Ro rib advice

I bought a rib from rock river last year to eventually have mounted on y RO. It’s aluminum and does not have the slide racker built in.  I want to keep the sights on my RO so I had the rib milled to clear the front sight as well shortened to clear the rear sight.  This being said I will have a total of 3 screws holding it to the slide. I have seen this done but also think those ribs may have been steel.  Does anyone see this as being a problem with the aluminum one I Have?  I think KC does this as well but again not sure if the rib is stell or aluminum. Look forward to any feedback.  I checked rock river sight and also noticed they don’t seem to sell the aluminum rib anymore which also concerns me.

Thanks in advance

3 is fine. I do this setup regularly. Just make sure threads are clean before using blue loctite. 
Jon

Can't help with the solution but would sure like to see some pics.

RRA SCOPE RIB ITEMS # PS1427 & PS1428 ARE ALUMINUM. JP

Jon may want to weigh in on this. I've had two mounts with broken screws, one was a Red Bluff frame mount, the other a Clark slide mount. If I recall correctly, both had threads that were too fine.

99% of slide mounted scope rails use (4) #6-40 screws. The screws act in tension pressing the rail into the slide which now has a friction force between the slide and rail. They also function in a shear capacity. The only time I have seen them fail is when the mount has been loose and continued to be shot. I have used (3) screws in the past for this exact setup succesfully. Yes taking away a screw loses 25% of the tension/shear capacity. 
Another screw can be added or modifying mount to #8-40 screws can also be done. Or allowing the mount to rest against the rear sight as a stop can help. More than one way to skin a cat!
Jon

I prefer to have 4 screws in my base 2 of them on either side of where the clamp screw on the ring is. But that's me and I make my bases using 7075 aluminum. One important thing to understand is that no matter how many screws are used the tapped holes in the slide must be exactly on the same center distance as the holes in the base. A drill press is not good enough, a milling machine is required and will locate the holes within .005" of true position. I use a Jig Borer that will locate the holes within .0001" but a little over kill. If the holes are not at the same center distance they will tend to come loose. Loctite will not help because it's not the screw turning that's causing the loosening. Furthermore if a milling machine is used a 4th hole can be made in the base and magic marker used to color any silver though most will be covered by the screw. Browells also sells aluminum touch-up.

I agree with Froneck. The holes need to be properly located.

I've been running 3 screws in my rail forever--nothing fancy, the same beat up screws.

Twin RO with 3 screw mounting.
Jon

Froneck wrote:I prefer to have 4 screws in my base 2 of them on either side of where the clamp screw on the ring is. But that's me and I make my bases using 7075 aluminum. One important thing to understand is that no matter how many screws are used the tapped holes in the slide must be exactly on the same center distance as the holes in the base. A drill press is not good enough, a milling machine is required and will locate the holes within .005" of true position. I use a Jig Borer that will locate the holes within .0001" but a little over kill. If the holes are not at the same center distance they will tend to come loose. Loctite will not help because it's not the screw turning that's causing the loosening. Furthermore if a milling machine is used a 4th hole can be made in the base and magic marker used to color any silver though most will be covered by the screw. Browells also sells aluminum touch-up.

Has anyone tried a properly fit dowel pin (I'm another Jig Borer guy) or two to locate the rail so the shear load is not on the screw shanks?

I am gaining interest in this sport/hobby and just thinking out loud, as I am considering installing a rail on my 1911 slide.

Thanks!

Dowel would always be nice, but not necessary. There are pistols running around with 100k rounds through them with just screws holding the mount on.
Jon

DA/SA,
That would be how Nelson ribs are attached. no reason you shouldn't do it if you have the equipment, time, etc.

If your going to cut your rail up anyhow then I prefer the Weaver number 26. They come with bigger screws and are priced 1/4 cost ($10.00ish). I cut the rail slot with my band saw and don't have to mess with front or rear sights. I suppose I should use the aluminum black but it wouldn't change the way it shoots.

This certainly works, and I've used the Weaver 88 with some milling to accomplish the same thing.  What the slide rail mounts made for the purpose give you is the 1 degree draft that better aligns the scope with the barrel in lockup. Most red dots have enough elevation adjustment that this isn't required, but it is nice for zero to be somewhere near the center of the adjustment range.

Thanks for the info guys

Giles milled the GI/Colt rear sight as a key, milling it to the correct shape and milling a cut in the steel (in those days we wanted weight)  rib to fit the modified sight. The rib was screwed in place w/ 2 flat head screws. These were peened in the screwdriver slot to eliminate movement. Professional!
Ron Habegger

Back years ago ribs didn't have a scope attached to them.
I really don't think dowels are necessary though dowels will of course be better. Flat head screws will locate and keep the base from moving using the 82 degree angle. However the tapped hole will have to be at the same location as the holes in the base. If not the screw will contact the 82 degree countersink on one side. Eventually the aluminum will creep (steel will too but will lake longer) and the base will have movement and after a while the movement will cause the screws to impact the holes and increase movement. Eventually the screws will shear off. If I were to install a base having only a drill press I would use button hex head screws, that way I wouldn't have the screw contact the countersink off center. Then after assembly drill and ream two holes for a dowel pin, doing it that way the dowel pins will anchor the base in one place and the screws hold it down. Drilling and reaming the hole after assembly will have the holes in perfect aliment though not in perfect location.

Make sure to ask for the “full coverage” RRA rib.  It will cover the rear sight gap on the RO.  This is not what you will get if you order off the website.  You have to call and ask for it.

On mine, I did the swap out for #8 screws, which was very easy, just had to drill out the rail holes a bit.

  I also used a repurposed and modified EGW slide racker as a dovetail filler.  I then drlled and tapped through it to be able to use that fourth hole.  This was a major PITA and would not likely do it again.

I think what I will do next time is use the rear sight as a stop block for a cut down rib the way I have seen here.  This is such a good, simple idea.  I like it.

But I do have a Weigand frame mount I keep thinking I will try one day....

Contacted KC. yea it’s headed to him to install th RRA cover up rib and have the irons removed. Why play around right!