10-32 screws for a scope mount?
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  1. #1
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    Default 10-32 screws for a scope mount?

    Well has anyone ever done this? A gunsmith in training(GIT) brought in a 96 Mauser with 4 6-48 tapped holes. Screwed in a tap on each one and they were not even close to being centered or in line.
    Put the receiver in the mill and lined it up, thought of mapping the holes and drilling the blank mount with offset and angled holes to match the receiver but nixed that as too time consuming. Well let see if the holes clean up for 8-40 screws and ran a 9/64 mill in the first 2 holes. Did not come close to cleaning up.
    Looked at it real good and figured they would clean up with 10-32. He said go for it as the mount was deep enough for standard 10-32 Allen screws.

    The rifle had all the parts nicely blued and was in a custom stock the scope will cover the 10-32 screws so the over all look will not be hurt.

    The gun's owner left it with a gunsmith in San Antonio for several months with a promise to start on it right away. GIT brought it to me and while watching got something that will work in a couple of hours. Figure this was legal as the GIT has a license and was in sight of the gun the whole time.
    In another thread Thermite said we want to see photos of the 96 Mauser. Intend to post photos when the GIT emails.

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    One more question, the gunsmith asked about this bed mill. Purchased 20 + years ago with probably a couple hundred hours of use. Set up for the same job for the last 15 years and the part became obsolete more than 10 years ago. Just turned on the spindle for the first time in 10 years and it sounded OK. Turned the handles and it feels like a new machine (wonder why). The last work on the machine involved milling a .002 deep radius cut in the end of 1mm diameter tubes. Still set up for that job.
    If I remember right I paid $8000+ for the machine when new. What is a fair price?
    santecbedmill1rs.jpgsantecbedmill2rs.jpg

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    Regarding the 10-32 screws, my concern is the thickness of the receiver at the holes. You want three threads in each hole; .100" would give you that.

    A "fair" price is what you both agree on. Less than the seller wants and more than the buyer wants to pay. Start high and adjust down as the buyer adjusts up. Capitalism at work.

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    10-40 or 10-48 would be better!

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    10-40 or 10-48 would be better!

    I agree, but a search of McMaster-Carr's website did not locate either.

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    Quote Originally Posted by GGaskill View Post
    10-40 or 10-48 would be better!

    I agree, but a search of McMaster-Carr's website did not locate either.
    I did a quick glance at the Machinery's Handbook and did not find any specials till you get to 1/4. Spent more time than I wanted to get to 10-32. Making a special tap and screws would have been too much to justify. As it was the gun's owner gave us a $500.00 limit. Will call the gunsmith and remind him to send the photos. It has a nice looking stock and the oversize screw heads will be hidden. Hope it now shoots to its potential. The owner could not do anything with it before as the scope was in a severe twist with the 2 piece mounts.

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    A little out-of-the-box thinking would suggest trying M4.5x0.50 or M5.0x0.50 screws before committing to the #10 size. 0.50mm pitch is about 50.8 TPI. Would require a metric tap and screw but at least they are standard sizes.

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    When in a similar situation, I found the best solution was to obtain a new receiver and switch all the parts. The $500 ceiling makes it a reasonable option. With the courts looking to sue anything connected with firearms, I'm not sure I would want the liability of repairing a receiver. Another option might be to remove all parts, weld up the old holes, send it out for a heat treatment, drill and tap new holes and reassemble.
    Carl Gustafs Stads Mauser 1901 Modified Matching Numbers Scope - Bolt Action Rifles at GunBroker.com : 909364165

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    Quote Originally Posted by FredC View Post
    Well has anyone ever done this? A gunsmith in training(GIT) brought in a 96 Mauser with 4 6-48 tapped holes. Screwed in a tap on each one and they were not even close to being centered or in line.
    Put the receiver in the mill and lined it up, thought of mapping the holes and drilling the blank mount with offset and angled holes to match the receiver but nixed that as too time consuming. Well let see if the holes clean up for 8-40 screws and ran a 9/64 mill in the first 2 holes. Did not come close to cleaning up.
    Looked at it real good and figured they would clean up with 10-32. He said go for it as the mount was deep enough for standard 10-32 Allen screws.

