So in the year 2015 is it still bad to bridge a red dot sight?

[JBecker 72]

It's 2015, rails are continuous and free floating on many rifles. Optics and mounts are robust and have good repeatability when it comes to holding zero. Is it still bad to bridge an optic? It's not like I'm using a cheap optic with a chincy mount and a drop in rail here. What say the experts?

http://i149.photobucket.com/albums/s73/hownowbrowncow_02/Guns/2AF3488B-C8A7-4E7F-84F4-07A7C41097B1_zpse0l2oeic.jpg (http://s149.photobucket.com/user/hownowbrowncow_02/media/Guns/2AF3488B-C8A7-4E7F-84F4-07A7C41097B1_zpse0l2oeic.jpg.html)

[ColtSeavers]

2 joints all right up on each other or one? Personally, I see no need to bridge the gap even before considering possible moving parts/joint conjunctions, especially considering the pressure that can be applied intentionally or otherwise to a FFR.

Honestly though, if it's a quality one piece mount, bridging a properly installed quality FFR and not a rifle that my life would depend on, I don't see why not.


ETA: I still don't do it though, just wouldn't berate anyone else for doing so in the above given situation.

[JBecker 72]

It's a Geissele rail which is an extremely rock solid mount. The optic mount is the Aimpoint QRP2 which is also a very solid design.

My question came from me pondering about all the rails on the market now that are of similar design. They create a continious upper rail section but according to the internet you can't really use all of it. Of course this rule of thumb generally has been around since before rails like this were available. So I was wondering if this is no longer a concern with modern equipment.

[samuse]

If I'd trust the rail to put irons on it, I'd trust it for that.

Would I bridge the gap with a set of scope rings? Probably not, but a one piece red dot mount? Don't think it'll hurt anything if the rail gets knocked around a little.

[JBecker 72]

If I'd trust the rail to put irons on it, I'd trust it for that.

Would I bridge the gap with a set of scope rings? Probably not, but a one piece red dot mount? Don't think it'll hurt anything if the rail gets knocked around a little.

That's pretty much my thought as well. For what it's worth, I can remove the rail from the upper and reattach it and the backup sights holds zero. The way the Geissele SMR interfaces with the barrel but is pretty impressive.

[johnson]

Is that bridging though? I'm not familiar with the QRP but it looks like the clamp is only on the receiver. I thought bridging meant like splitting two mounting points like a dual lever scope mount.

When installing FF handguards I usually eyeball it and make sure that top is flat all the way across or at least centered. Recently I reinstalled a CMR using a riser mount that spanned across the two halves. With the CMR clamping bolts removed, I tightened down the riser evenly and then proceeded to reinstall the CMR bolts.

After everything was done I noticed that 1) the CMR wasn't perfectly flat across the top, it was slightly raised and 2) when I laid the rifle upside down (with nothing installed on the picatinny rails) there was a gap of about 1/16" or less at the front of the rail to the table. I haven't looked further into it but it could've been caused by the slightly raised height of the CMR acting as a leverage point in the middle because of the weight of the lower receiver pushing down on the other end.

The other thing that I noticed was that only the underside of one side of the picatinny rail was flat across (the right side). I never gave it much thought but it makes sense that with this particular riser the CMR was only aligning itself with whatever was clamping against it, and in this case, only one side of the riser.

http://i.imgur.com/KWJfRZ3.png

Picture of the riser. It is two pieces and the whole right side comes off when you loosen the bolts.

http://ecx.images-amazon.com/images/I/31ZMuL35UEL.jpg


After this I realized first hand of the reasoning of why you shouldn't "bridging the gap" and why you should use a cantilever mount or get a monolithic upper if you need to mount a scope more forward for eye relief. Even though there's a standard for picatinny rails, they rarely match up perfectly between receivers and handguards.

[JBecker 72]

Here's the mount from the other side. The cross bolt is on the last slot on the upper receiver. If this isn't acceptable the way it is, an ADM cantilever mount is probably in my future. I like using this optic closer to the midway point of the rifle even though I'm not using a magnifier (currently). Though an Aimpoint 3X in a twist mount would be cool. And with the position the optic is at right now I could fit both easily and still have a folding sight.

http://i149.photobucket.com/albums/s73/hownowbrowncow_02/Guns/33416094-76F4-4013-B22B-A9BF67EF6BEB_zpsicpolqga.jpg (http://s149.photobucket.com/user/hownowbrowncow_02/media/Guns/33416094-76F4-4013-B22B-A9BF67EF6BEB_zpsicpolqga.jpg.html)

[wigbones]

34961

I've got a similar setup where my Aimpoint micro extends just past the upper receiver and the cross bolt is actually across the upper receiver. It's a Geissele rail as well and I have no concern about the way it's set up. Everything is rock solid and flush.

[1911-A1]

I usually mount my optics with one rail space extending over to the handguard as an anti-rotation measure. I've never noticed a drift in zero, and doubt I will with a red dot, but I HAVE had handguards rotate loose, so that's my reasoning.

With 95% of the mount firmly clamped on the upper receiver, there's no reason to expect zero will be affected.

[ColtSeavers]

Looked at pocture in the OP again, was/am wrong, redacted.

[ColtSeavers]

Sorry for the double post, but on a related note/line of thinking, I use an AD-B3 mount to bridge the gap and keep the top rails 'square' while installing/tightening my Free Float Rails and while also thinking of building an iron sight only AR, I wondered about using a Bipod mount or something in the same fashion (to bridge the gap) permantly to keep any excess or possible shifting/rotation at bay.

[Ryno12]

I can't get myself to bridge the gap. That doesn't mean it's not possible, just that I don't do it. I personally think the QRP2 mount is junk (at least mine is) so I certainly wouldn't do it with one of those.
The only time that I will bridge the gap is to aid with alignment when installing a new rail.

[Eurodriver]

Did laws of physics and properties of metals change in 2015? Cool...

[JBecker 72]

No but many manufacturers are advertising how well their rails lock up these days.

[turnburglar]

OP: I think the way your is would be fine.

If I am willing to put a peq and irons on the free float rail, why not trust it for an optic as well? Personally I don't mount optics that far forward but its not because I don't trust my rails. (ALG/BCM)

[samuse]

No but many manufacturers are advertising how well their rails lock up these days.

But unless they're Daniel Defense, Geissele, or LaRue, they're FOS!

[Eurodriver]

In theory, it is perfectly ok.

In practice, there are manufacturing tolerances between uppers and rails and these tolerances can cause problems.

But when you have 2 strong rings on two strong rails holding together what should be a perfectly straight, weak aluminum tube, you can run into issues. This is exacerbated by such things as preloading a bipod.

http://i56.photobucket.com/albums/g165/InfiniteGrim/GUNZ/Vortex%20Viper/IMG_1213.jpg