DIAMOND BACK 7.5 Inch AR with MBUS Problem

[Skywalker]

Please tell me what I'm dealing with. Took this brand new gun to MAGNUM yesterday and could not get on paper at 25 meters at first. Brought it in to about 10 meters and I think that in itself is to close but that is what I did. Got it on paper and was walking it toward bulls eye and got close. Keep in mind.... I'm on a table with sand bag front and rear so she is stable for sure. I would shot 3 shots at a time. I ran it back out to 25 meters and was all over the place and no way to hit anywhere consistent. At the 25 meter distance my rear was far right and the front post was almost all the way down. I left very discouraged. So, gun is cleaned and I'm thinking I'm doing something wrong but took another approach just 10 minutes ago. Put it in the TIPTON with my sightmark bore sight and from the kitchen table to my garage door thought I would just move the rear only and align that. It's not quite 25 meters but as you can see from the picture it's already far left. The floating hand guard is tight, looks to be straight and perfect clearance around the end or barrel to the naked eye. Please give me some info on where to go at this point. I'm going to put a red dot on her but first like to have these MBUS up and working. Thanks
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[ray1970]

Is black diamond the manufacturer of the firearm? I've never heard of them.

[Skywalker]

DIAMONDBACK FIREARMS out of Florida.


Is black diamond the manufacturer of the firearm? I've never heard of them.

[ray1970]

Thanks.

So, after the ten yard try when you moved back to 25 you said it was "all over the place". So some shots were high, some were low, maybe some left and/or right?

What size was the three shot group at ten yards? It should have been pretty much one little hole at that distance.

[Skywalker]

After moving to 25 meters 2nd time they would be like high left about 5 inch group. I would adjust and I'm talking 1-2 clicks. Shouts would move to say far right and low. When at the 10 meter initial while walking or trying to walk it in the groups were still 4-5 inch. BTW, I have two of these and have not shot this one yet. At the kitchen table doing same thing with bore sight. Have not moved MBUS and looking down pipe and front rear MBUS are not moved from factory and red dot is almost spot on for this same test. Maybe swap sights out on the two guns and see if it stays or goes away on the misaligned pistol.

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[ray1970]

Kind of a hard diagnosis without laying hands on it or putting rounds through it. My best guess would be something weird is going on with the barrel. Maybe the bore is angled or something? Or possibly the front of the reliever is no where near square? Maybe the barrel nut isn't torqued properly?

Smarter people than me might come along and shed some insight on this issue. I have no other ideas. Sorry.

[Skywalker]

Thank you Ray. I'm dealing with the rear MBUS right now. If both sets of MBUS has problem then the gun is the issue.

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[ray1970]

As a quick reference, pull the sights off, use your laser thingy, and eyeball down the top of the receiver/handguard kind of like a shotgun and see how far off it is.

[Skywalker]

OK. Just swapped the MBUS and problem only remained with the one pistol. I'll remove and eyeball now with bore sight only.

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[Skywalker]

Here is the sight picture from the sister or twin pistol.... no problems as I can see but have not shot.
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Here is the pistol that is off with two pictures showing the rails and then just down the top with bore sight projected to garage door. To my naked eyes I don't see anything but I'm betting the slightest bit will be big on the other end. **NOTE** After blowing up the picture from here... I can see the rails are slightly off where they meet. Jay, do you see and agree that is a problem?
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[ray1970]

Lol. I'd say straightening the handguard a bit will definitely help. Looks like it's clocked a fair amount to the left side. I'd fix that and try again. I bet you'll get better results.

[Skywalker]

Thanks for the help Ray. Just a little conversation goes a long way.

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[ray1970]

No problem. Shouldn't be a big deal to reclock it either. Just loosen the jam nut right behind the handguard, rotate the handguard, and lock it back down. Having some sort of scope mount or something similar to clamp the top rail and handguard together makes lining it up and keeping it lined up while tightening the jam nut easier.

[Skywalker]

Sounds good. Just watch a video on a diamond style Yankee hill install and be used a scope with dual levers to do just that. I've never done it but to have a Weaver AR tool kit. Should be doable and greatly appreciate you.

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[Skywalker]

Didn't have the tool to remove this collar so off to Springs Armory this morning. Fixed and perfect to include a new Velocity 3lb trigger. Sweet. Now another for her twin. Trip to MAGNUM soon!

[archangel]

Did you resolve the problem I had the same problem my rail was not tight enough I put some lock tight on the screws that go into the barrel nut and that fixed the problem for me

[Skywalker]

Didn't use loctite but she is spot on now. If it moves, I'll put some in and thanks for asking.

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