Cross bolt is not in between rail sections.
Your optic mount has a cross bolt that should be sitting in the gap between rail sections. Loosen the optic mount clamp, and push the optic forward and rearward until you feel it “fall” between the rail sections. The re-tighten. Good to go.
So we now know the mount is out of spec. Can you call the company that you purchased it from and let them know you tested it on another rail with the same results?
[ol]
[li]Ask for a replacement?
[/li][li]Send the bad one back to the mfg?
[/li][/ol]
Can you take some pics (front, rear, underneath, each side) of the Aimpoint and mount outdoors in the shade using your DSLR or PNS camera on “MACRO” (flower) setting?
Been asking for pictures since day 1. This will help confirm the problem that he already solved.
Compare the mount with the pics here…
http://www.skdtac.com/Aimpoint-PRO-Patrol-Rifle-Optic-p/aim.310.htm
added better pictures with more angles
I did at first they seemed helpful and were interested in helping and suggested if I could find another AR to test it on. Well I did and same results so I called the company back again and they got cold on me saying I’m prob installing it incorrectly and to take it to a gunsmith so I can get confirmation on what the problem really is. Im not a rocket scientist here but it appears to be a bad mount. Even in the last pic I posted on how the rear sight sits flush is how I would like the aimpoint mount to sit.
Should I shoot aimpoint an email and see whats up?
Ive been looking at larue LT150 mount unless you guys have any other ideas. Thanks for your help
Contact Aimpoint and send pic’s. It’s good for them to correct this before it blows up into a post like this because a re-seller is dragging his heals supporting their product.
Here’s a problem I see.
This series is made from a detail of picture #11 in post #1 of this thread:
The red line in the picture below is aligned with the part of the 1913-compatible mount designed to fit in the lateral “grooves” of the upper:
In this next picture, the green lines follow the outside of the shank of the mounting bolt, with the yellow line as its center. Important to note that the yellow line does not pass through exact center of the “floating” part of the mount, but rather is biased toward the top. The “floating” part is intentionally made this way, and the next pictures show why.
The reason for this is that the "floating part of the mount is rotated 180 degrees from its proper orientation about the axis of the mounting bolt. The next photo (admittedly poorly photoshopped) shows what it should look like after the “floating” piece is flipped about.
In this last photo, the added dark red line shows the “widest” part of the mount, with both the fixed side and “floating” side aligned, and the laterally-interfacing section aligned with these as well. The light red line shows the narrowest part of both that clamp below the rail on the upper aligned as well.
Summary: I don’t think your mount is defective. The loose piece on the mount closest to the screw-head is upside-down. Flip it over and try again. 
Also, the other angles from the pictures in Post #1, after closer inspection, seem to support this theory.
Bingo…
I can flip that piece 180 and it doesn’t change the way the mount sits on the rail. However, I do find that if I try to mount it with the knob tightened a little too much it can end up not sitting right.
If you haven’t done so, try loosening the knob as far as it will go. (It shouldn’t come off.) With that piece out of the way, try rocking the mount on to the rail, making sure the top of the mount and fixed side are completely engaged inside one of the picatinny grooves. (Wiggle it around a little bit to be sure.) Hold it in place and see if the rail meets up nice and flush with the top of the rail, and see if it’s still ‘off.’ If it is, your mount may not be assembled nice and squarely, or it could just be defective, of course.
If it does look right, tighten the knob, making sure the loose part of the rail-side-grabber piece meets up properly to the rail as you do. Check alignment again.
I put mine straight in to an ADM mount when I received it, so I didn’t have much experience with the QRP until I saw this thread. I took it out of the box to dink with it, and it isn’t too hard to make it not sit right. Of course, yours could just be screwy, but that’s my $0.04 (adjusted price for panic buying inflation 
)
I also did this and didnt notice a difference. You can tell before tightening it that its not going to mount properly. Do you notice a fitment difference between your ADM and the QRP?
I sent aimpoint an email and going to see what they say. From the looks on their site it states turn around time for warranty is 3 weeks.