    The rifle had all the parts nicely blued and was in a custom stock the scope will cover the 10-32 screws so the over all look will not be hurt.

    The gun's owner left it with a gunsmith in San Antonio for several months with a promise to start on it right away. GIT brought it to me and while watching got something that will work in a couple of hours. Figure this was legal as the GIT has a license and was in sight of the gun the whole time.
    In another thread Thermite said we want to see photos of the 96 Mauser. Intend to post photos when the GIT emails.
    First, I would not want to own a rifle that had been so badly kluged up as the repair you have described, with two botched attempts and ending with #10 screws! A horrible mess to which I also would not want my name attached.

    If no choice existed besides repairing this botched part, I would rather see the existing holes plugged with threaded plugs, permanently Loctite-ed in place, re-drilled and tapped for the correctly sized fasteners.

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    A gunsmith in training ? when my dad had his shop there were these people that would come in every now and then with the shoe box with a gun of some sort all apart and it was always there kid that did it [i often wondered what kind of people store there guns were there kids could get to them] . to a gunsmith sae threads are blacksmith threads. the only thing i can see is pass but if you own it then brownels sell gunsmith taps 10-40 or maybe a god forbid 12-40 last find a real metal gunsmith that can do the job for who ever drilled the first two sets can't

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    Quote Originally Posted by GGaskill View Post
    A little out-of-the-box thinking would suggest trying M4.5x0.50 or M5.0x0.50 screws before committing to the #10 size. 0.50mm pitch is about 50.8 TPI. Would require a metric tap and screw but at least they are standard sizes.
    Funny that you mention this M5.0X.5 thread I have a set of those taps purchased from MSC. Chinese imports that look terrible but actually made good threads. Fit a precision die bonder stamping tool (page 159 in this catalog) perfectly. Would have had to make 3 screws slot them and heat treat them. Tool room lathe was set up that day for a different job. Not sure if the HLV-H has the correct gears for that thread anyway.

    Product Catalog (Part III) - Micro-Mechanics page 159 of this link.
    Last edited by FredC; 08-31-2021 at 11:27 AM. Reason: added the link

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    Quote Originally Posted by 1yesca View Post
    to a gunsmith sae threads are blacksmith threads. the only thing i can see is pass but if you own it then brownels sell gunsmith taps 10-40 or maybe a god forbid 12-40 last find a real metal gunsmith that can do the job for who ever drilled the first two sets can't
    10-32 is a blacksmiths thread? I can look in my Machinery's Handbook and get all kinds of info on it. Limits on minor diameters, pitch diameters, sizes of the radius or flats on the crests and roots. Tell me where I can find more info than a recommended drill size for a 6-48 in Brownell's catalog. I have 2A and 3A ring gauges and plug gauges for 10-32 and it is a blacksmith's thread? Where do you get your 6-48 or 8-40 thread gauges? Or do you just make things fit the way blacksmiths used to?

    My Brownell's catalog is a 2016 and has 10-36 taps with no screws that I could find. It took about a half hour to shim and line the receiver to find out that 8-40s would not clean up. Did not like the idea of drilling new holes and making Swiss cheese out of the receiver. Waiting a week for a 10-36 tap to come in to make it a legitimate gunsmith threads would involve lining it up in the mill again as the GIT could not leave it here. Making custom 10-36 screws would have put it over budget anyway. Number 10 screws are only .026 larger than #8s. Seems like the less damage is done to the receiver by going to 10-32 than drilling another set of 6-48, not sure how plugging the bad holes would have made the receiver stronger.

    If course threads make threads blacksmith kind of work, write a letter to Mauser and ask them why they still use 1/4-22 for the trigger guards.

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    Well Thermite, a cropped and resized photo that was sent to me by the new gun smith. Photo was taken with a cellphone so the quality is not the best. This 7mm was built by the current owners brother in law. polished and reblued. stock fitting was real good in some areas and OK in others. The current owner had taken it to a SA gunsmith who did nothing to straighten out the scope mounting holes with it sitting in the shop for several months. The owner "Gravel Hauler" had the new gunsmith bring it over.

    mauserc-rs.jpg
    Last edited by FredC; 09-01-2021 at 09:00 AM.

