Vulcan Surfaces aka Level Level Level Leaves Offset Error

Finally have my scope vertically stacked with Vulcan’s barrel, but discovered that you can’t trust anything on the gun or scope to be actually level.

I had naively used the tactic of the Level Level Level. That makes you think you got things aligned when the sprit levels are all “level” on the scope turret, the gun and the reticle is vertical. That turned out not to be enough, because not only do things need to be level, but the scope needs to be parallel and centered side to side with the barrel. Otherwise, the scope will be offset to the side of POI except at one zero point (the collimation point).

This diagram shows how the offset becomes a problem that worsens beyond the zero point. I calculated that just a 2 degree error with our high mounted bullpup scopes translates to nearly 1/2 inch POI error at 4 times the zero distance. It’s not huge, but why leave a system error when it can be reduced? This isn’t cant error. You can be Level Level Level but still be offset.

I got a Vertical Reticle Instrument from Brownell’s

It works by centering itself over BOTH barrel and scope. The level on the instrument reads level when the scope is actually centered left/right over the barrel. The machining was far better than I could make and I verified their level with a plumb line.

You tilt the gun left/right until the VRI shows the scope and barrel are stacked vertically. That is the position you keep as “level” for the gun. From there, you rotate the scope to get its reticle vertical (or even more accurately its vertical tracking vertical, but I’m not that good). Lock the scope down with its reticle vertical and the VRI still indicating barrel and scope are correct.

Once done, I found not a single surface on the scope or Vulcan reads as level when things are actually aligned correctly. Everywhere there was 1-2 degrees of tit on what one could have naively assumed as correct if one relied purely on levels. The turret cap, the barrel cover, the breach block, the mounting rail — none were level or agreed with each other.

Without the VRI, getting things Level Level Level would actually induce an offset mount. Now if my rings were machined exactly right to remove all errors of the mounting rail and other parts of the Vulcan, Level Level Level might have also avoided an offset error, but my rings aren’t an exact match.

The VRI revealed the error and made it very simple and quick to get things actually aligned correctly.

Tips:

1. Remove your scope’s lens caps. The scope ends must be ROUND.

2. Put the Vertical Reticle Instrument on the scope and barrel with its set screw loose. Then tighen the set screw. If you do it right, there is only one position the VRI “locks” itself into place.

3. As you tighten down the scope, the distance between the barrel and scope decreases and can shift the VRI. That can fool you into thinking the gun shifted. You may need to loosen the VRI’s set screw to let it settle back into position

4. If you only check the front of the scope vs the barrel, there is the chance that only the front of the scope is centered over the barrel, but not the back. This is worsened if you have one of your mounts flipped around instead of both the same direction. You can check if the scope is also L/R parallel with the barrel by getting the VRI to read centered in front, then putting it on the back of the scope and verifying that things are OK on that end as well relative to the vulcan’s barrel cover.

5. Once the VRI reads level, and the scope is secured with its reticle level, you can adjust your anti-cant device to also read level. Do this last.

Overall, I give a big thumbs up to the VRI for showing me I can’t trust any surface of the Vulcan or scope to be level when the scope, barrel, and reticle are all in their actual correct relationship.