Attn: Gunsmiths - ***UPDATE*** Need advice on shoddy Bo-mar rib install

Forgive me if I sound irate, but I am. I just had a Bo-mar rib installed on a milspec slide by a local gunsmith (has been in business over 50 years) only to be disappointed. The gun is intended to be a dedicated wadgun for police matches and leagues I am in that are iron sights only. Today, I returned the slide for him to make it right and he gave me attitude and asked what the big deal is. 

The issue:
I gave him a milspec slide, new old stock extended sight bomar rib, and new socket hex head 6x40 screws from a new RRA scope mount purchase. In return, I received the slide with flat head screws attaching the rib, which is somewhat OK, but upon looking at the underside, the screws do not appear that they will sufficiently hold the rib, I roughly measured, while angry, to be 0.1" shallow (see pics below). When I returned the slide today and spoke with the smith via phone, he says the socket heads were ugly and he did not have 6x40 threads so he installed 6x48 flat head screws, stating something to the affect that customers don't know the difference/care. 

On principle, I would think that if you, as a gunsmith or any kind of business, received these items and did not have the proper tools, you would at least CONTACT THE CUSTOMER FIRST! I thought that I would give the local business. I would have even accepted, sorry we lost the screws and installed these, I will make it right. Instead I got, whats the big deal, I guess I can try and find some socket head screws. I rapidly returned to the shop and took the slide back.

I am now concerned that 1) the screws wont hold because they are shallow, 2) the flat head will shear/strip when I need to remove the rib, and 3) apparently the socket head screw is not available in 6x48, thus making it difficult to remedy. I know know better, and to send it to specialist gunsmiths. I figured this was a simple task and not function critical. This rib has a flat spot to somewhat accommodate a gold cup.  Upon viewing the  slide from the front and back, there is a gap. I previously asked if this was going to be an issue on the bullseye facebook page and was told I will be fine. But now with the screws so shallow and that gap????????

Is there hope? see below thank you

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I AGREE WITH YOU. YOU TOLD HIM WHAT YOU WANTED. PROVIDED HIM WITH THE CORRECT SUPPLIES. I'D BE PISSED OFF.

ON A SIDE NOTE I FEEL YOU PAIN .
I AND A FRIEND HAD .45 PPC REVOLVERS BUILT BY A PPC SPECIALIST. THEY WON'T HOLD A B27 TARGET CENTERS AT 50YDS. BUILDERS RESPONSE " I DIDN'T GUARANTEE HOW WELL THEY WOULD SHOOT". AFTER MANY CONVERSATIONS THEY WERE RE BARRELED. SHOT BETTER BUT STILL WON'T HOLD 10 RING  ( ON A B27 THE 10 RING IS 3"WIDE X5" TALL). 2 YEARS IN THE WORKS AND THEY ARE GOING BACK AGAIN. I FEEL YOUR PAIN.

You could get longer screws to get full tension out of the slide/screw set up with the 6-48's. Or you could have rib machined to accept 8-40's and re-tap slide to 8-40 threads. I don't think the gap is an issue with proper screws.
Jon

What John Eulette said.

Also, I know a lot of folks like socket heads, but I have see more socket heads made round (that I have to machine off to get rings or bases off) than I have with old-fashioned slotted screws in the #6-48 size.  Add to that the fact that for small screws, a well fit screwdriver with slotted heads will put much much more torque on the screw than is needed. (A good Smith will have them line up with the axis of the bore, fore-aft)

-ron

Agree with Jon.  Gap should not be an issue, but screws need to go all the way through.  I'd actually prefer 6-48's to 6-40's because you get slightly more thread in a thin section like the slide.

Longer screws

Greetings,

I have repair jobs like yours in the past. Not a pleasant task.

However, Brownells may have the 6-48 socket head screws.

http://www.brownells.com/gunsmith-tools-supplies/small-hardware/metal-screws/socket-head-scope-ring-base-screw-kit-prod622.aspx

Give them a call to verify. These might be specific to the scope mounts and not fit the Bo-Mar rib.

Cheers,

Dave

6-48s are readily available .. I prefer and only install Torx heads.. Socket heads will strip out .. I am also an 8X40 advocate. I have seen many sheared # 6 s but never a sheared #8  .. I just bought a 1950s vintage Remington 788 in .222.. From the factory it is drilled and tapped for # 8s..
I would never consider a slotted drive head screw..The screws should be within .010/.015 of the inside of the slide for maximum thread contact....Are the bolt holes on center..?? Also I am an advocate of at least 4 screws.. Not 3.

Always loved that 788.

Jerry Keefer wrote:6-48s are readily available .. I prefer and only install Torx heads.. Socket heads will strip out .. I am also an 8X40 advocate. I have seen many sheared # 6 s but never a sheared #8  .. I just bought a 1950s vintage Remington 788 in .222.. From the factory it is drilled and tapped for # 8s..
I would never consider a slotted drive head screw..The screws should be within .010/.015 of the inside of the slide for maximum thread contact....Are the bolt holes on center..?? Also I am an advocate of at least 4 screws.. Not 3.

Holes appear to be center, there are 4 screws. The rear 2 screw holes do not enter into the firing pin hole as they appear in other guns that I have ( at least the rear most one). How easy for you or a competent person to re drill and tap for 8/40 vs the 6/48? I just cant get over how shallow those front 2 screws are in. and upon re-measuring that depth it was half way between .1 and .095 the inside of the slide. not sure how thick a top of a SA Milspec slide generally is?

