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

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

Post by scrum derringer on Mon Feb 01, 2016 10:33 am

First topic message reminder :

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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Last edited by scrum derringer on Mon Feb 08, 2016 10:32 am; edited 1 time in total

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

Post by Jerry Keefer on Fri Feb 12, 2016 11:07 am

I have made countless scope bases machined on the receivers such as these.. I can't do enough of them to meet the demand.. Years worth.. From Police Swat Teams to hunters and some target shooters from 6061 and not  one has ever failed..NOT ONE..




Last edited by Jerry Keefer on Fri Feb 12, 2016 11:26 am; edited 1 time in total

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

Post by s1120 on Fri Feb 12, 2016 11:09 am

Jerry Keefer wrote:
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.

And this is the reply from a smith who knows what hes doing!!  Glad to hear its all up and running correctly!!  nice to know there are people out there that know their stuff!

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

Post by Froneck on Sun Feb 14, 2016 4:45 am

Ooooops, been so long sine I fooled with Bomar ribs I forgot they were all steel!
 Yet I prefer 7075 when making scope bases. It is the strongest 130 brinell, 56,000psi yield and most expensive. Followed by 2024 120 Brinell, 47,000psi yield, and is about 20% less cost than 7075. 6061 is on the bottom with 80 Brinell and 35,000psi yield and is about 82% cheaper than 7075. However it can be welded.

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

Post by Jerry Keefer on Sun Feb 14, 2016 6:40 am

Froneck wrote: 6061 is on the bottom with 80 Brinell and 35,000psi yield and is about 82% cheaper than 7075. However it can be welded.

That's one reason I use it.. If one of those  bases by chance should break,  I can weld it up and recycle it back into service.
I have some Krytonite on order, but it has been placed on back order.. I also have a hook at Cabot.. They are now using meteorites, and I hope to get a chunk to try soon..
Incidentally, there is a sub forum on Face Book, called Firearms Machinist... many of those guys are at the very top of the heap..nice place to share your photos.. Give them try...SmileSmileSmile

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

Post by james r chapman on Sun Feb 14, 2016 6:56 am

What firearm requires a 56k yield? Why would anyone pay 82% more for something that extravagant.

I want mounts for a 1911 or target rifle not a Saturn V!

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

Post by Froneck on Sun Feb 14, 2016 7:53 am

A one inch Square of 7075 at Mcmaster Carr is about $35, that's extravagant? 6061 is about $7. Put on a target pistol to hold a scope that's at least $100 for a cheap one and up to $600ish for the top of the line I'd want the best. However it's way off topic but I will end with,, if I broke a scope mount I wouldn't want it welded back together.

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

Post by Wes Lorenz on Sun Feb 14, 2016 8:16 am

Jerry Keefer wrote:
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.6061 is on the bottom with 80 Brinell and 35,000psi yield and is about 82% cheaper than 7075. However it can be welded.

That's one reason I use it.. If one of those  bases by chance should break,  I can weld it up and recycle it back into service.
I have some Krytonite on order, but it has been placed on back order.. I also have a hook at Cabot.. They are now using meteorites, and I hope to get a chunk to try soon..
Incidentally, there is a sub forum on Face Book, called Firearms Machinist... many of those guys are at the very top of the heap..nice place to share your photos.. Give them try...SmileSmileSmile
Jerry,
Krytonite.........I'm jealous. You know some of that creepy aluminum just flew 4.5 billion miles to Pluto, so by now that satellite must be shake, rattle, and rolling.

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

Post by Froneck on Sun Feb 14, 2016 8:41 am

Oooops forgot to mention the length, that 1" X 1" X 12" and it gets cheaper in longer lengths 6061 is $29/6 feet and 7075 is $143/6 feet. Plus that's at McMaster Carr, prices are less at local metal supply company.
 Temperature is space is Absolute 0 no expansion problems like at Perry in the hot sun the gun can get almost too hot to touch and the next day its cold! No stress in floating around in space, the crane on the shuttle couldn't lift it's own weight, lot different than holding a scope on a slide mount. Besides 7075 is used quite a bit in Aerospace and it gets near the strength of steel yet remains light weight. But As I said before this is way off topic, I will use only 7075 for my scope mounts. Nuff said!

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

Post by james r chapman on Sun Feb 14, 2016 9:12 am

Well, I suspect we're about as far off topic now as that satellite is. Lol

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

Post by Colt711 on Sun Feb 14, 2016 4:54 pm

Jerry,
I really enjoy seeing your work illustrated. Nice photography too.

Ron Habegger

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

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