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  1. #1

    Default FM/23 peep sight aperture question

    I have an FM/23 with a Lyman 48(M) sight. It's missing the peep aperture. Is there a "common" size (diameter and peep hole diameter) aperture for this sight on this rifle? Anyone know where I can find one? Thanks.

  2. #2
    swede's Avatar
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    That should be a common part to find in the USA . Many aperture sizes & outside diameters to choose from . Gun parts dealers at a local gun show should be able to help you out . Search Lyman 48m on EBAY & see if you can find them . I doubt there is only one specific size for the fm23 . That would be an option for the shooter .

    The 48M on my fm23/36 has a 2.5m/m ( .098" ) aperture .

    I have a 48M with a Crown marking & a 1.2m/m ( .047" ) aperture .

  3. #3

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    Quote Originally Posted by swede View Post
    That should be a common part to find in the USA . Many aperture sizes & outside diameters to choose from . Gun parts dealers at a local gun show should be able to help you out . Search Lyman 48m on EBAY & see if you can find them . I doubt there is only one specific size for the fm23 . That would be an option for the shooter .

    The 48M on my fm23/36 has a 2.5m/m ( .098" ) aperture .

    I have a 48M with a Crown marking & a 1.2m/m ( .047" ) aperture .
    Thanks Swede. I've been checking the local shows and no one seems to have the metric threaded apertures. I'll keep an eye on Ebay...maybe someone will pop up with one that has metric threads.

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    Dave, why not asking Lyman direct? Lyman Products Your Primary Source for Reloading Equipment
    Contact their customer service with your problem.

  5. #5
    swede's Avatar
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    Much to my surprise , the Lyman aperture threads are metric , M6 x .75m/m pitch . Never thought to check them before now , as I assumed they were American threads . The Fäldt diopter uses the same thread , but they are to short for a Lyman sight . The Lyman aperture has a long neck to clear the base of the windage wing of the sight .

  6. #6
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    Guys:

    For custom apertures and adapters, contact my buddy Joe at:

    aperturesnmore.com

    Contact him with your specific needs, not everything he does is on his site.

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    Default fm/23 rear peep sight

    Good Day,
    The rear peep for the fm/23 or fm23/36 is a tough bird to find but it can be done. I did find an extra one when mine turned up missing but it took quite awhile.

    Michael
    Attached Thumbnails Attached Thumbnails DSC04913.jpg   100_0417.jpg   100_0416.jpg   DSC04918.jpg  

  8. #8

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    Thanks for the advice guys! Joe at spertureandmore has a CZ aperture that should work....I'll be keeping my eyes peeled for an original aperture.

    Beautiful fm/23 Michael!

    I wonder how many of the original 501 have shown up????

    David

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    Remember that the Crown marked aperture belongs to fm/23-36 and not to the fm/23.
    Regards,
    ARILAR
    Arms are for hugging

  10. #10

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    OK...I'm back at it again. Unfortunately, the peep has a very strange thread. I contacted Lyman (shoulda done that first, Box ;-) ) and their response...

    "Our sights disks have always used the same thread (.225" x 40), so our
    current sight disks should fit. Here is a link to our website listing them; htt
    p://www.lymanproducts.com/store/page189.html "

    So, I've ordered a peep from them. A 1/4" thread was too big and a #10 was too small. I suppose this was why I thought it was metric...A 6mm thread wouldn't start and a 5mm thread went straight through....so this really made it odd. I can't say that a .225" X 40 thread pitch is a common thread.

    I found an interesting link here that discusses a related issue...and sheds more light on this thread size...
    http://www.assra.com/cgi-bin/yabb/Ya...num=1142218654

    David

  11. #11
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    Well , that is good information !!!!!!!!!! That is an odd thread size for sure . Similar to Mauser , they used the British Whitworth thread system , but used different pitches , such as 1/4"-22 instead of the standard 1/4"-20 thread on the trigger guard screws . I guess they made the gun owners come to them for their threaded parts .

  12. #12

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    Sorry to drag this up again, but it seems that the Lyman 48M has a very unique aperture thread! After trying the CZ aperture, every standard and metric thread around this size, AND the Lyman aperture, it seems nothing fits my fm/23! My sight has a 1911 date on the side of it...maybe Lyman changed their threads sometime after that date.

    I was wondering if anyone out there has the capability of measuring the threads on their 48M? An optical comparator, or a measuring microscope, can be used to measure the thread pitch and a micrometer for the thread diameter.

    Thanks.
    David

  13. #13
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    So , you got a Lyman factory threaded aperture ? It did not fit ? Look carefully & see if your diopter threads are buggered up , cross threaded or retapped to another size .

    I got out my " Lyman 48 M J " which is " crown marked " . The aperture thread measures .234" , on the outside , which is only .002" under 6m/m ( .236" ) . So , that is .009" bigger than the .225" x 40 thread that Lyman sent you . I have a Brownells Metric Thread Checker Plate & it has two 6m/m threads , a 1.0m/m pitch and a .75m/m pitch . My aperture fits the .75m/m thread on the Brownells plate perfectly . That is what I originally said in post #5 of this thread , and I now believe that is a fact , at least on mine . Unfortunately , I do not have any spare apertures .
    Last edited by swede; 08-20-2012 at 04:45 AM.

  14. #14

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    Thanks Swede. I'll double check the threads on the sight to make certain they aren't botched up. I appreciate you checking your sight for me.

    David

  15. #15
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    UPDATE : I just checked the Lyman sight on my fm23/36 and it has the correct .225" x 40 thread . The aperture from this sight will screw into my other Lyman sight with the M6x.75 thread , however it is very loose . I have a M6x.75 thread die and I can thread a piece of 1/4" steel rod for you to check & see it that is the thread you have . If interested , send me a PM with your name & address .

  16. #16

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    Thanks Swede...sent a PM.

  17. #17

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    FINALLY found a 7/32-40 tap to chase the thread in the Lyman sight and that fixed the problem. I could find only starting taps so I cut one down to make a plug tap and it's all good now. Thanks for all the advice guys.... I really appreciate it. Now I have an FM23 I can actually aim.
    David

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    Quote Originally Posted by FlightRN View Post
    Good Day,
    The rear peep for the fm/23 or fm23/36 is a tough bird to find but it can be done. I did find an extra one when mine turned up missing but it took quite awhile.

    Michael
    Michael, what a nice quartet you have there!! Still on the hunt for my fm/23!! Ken Buch had one before my move to Texas, but I just couldn't pull the trigger. Can you believe that!? It won't happen again.
    "Shoot straight you bastards! Don't make a mess of it!"

    Lt. Harry "Breaker" Morant, February 27, 1902, Pretoria, South Africa.

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