The ADM hooks up a little easier, more ‘positively,’ I guess I’d say. If I am working the QRP a little sloppy, I can get it to mount improperly pretty consistently. The ADM seems to grab the rail right off regardless. I went with the ADM (LaRue and Bobro were not available at the time) right off after handling a PRO and asking the opinions of others of the QRP. No one had problems with the mounting, it was just that the knob stuck out a little too far for my comfort.
I haven’t tried a Bobro for an Aimpoint, but I have one on another optic. It’s mounting/lockup is really nice, with no adjustment needed on the QR lever for ‘just right.’ The ADM took a couple of ‘too tight, too loose’ experiments to find the best QR lever adjustment where it was easily removed one-handed, but not to where the zero wasn’t stable. The ADM works great, but I would have gone with a Bobro if I could have. I’ve heard the LaRue mounts are great as well, but no experience here.
I just came across this same issue and found the culprit - it’s the lousy Aimpoint mount.
I had the Pro on a BCM 14.5 middy with a FSB and a KAC 600 micro rear BUIS and I never noticed the issue, though I wasn’t looking for it either. I just changed the upper to a new BCM BFH 16" Mid Length ELW (which I really like) and with a Troy front BUIS in place, I immediately noticed the problem. My search for answers led me to this thread.
A couple of observations;
While both the KAC and Troy sights fit the rail perfectly, the Aimpoint mount does not - it seems to grab the rail high as if the mount isn’t machined deep enough for it to 100% engage the edges of the rail.
The larger issue is the way the 3-piece mount made up of the base, spacer and upper ring assembly sandwich together - it you look at the assembled mount from either end, you will see the pieces don’t lock together in a way that prevents rocking from side-to-side with the screws loose. When the screws are tightened, the sections to fit together unevenly resulting in some cant. I did some minor file work on the spacer section to make it lock together evenly and the sights are now almost perfectly centered in the scope.
So the Aimpoint Pro is a great sight that comes with a not-so-great mount. I’ll sight-in the new upper using the Aimpoint base but I will be ordering a Larue or Bobro to replace it.
Could it be something as simple as the clamp part of the mount is upside down? Sometimes those things get spun and if the mounting hole is off center, it won’t fit right. Can that tab be spun 180 degrees and see if that fixes the problem?
I gave that a try to no avail. The base sits flat on top of the rail, its the “sandwich construction” of the mount and the fact the pieces don’t lock together squarely.
So other than Larue and Bobro, what are the top mounts for the Pro?
Luckily, its a 30mm tube, so there are a lot of decent options out there. You’ve got two of the best in mind, also American Defense has a 30 mm QD mount, Midwest Industries, Yankee Hill, I’m sure makes them. You have a plethora of choices and the AD seems to be the bang for the buck mount right smack in between budget and wine & cheese. Enjoy the hunt!
Thanks Joelski!
I’ll take some photos this weekend to illustrate the issue with the mount. I did not take any “before” photos but once you see in the photo what I’m talking about it should be clear. I spent some more time working the mount and the pieces now fit and lock together nicely, and the dot moved considerably in relation to the iron sights once I was finished. It seems pretty solid now and may actually be good-to-go, first range session with the new upper and reworked mount tomorrow.
I just saw this was bumped, and I have some additional experience with another mounting option: I have my PRO in a Larue canted mount (LT129) now, it works really well. It also has a compartment for a spare battery, which is a nice feature. It’s a great setup, but it’s going on my son’s rifle. He’ll be adding a magnifier so the canted unit works out well. I still have my ADM mount too, it is now hosting a COMP M3 on my ‘#1’ rifle. I think I prefer the ADM mount more, mainly because of the locking lever. No ‘real’ reason, just simple preference of how they lock.
jett66, changing out the mount is IMO the way to go.
FWIW, the mount that comes with the PRO weighs 5.4 ounces once the spacer is added. I’ll keep using mine until this one becomes available;
https://scalarworks.com/shop/optic-mounts/ldm-pro/
That will make the weight of the PRO with mount 9.6 ounces.