Rimfire Central Firearm Forum banner
1 - 9 of 9 Posts

· Registered
402 Posts
Discussion Starter · #1 ·
A few weeks back, I read a post by Smoothtrigger about the EXD Engineering Vertical Reticle Instrument, and I immediately knew that I had to have one.

The device arrived this past week, and yesterday I double-checked the scope installation on 8 different rifles. As good a job as I thought I had done previously, 4 of the 8 benefited from some minor fine tuning.

I don't know whether to characterize the instrument as simply brilliant or brilliantly simple!

There is no requirement for what one might perceive to be a flat surface on either the scope or the rifle, because the device helps ensure that the optical centerline is in the same vertical plane as the bore by indexing at two points each on the objective bell and the barrel (or less optimally the top of a picatinney rail on an AR that I double-checked).

One simply supports the rifle / optic combination in the vertical as indicated by the single bubble level, and then rotates the scope within the rings to align the reticle with a suspended plumb bob. I chose to do this indoors so as to minimize any environmental influences.

Hopefully most folks appreciate the critical importance of not having the reticle canted with respect to the optical centerline / bore plane when it comes to shooting at variable distances, whether the technique employed be dialing-in or holding over.

Here is the setup that I used in my foyer to support the rifle:

And a slightly closer pic of the instrument on the scope and rifle:

And finally, the plumb bob in my den about 11 yards away from the rifle. I found that using the bright red string contrasting against the black reticle and background worked excellently:

I quickly learned that by slowly sliding the rear of the rifle vise slightly back and forth sideways (while keeping an eye on the bubble level), it was easy to get extremely precise alignment with the string by watching it appear and disappear behind the reticle along it's length. It is a little hard to describe the technique, but hopefully it makes some sense.

While I have been able to do a good job mounting optics over the past three and a half decades without this tool, using the tool makes it very much quicker and easier, and with an associated higher level of confidence in the results.

Of course, while the true test of any optic setup only comes at the range, it is my expectation that any remaining error will be very slight, if at all.

It would be hard not to recommend this tool to anyone who has the desire to easily and reliably mount a scope on virtually any rifle with a high degree of precision.

Thank you Kevin for originally posting about this fantastic tool.

· Registered
402 Posts
Discussion Starter · #10 · (Edited)
A few questions about this system:

1) I don't see anything here referencing the bore. The device then assumes that the bore is (correctly) drilled left/right centered relative to the outer circumference of the barrel. Is this correct?

2) Can this device work on octagonal barrels?

3) Does this device have several inserts for the piece at the front of the scope for different sizes of objective lenses you may install?

This looks like a pretty good setup. I usually have to fiddle with vertical alignment a bit, as the scopes tend to rotate a bit while tightening the ring screws. This may not stop that, but at least it makes a quick check for when you've finished.

Thanks for the review and pictures!
1) Yes, the assumption is that the bore is concentric to the barrel OD.

2) I don't see why the device wouldn't work with octagonal barrels. One of the rifles that I tried it on was an AR-type where the hand guard extends over the barrel preventing direct indexing. I specifically chose a rifle with a monolithic picatinny rail hand guard to minimize the error of the barrel not being centered within it.

3) Since the device is indexing a "V" to a circle (typically), there are two points of contact, and the neither the diameter of the scope objective nor the barrel matters. There is an adjustment thumbscrew to accommodate various objective diameters and scope mounting heights.

· Registered
402 Posts
Discussion Starter · #17 ·
Those instructions are verbatim the ones that were included with the device I received, and the illustrations are identical.

At the bottom of the paper, it says "Copyright 2011 EXD Engineering".

Towards the top of the page is the name "One Hole Groups (TM)", with an address of:

P.O. Box 4408
Lawrence, KS 66046

There must be some sort of connection between the two companies, but the question of chicken versus egg is an interesting one.

· Registered
402 Posts
Discussion Starter · #24 ·
I have tried to buy one, but so far no luck.
It occurs to me in looking at this device that considerable accuracy in manufacture and calibration of the bubble would be required to enable it to perform its' intended function.
Any feedback on this issue from those that have them? Is the slide containing the bubble reversible so that the bubble can be checked? Are the Vs machined evenly and in alignment with the central slot and each other? Is the slide a close enough fit to minimize rotation between the two elements?
Interested in your assessment.
It sounds as though you have a good understanding of the requirements for this instrument. I am an anal retentive engineer, and had many of the same questions which you pose. Here are some observations that I have made in such regard:

If I understand what you mean by "reversible", I would say sort of. It may not be apparent in the pics, but there is a channel milled into the rear of the piece to which the bubble is mounted. The longer, narrower piece rides in this channel. As such, one cannot flip the bubble piece over because the channel is only on one face.

Skipping to your last question, the fit of the narrower piece within the channel is quite precise, and there is virtually zero apparent relative rotation when the thumb screw is loosened just enough to allow sliding. By my caliper, the width of the sliding piece is within 0.001" of the width of the channel.

As to squareness of the bubble with the two aluminum pieces, I compared against a standard carpenter's level, and they correlated well, both the bubble piece, and the sliding piece when secured to the bubble piece. While the bubble piece is not "reversible" relative to the sliding piece, the converse is true. The favorable indication of squareness remains true when the sliding piece is flipped.

The width of the slot in the sliding piece and its squareness are of non-consequence since the indexing is done at the interface of the edges of the sliding piece and the channel of the bubble piece. The width of the channel is 0.070" greater than the diameter of the thumbscrew thread, so there is nowhere close to any contact. The measurement from the edge of the slot to the edge of the sliding piece is within 0.001" along its length on both sides as an indication of general machining precision for this non-critical dimension.