The reason for the gap is to get a firm contact at the edges economically.  Otherwise the rib and slide would have to be matched exactly.  As for the screws, Brownells sells hex drive 6-48 screws.  As to the size 6 vs 8, it came from the factory with 6s.  One can assume that The factory knew what strength they needed.  Lots of these were installed with 6s and held up fine.  The screws will develop full shear strength with engagement of 5 threads, in this case about .100 engagement.  

But you do have a right to have an explanation without attitude.

Wobbley wrote: The screws will develop full shear strength with engagement of 5 threads, in this case about .100 engagement.  

 Just to clarify, because I'm not a machinist nor should I be, there is .1" of "non" engagement so to say. I do not know how much IS engaged since I do not know how thick the slide is, and i do not want to unscrew because I know I will strip the flat head slot.

The reason I questioned the c/l is the photo showing the light and the gap, it appears the rib is canted. Is it? Because that presents another issue.

Jerry, can you tell from the middle photo?  It looks like the rib overlaps the ejection port by a small amount.

Order the screws you want and change them out. While you're at it, use some 5 minute epoxy between the rib and slide. A little on the screws as well. It'll never come off from use and a little heat will break down the epoxy should you ever want the rib off the slide.

6X40 is not a standard "gun size" screw thread - 6X48 is. So really he did it "right" by gunsmithing standards. This seems to be a communication problem rather than a mechanical one. I hope it all works out well for you in the end.

Jerry Keefer wrote:The reason I questioned the c/l is the photo showing the light and the gap, it appears the rib is canted. Is it? Because that presents another issue.

It could be off, however, it was awkward holding the slide just right for the light to seep through and take a pic with the cell. 

There isn't any hang over of the rib into the ejection port, I think that is an illusion from the camera angle.

HenryA wrote:6X40 is not a standard "gun size" screw thread - 6X48 is. So really he did it "right" by gunsmithing standards. This seems to be a communication problem rather than a mechanical one. I hope it all works out well for you in the end.

It was a communication problem, AND a mechanical. I would be somewhat OK with the screws and threads as is if it wasn't for the fact it looks like it will break off since they appear to be barley hanging in there.

I'm not belittling your situation, just suggesting that it is readily fixable. He certainly could have explained about the screw choice on the front end. That would have been a much better business practice.

I'd also have investigated what the counterbores in the rib look like. You'd want screw heads that fit. That would have been part of the discussion as well. When you get new screws check that out.

I agree with Jerry.  The rib looks to be canted to the right as looking down the slide.  If that is the case then the holes will need to be filled and then re-drilled and tapped.

Tough call, but, if you draw a line parallel to the frame, the rib does not appear to be square to it.

Update:

Due to kind people, the problem has been corrected. A big thank you to Jerry Keefer who expeditiously corrected the bo-mar rib install with some substantial heavy duty screws. Also a big thank you to John Eulette  for also offering to help. Lesson learned, ALWAYS use or consult BE gunsmiths first! For reference for future bo-mar attach-ers:

After being fixed:
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Initial screw job:
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Initial screw job,

dripping with sarcasm??

The reason for the gap is to get a firm contact at the edges economically.  .  As for the screws, Brownells sells hex drive 6-48 screws.  As to the size 6 vs 8, it came from the factory with 6s.  One can assume that The factory knew what strength they needed.  Lots of these were installed with 6s and held up fine.  The screws will develop full shear strength with engagement of 5 threads, in this case about .100 engagement.  

Now, having had the opportunity to measure and inspect the original installation, a conclusion.
Part of the reason the gap existed is, the  "infallible" factory failed to machine the radius in the center, and not quite wide enough.. The mounting holes were drilled and tapped .007 off the center line of the slide. Not a lot, but a careful eye could see it. The rear most hole was also located .015 too far to the rear, also causing the rib to bind and raise when the screw was torqued against the side of the hole. Many machine workers, still use wigglers to find the edge of a work piece.. Wigglers are not exact, and it is quite easy to  be off several thousandths or more. Possibly explaining the .007 error.
The holes were corrected by using a specially ground center cutting endmill, which acts like a single point allowing the cut to be made from the true centerline zero, thereby moving the hole C/L to its proper location.. The rear hole just barely cleaned up on zero, but it did.. Each screw then has its length adjust to within .015 of the hole depth for full thread contact..  # 8 Torx Heads provide a significant gain in torque, clamping pressure, and shear strength. Another plus, by increasing  from #6 to #8 there is far less chance of breaking the fragile No.# 6 tap in a tough, harder than necessary slide.. Some old Colts are incredibly hard.

Over time the gap will present a problem. Aluminum "creeps" After a while you will notice the screws are not tight, if you do use loctite the screws will appear to be tight but in fact they are only tight in the threads but not tight on the rib. The rib will eventually move. For that reason when I make my scope mounts I use 7075 aluminum and machine it to fit to the slide without any gap.

Froneck wrote:Over time the gap will present a problem. Aluminum "creeps" After a while you will notice the screws are not tight, if you do use loctite the screws will appear to be tight but in fact they are only tight in the threads but not tight on the rib. The rib will eventually move. For that reason when I make my scope mounts I use 7075 aluminum and machine it to fit to the slide without any gap.

I believe the bo mar is steel, no aluminium anywhere.