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    Quote Originally Posted by FredC View Post
    10-32 is a blacksmiths thread? I can look in my Machinery's Handbook and get all kinds of info on it. Limits on minor diameters, pitch diameters, sizes of the radius or flats on the crests and roots. Tell me where I can find more info than a recommended drill size for a 6-48 in Brownell's catalog. I have 2A and 3A ring gauges and plug gauges for 10-32 and it is a blacksmith's thread? Where do you get your 6-48 or 8-40 thread gauges? Or do you just make things fit the way blacksmiths used to?

    My Brownell's catalog is a 2016 and has 10-36 taps with no screws that I could find. It took about a half hour to shim and line the receiver to find out that 8-40s would not clean up. Did not like the idea of drilling new holes and making Swiss cheese out of the receiver. Waiting a week for a 10-36 tap to come in to make it a legitimate gunsmith threads would involve lining it up in the mill again as the GIT could not leave it here. Making custom 10-36 screws would have put it over budget anyway. Number 10 screws are only .026 larger than #8s. Seems like the less damage is done to the receiver by going to 10-32 than drilling another set of 6-48, not sure how plugging the bad holes would have made the receiver stronger.

    If course threads make threads blacksmith kind of work, write a letter to Mauser and ask them why they still use 1/4-22 for the trigger guards.
    1/4 x 22 why lots of metal and when you have some kid that came off a farm installing a screw and the only thing he ever screwed before was his sister paul did not want him cross treading it and it a lot harder to do that with the 22 tpi but now that the gloves are off why don't you just fess up and come clean and tell us your the one that drilled all the holes in this gun and why your at it put some Phillips head screws in there as you a class act . my dad use to say that he was not a gunsmith as he had seen to meany guns screwed up by so called gunsmiths and that he was a machinist so with that in mind ya maybe you are a gunsmith

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    Let's refrain from any more personal attacks.

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    In 2011 I drilled and tapped 10-32 screws into a Mosin Nagant to mount a scope base. I worked on the calculations of how much torque. There was only 3 threads of engagement.

    cutting-off-10-32-cap-screws-ati-mount-m44-mosin-nagant-receiver-2-12-2014.jpg

    This website was a big help in calculating the torque, especially the guy from Caterpillar.

    Tapped thread depth/strength question

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    ClarkMag, interesting thread.
    Saw the comments by Stan Dornfeld. He called me a couple of years ago and could not figure out how to get back on the forum. By then he had dementia pretty bad. He still had many of those vices he made in his avator, but could not figure out how to sell one to a forum member that wanted one, getting old is tough but it beats dying young.
    Last edited by FredC; 09-22-2021 at 03:54 PM. Reason: spelling

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    Years ago I was picking up a pair of Mauser actions at a local gun shop. There was a younger guy there that was a gunsmith in training, and he asked me for advise. He was having a problem with a customers Remington 700. The top edge of the nose of the bolt was rubbing against the receiver as the bolt was being closed and because of this interference the rifle was shooting inaccurately. The kid wanted to know how to modify the receiver to solve this problem. I gave him this advise, which is the same advice I give to all young gunsmiths: The bolt is a part. The trigger is a part. The barrel is a part. But the receiver is THE gun. If you screw up a part you can replace it. If you screw up the receiver you've just opened up a complicated can of worms. Do the repairs on the part, not the receiver. In the instance of the OP's problem - machine a scope mount with the holes offset to match the hole pattern on the receiver. For several reasons, this is the best course of action that you should take on this problem. Either weld up the holes in the existing scope rail & re-drill, machine a new scope rail from a blank piece of Picitinny rail, or do whatever it takes to make or modify a scope mount to fit the receiver, but DON'T enlarge and tap the holes in the receiver. If the firearm owner shoots an overcharge round and the receiver ring splits because it has an oversized hole in it, that's bad. If the larger screws reach down far enough to contact the bolt, that's bad. If the larger thread pitch causes the scope mount screws to shoot loose, that's bad. Do the job right, make the part fit the receiver.

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