I can't think of a good way to measure the precision of the V-notches other than with my Mk1-calibrated eyeballs, and I wear prescription glasses. ;)

Now, with this all said, we are dealing with bubble levels, which in my mind have an inherent degree of inaccuracy, but they seem to be the generally accepted tool for the job.

As I mentioned in a previous post, the real test comes at the range. Yesterday, I took a new rifle and scope (Anschutz 1727-22 and Leupold VX-6) that I had setup with this tool to the range. After zero'ing at 50y, I dialed in 8 MOA to try at 100y, and the POI was directly above the bull. I dialed down 2MOA, and the POI was on the bull. The fact that the POI was not shifted laterally indicates that the scope and rifle were well aligned. Now, granted this was only 6-8MOA adjustment and was using a bipod without a cant level mounted to the rifle, but the results were as desired.

Hopefully, these devices will come back in stock somewhere soon so that all y'all who have become interested can get your hands on one. I feel like I have dangled a carrot in front of folks, and then eaten it all myself. There is no phone number on the literature that came with the device, and I can't find a website for EXD Engineering. I may give that other company, Long Shot Products, a call to see if they can help. The number on their website is 513.583.9081.

· Registered
402 Posts
Discussion Starter · #26 ·
^^^ If that was directed at me :D

Heres a post I made in another forum yesterday :bthumb:


But first a word about Spirit Levels --

100 years ago my Pappy took me into Grosmans & showed me how to pick out one -- out of 8 or 10 --

The Stanley string level I bought with him lives in a eye glass case wrapped tissue paper -- dead accurate for what it is --

When I buy 4' or 6' levels after I picked out the best out of 10 -- I'll put in on the best candidate to check -- so when I bought the plastic two pack yesterday -- one of them pasted muster --

When I slam a scope on a long gun - my procedure is --

Get the mounts as parallel as I can in line with the bore ( a 2' pipe helps ) -- slide the scope fore & aft for my odd shaped head -- level the barrel side to side & front too back and lock it down in my padded bench vice -- measure the distance between the bore center & scope center -- that measurement goes on a paper -- tack it in the bed room wall - about 25'-ish ft. away -- the laser bore thingy into the barrel -- move the paper so the bottom dot is covered with the red light -- then move the redical to the upper dot ---- this gets me on paper at 50 yrd. --- then at the range I'll tweak it --- works for me --

Soooooooooooooooooooooooo --

Pinky leveled across the receiver --

Then checking the already mounted scope that shot good last month -- *** ?

New hand built toy centers itself the the bore center --

Leveled on the scope -- ( I should have squared the cell over more -- but its good ) --

Looking into the scope centered on a door edge I saw this -- mine was only two line thickness's to one side -- not as bad in this borrowed pic --

So looking at the door edge and through the slot -- its now plum -- the amount of twist I gave the scope was less than 1/32" --

Now her scope is re-set -- no excuses now -- :rolleyes:
I appreciate your ingenuity (sort of), but am not seeing anything that keeps the two pieces of your "toy" square with each other. How exactly does it "center itself to the bore center"?

· Registered
402 Posts
Discussion Starter · #31 ·
No, I am not trolling.

The self-aligning of a V-block on a round object is self evident.

The objective of this tool is to ensure that the optical centerline is in the same vertical plane as the bore centerline, therefore there must be a means by which both of the V-blocks are kept orthogonal with each other.

It isn't apparent how your version of the tool accomplishes this.

No need for you to bother explaining, as this dialog is clearly going nowhere.

Have a nice evening, and enjoy your tool.

· Registered
402 Posts
Discussion Starter · #37 ·
I've read through every post in this thread but still can't see how this device could be of any real-world benefit over two bubble levels double-back taped on (one to the scope's elevation adjustment cap, the other to the pic rail).

"Real-world" being key, mind you.

My shooting buddy and I have been going though the "your scope is mounted crooked - no, your eyeball is mounted crooked" debate for ~30 years and counting. :)
The "real world" benefit may indeed be negligible to some folks.

But consider the example of shooting a subsonic .22LR at 300y, like some of us do. The elevation change from a 50y zero is in the neighborhood of 50MOA (that's 12 FEET of drop). Just a little bit of reticle cant might equal a number of inches difference between the actual POI and the POA, both in elevation and windage.

Here are a few shortcomings of the "conventional" two-level method which this device mitigates:

-A rifle might not have any flat surfaces, and even if it does, that flat surface might not be truly perpendicular to the vertical line between the bore centerline and the optical centerline.

-A scope's turrets may not be flat, and believe it or not, they may not actually be square with the reticle.

This device establishes the line between the optical centerline and the bore centerline as vertical by direct measurement.

Aligning the reticle with a plumb bob also places the reticle in the true vertical; remember that we aim with the reticle when holding over, not the scope's turrets.

Both of these measurements are based on gravity which puts the pure trajectory plane in the same plane as the reticle's vertical indication. External ballistics factors other than pure trajectory such as wind, spin drift, and coriolis effect should be included in one's ballistic solution.

For someone who only shoots at 25-50y in a non-benchrest application, or uses a cheap scope that doesn't track adjustments accurately anyway, the difference may be negligible, but I doubt that most folks intentionally mount their optics canted, and this device facilitates one mounting their optic very precisely with ease and expedience.

Can a scope be properly mounted without this device? Absolutely; the device just makes it easier and faster.
1 - 9 of 9 Posts