Quick Release-Two AR's-Same Scope-Same Zero?

[dart368]

Sorry if this is a stupid question, but I have a Trijicon Accupoint scope mounted on my upper which has an 18" free floating barell with a Miculek comp. My other upper is a 16.5" flat top M4 set up.

If I get a quick release so I can switch the scope between the two, am I safe to assume that the zero will be completely off?

[MaceWindu]

If I get a quick release so I can switch the scope between the two, am I safe to assume that the zero will be completely off?

No and yes.


Mace

[dart368]

It won't work then?

[armygunsmith]

There are so many variables, it would be impossible to tell without actually doing it. The zero will change even if you dismount the sight and put it back on the same rifle. I suppose you could zero the sight to one rifle and figure out the Kentucky windage when it is mounted to your other rifle.

[dart368]

If it changes when I dismount it and put it back on, then changing it from one to another back and forth will do me no good. thanks for the answer. :-)

[fcr]

I just used my T-1 zeroed from one upper to another today and it was off.

[SlowArrow]

That might depend a bit on the mount you use.....the LaRue mounts seem to come back to zero very well on the same gun - for a gun to gun transfer it would depend on the differences between the guns.

[maxicon]

It depends on 2 things (assuming a good scope) - the mount's return to zero, and the differences in geometry on the two uppers.

Most quality lever quick release mounts have a pretty good RTZ - under 1 MOA - if returned to the same slot. This is because the lever assures that it's tightened pretty close to the same each time. You can also get good results with quality non-QR mounts if you use a torque wrench.

Whether two rifles will have the same alignment of rail to bore is dependent on a lot of things, particularly how tight the specs are on the upper, barrel, and barrel mounting hardware, but also including barrel and crown quality, twist rate, length, etc.

To figure it out, you have to test it.

An easy way would be to shoot a 9 or 10 round group with rifle A, then shoot 3 x 3 round groups, removing the mount and re-installing it between each set of 3. If both groups are similar, your return to zero is likely good (though you should really do this 10 times to get solid data). What mostly counts here is group size.

Then switch the mount to rifle B and shoot another 9 or 10 round group without making any adjustments. This will tell you how close the geometric relationship between rail and barrel is between the two uppers. What counts here is whether each group has the same center relative to the aiming point.

[dart368]

thank you for your input guys.

[devildog999]

It could go either way.


What you could do is dial all the way to one direction and then count the amount of clicks it takes to get windage and elevation to the other side. Then cut that in half to get how many clicks to get to the exact middle. From there, zero your rifle but keep track of how many clicks you dialed.

If you dialed 5 to the left and 3 up, write it down. Then click back 5 to the right and 3 down; putting you back in the middle of the dial. Then zero for the other upper and do the same. Now you know how many clicks from the middle of the dial to have the zero for each rifle

[9-12]

If you go with a Bobro mount, your POI won't change on any one rifle. Even if the rail is out of spec. You should be able to zero on one rifle, then zero on the other, and simply record the difference. With a LaRue, or any other throw lever type mount, you may have to compensate for any variation in the rail machining between the two rifles. This is where the Bobro mount shines...it'll work on a 1913 mil spec rail, out of spec rail, even on a Weaver rail, all without adjusting, and it's return to zero is point on, every time.

[dart368]

I put my accupoint on my other ar and the zero was way off. I see what you mean about compensating and adjusting. Thanks.

[Ballistic043]

the eotech i sold on here about 3 weeks ago. i sold it to a guy with an AR similar to mine, and when he mounted it, the sight needed no calibration what so ever.

now, the odd thing about this story is; my real AR was not the last rifle the eotech was mounted on. right before i sold it, the eotech was calibrated for one of my airsoft rifles to about 15 feet.

when i sold the eotech i kind of forgot. but i didnt think it would matter since hes probably gonna re adjust it anyways. well when the buyer took the eotech out, and mounted it, he didnt even have to touch the dials. at 30 yd he was hitting the steel target every time!

i knew eotechs were good at rZo but i didnt think that would happen. probably a fluke

[dart368]

Funny thing about what you said about the eotech...I did the same thing...moved my eotech from my 16" upper to my 18" free float upper and it was only off by about 2 inches at 50 yards. My Accupoint, going from my 18" barrell to my 16" was about a foot off. I didn't even bother...I promptly switched them back.