"Return-to-Zero" Mounts: Fact or Fiction?

[ALCOAR]

This is sorta in the realm of "what it means," such as what it actually means when an optic is tagged as "parallax-free." It's absolutely impossible to make anything in which light passes through glass bo be parallax-free (SCIENCE!). In the end, it basically means that the manufacturer has made it as parallax-free as the physical laws of the universe allow it to be. Like with anything measurable, there's a low end (failure), the desired goal, (threshold) and a high end (objective).

With mounts, what the phrase "return-to-zero" really means is that, when you remove the mount for whatever reason, so long as you remain consistent in your remount procedure (same gun, same place on the gun, same method each time), you should see no more than a .5MOA shift.

If you consistently see greater deviation than that, that's a FAIL.

If you consistently see it meeting .5MOA deviation, your mount(s) has achieved the THRESHOLD. It's good, solid, within desirable tolerances.

If you see it consistently showing devaition less than .5MOA or even NO deviation, you are a bastard and I hate you. Not really, your mount is simply achieving the OBJECTIVE.

Everything is subjective to how drunk the little old lady in the factory is that day, what the QC practices of the vendor in question are, sunspots, and the unanticipated appearance of the Spanish Inquisition. There are vendors that do a good job of of keeping those instances to a minimum. After that, you have intangibles like the differeing intensity levels of Silly-Straw Chromosomes that any given user might have....there are always unaccountable, indefinable variables.

This is why ADM, LR, BoBro, and a few others are heartily recommended. It's not fanboy-ism, it's the fact that there is a measurable incidence of their equipment (with all other things being considered equal) consistently meeting and usually exceeding threshold.

EDIT: For clarity, in most instances, all one'll see on a performance spec is threshold/objective, so anything not meeting threshold is considered to have failed.

I strongly endorse the above reply...straight up pegged it

[SA80Dan]

I've used Bobro for a few years now including a lot of prototype stuff. Got a very tall 30mm one for 3gun on the way to me now. Thus far I have noticed a measurable shift. When I install the scope back on the gun I mount the scope mount on the rail and push it forward and then lock down the lever. With a 1-4x scope I've never noticed it shift.

I do the same with my mounts; whether it be the ADM ones or the Bobro. When I reinstall I always push the mount forward and left, then hold it there and throw the lever(s). No noticeable zero shift with my low power variable scopes.

[JohnnyC]

......and the unanticipated appearance of the Spanish Inquisition.

No one expects the Spanish Inquisition!

Personally I don't trust ANYTHING to "return-to-zero" since there are so many variables that JSantoro so eloquently described. If it happens, great, but I'm NEVER going to pull an optic off a gun, put it back on, and not check my zero, so it's really a moot point. All it's really doing is saving me a couple minutes if it happens to be close, and to be honest it's probably not saving me much time because I'm not going to trust less than a few groups anyway.

In my mind, moot point.

[blackscot]

Thanks for the further replies. Looks like the basic answer is "yes" with some qualifications, both practical and addressing aspects of meta-physical uncertitude.

I'll probably give it an off/back-on-again shakedown at the range where I can carefully evaluate any effect, before deciding to rely on it under less controlled circumstances.

[Mute]

I've used two different Bobro mounts now. One for an Aimpoint dot sight, the other for a scope. Both have been perfectly capable of returning to zero without a single problem. I trust them without reservation.

[jpr8771]

newvie here...wednsday i am expecting my bmc upper to be in and the only thing i couldnt order from bravo company is the rear sight...i want to go cheap so ive decided on the mbus....they were sold out...i need to order up real quick so i can have it in with the upper and be ready to shoot that day.

i dont want to highjack the thread and i didnt want to start another one because im sure my question has been asked before but i just cant find it. so just a quick answer from someone knowledgeable will suffice

question is...will the magpul mbus rear sight work with my fixed front sight marked F...ive ready enought to know that it is higher than normal...just dont want to order and it not work...thanks

[ozarkpugs]

If I'm understanding this I've been using my 5 moa wrong , I have always adjusted it so my pullets struck 6: on a 5 " circle at 50 yds and in the middle at 100 .Centering on a circle the same size as dot and it's easy to tell if re aligned . Of course the Ruger ar15 is better than 1.5 " and I don't ck zero with ball ammo .

Sent from my XT1093 using Tapatalk

[Endur]

I used to remove my optics for cleaning all the time on my issued weapons and those things were not the best mounts made. I never lost zero or noticed any shift.

[abso]

Depends on the mount. I've had a Larue mount lose its hold on the upper receiver and start sliding while it was "locked" down.

I've made it simple on myself. I don't buy QD mounts anymore. I never swap optics anyway (each rifle gets its own), so the main feature of QD mounts is a bust for me. There is only the risk that it loosened up. Even if I did the whole swap optic thing, I'd reconfirm zero anyway. At that point, I'm not sure they are that valuable.

Another advantage with QD is that you can dump your entire optic and us BUS if your optic takes a hit or goes down. IMO that's overblown if you use high quality optics - you can also put offset optic/BUS.

Does anyone know of an actual case where someone ditched their primary optic and used their BUS in combat?

[sol1777]

I think C4IGRANT nailed it. Unless your using a serious precision setup, you won't be able to tell with a standard m4 carbine and optic.