As for medium and longer ranges? I’d say it depends. Depends on how out of alignment your rifle is to your scope, and the distances you're shooting, and the precision and accuracy you're trying to obtain. I'd also say some may be making a mountain out of the gopher mound on their scope mounting. If your rifle’s off a few degrees from plumb with your scope it isn’t likely going to be the reason you missed a shot. If you're wanting to make it fast & easy get yourself a level mounting kit.

In the end, the most important thing on scope setup is try to get it level and aligned with the rifle the best you can, and get that scope to a position that's comfortable for you. As for the range, make sure that scope's level when you're shooting. That scope absolutely needs to be level and a bubble level can really help here. If you have a scope mount that has a level integrated, you really need to make sure the scope is plumb while that level is indicating level. The goal is to have that scope, and therefore its reticle & turret bores, plumb & level when that shot breaks. The scope was always level when I was shooting in this experiment, and even in this extreme level of scope and rifle alignment - I was still making hits.

Until next time.

-         Bushnell Social Guy

P.S. Yes, I remounted the scope closer to plumb after this experiment.