Bobro Mount Positions: Extended vs Sightly Forward

[FourT6and2]

I see photos of people's ARs that have extended cantilever mounts—like Bobro—but mount them farther back on the receiver. What is the point of doing this rather than going with the "slightly forward" version that is cantilevered, but not as much, and mounting it farther forward on the receiver? The optic is effectively in the same position in both cases. But I was wondering if there was a reason to go with one over the other in this scenario. Other than maybe... the extended offers you a little more adjustment should you want to move the optic farther away from your eye in the future?

[GH41]

What mount is needed will be determined by cheek weld position, required eye relief of the scope, and the distance between of the scopes eyepiece, turrets and bell.

[FourT6and2]

What mount is needed will be determined by cheek weld position, required eye relief of the scope, and the distance between of the scopes eyepiece, turrets and bell.

I understand that. But that isn't my question.

If you took the same scope with the same cheek weld, the same eye relief—the same distance between the scope's eyepiece, turrets, and bell—and mounted it so it lines up where you need it on an "extended" cantilever mount, but the mount happens to be in the middle of the receiver, and then took the "slightly forward" mount and mounted it at the very forward edge of the receiver, the scope would be in the exact same place. It is the mount that has moved.

My question is, why would you choose one over the other? Again... the scope has not moved positions. The mount has moved underneath the scope.

This situation means the extended mount is too far forward for the scope in question. So you'd mount it farther to the rear. And the slightly extended mount puts the scope too far the rear, so you'd mount it farther to the front. In either case, the scope itself has not moved.

[markm]

Are you talking scopes or red dots or both?

In the case of Red dots... someone may simply like the Bobro QD mechanism, but may not prefer the Sight to be forward as much as the Bobro can position it.

[Slippers]

This situation means the extended mount is too far forward for the scope in question. So you'd mount it farther to the rear. And the slightly extended mount puts the scope too far the rear, so you'd mount it farther to the front. In either case, the scope itself has not moved.

There's more than a few reasons you see this. When purchasing your first mount, you might not know exactly which mount to buy. You choose what you think is ideal based on some experimentation with holding a scope over your rifle, trying to approximate the best position for the scope's eye relief. It's a pain to return things, and it doesn't hurt anything to have an extended cantilever mount and not run it at the forward edge of the upper receiver, so you might just keep it and use it as is.

Another possibility is that a person may have had a particular mount for a long time but changed to a different scope with different eye relief. Rather than selling a perfectly good mount, they just position it for the proper eye relief.

In the end, it doesn't matter where you place the mount on the upper receiver, as long as you get the proper eye relief.

[FourT6and2]

There's more than a few reasons you see this. When purchasing your first mount, you might not know exactly which mount to buy. You choose what you think is ideal based on some experimentation with holding a scope over your rifle, trying to approximate the best position for the scope's eye relief. It's a pain to return things, and it doesn't hurt anything to have an extended cantilever mount and not run it at the forward edge of the upper receiver, so you might just keep it and use it as is.

Another possibility is that a person may have had a particular mount for a long time but changed to a different scope with different eye relief. Rather than selling a perfectly good mount, they just position it for the proper eye relief.

In the end, it doesn't matter where you place the mount on the upper receiver, as long as you get the proper eye relief.

Thank you.

Even if it isn't an issue, would the shorter mount offer more support to the scope compared to the extended design since it isn't pushing the center of gravity out over thin air?

[Slippers]

Thank you.

Even if it isn't an issue, would the shorter mount flex less under recoil than the longer, more extended version? I would presume so, since it has more material supporting the scope, rather than being suspended out over nothing.

Two things:

1. The majority of the force imparted by the recoil is along the same axis as the barrel, so it's not like the cantilever is being sprung like a diving board.

2. The scope is clamped to the mount, so the strength of the scope is acting in concert with the mount, making it even more stiff.

Nothing to worry about.

[jerrysimons]

BOBROs are stout, no worry of flex.

So I ran into the exact problem you mention. My Vortex 2.5-10x32 is mounted in a BOBRO extended forward. With its eye relief and my shooting 3 clicks out on the stock, it is fine on my AR 15 to just shift the mount back on the receiver. But when I went to put the scope on my MWS as a loaner, I could not get the it far enough back on the receiver rail to give me proper eye relief due to the Knights off-set micro mount taking up the rear 3-4 slots of the top rail and the length of pull of the LMT DMR308 stock. Having this problem is gear and shooter dependent, each scope has different eye relief, each shooter different sizes and positions, each gun different stocks and sights. You will probably be fine with the extended but it is possible to be too far forward. If I could buy again I would have got the slightly forward mounts. YMMV

[FourT6and2]

BOBROs are stout, no worry of flex.

So I ran into the exact problem you mention. My Vortex 2.5-10x32 is mounted in a BOBRO extended forward. With its eye relief and my shooting 3 clicks out on the stock, it is fine on my AR 15 to just shift the mount back on the receiver. But when I went to put the scope on my MWS as a loaner, I could not get the it far enough back on the receiver rail to give me proper eye relief due to the Knights off-set micro mount taking up the rear 3-4 slots of the top rail and the length of pull of the LMT DMR308 stock. Having this problem is gear and shooter dependent, each scope has different eye relief, each shooter different sizes and positions, each gun different stocks and sights. You will probably be fine with the extended but it is possible to be too far forward. If I could buy again I would have got the slightly forward mounts. YMMV

What I might do is buy both the extended and slightly forward and then see if I can return the one I don't wind up using. Or, the Bobro mount is multiple pieces, right? Base, lever (not the QD lever, the cantilever part), and the rings. Three different sections. Could you not just swap out the cantilever?

[uffdaphil]

I shoot nose to CH so bought extendeds for my 1-4 & 2-12 out of concern base might not be able to be mounted far enough forward using slightly extended to get enough eye clearance. Sure enough, properly positioned for me, even with the extended, there is only one available forward slot without bridging the rail gap.

Assuming the slightly extended has more than a one slot reach difference, it would not work for me at all. But the extended still has three slots rearward adjustability which would put the eyepiece even with the rear edge of the CH. That seems enough for all except the ape-armed among us. So the extended will work for the majority of shooters while the slightly for a more narrow group. Or is my logic faulty? I'm partly basing this conclusion on photos of 1-4s showing almost all mounted forward of the rear edge of BUIS.