Milling and mounting for a red dot

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  • ditcherman

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    Suppose someone wanted to direct mount a red dot on a pistol slide, and tolerances being what they are, and milling skills being basic beginner, and mill not a modern CNC but an old Bridgeport….

    Would you try to mill so the slide is in contact with the front side of the optic, or the rear?

    Another way to ask this is firing and slide movement rearwards more powerful and shocking to the mount bolts than forward movement by the spring?

    I’m guessing the firing process is more of a shock but would love some opinions.

    What say ye INGO?

    The only examples I have really aren’t bossed on either end, just held on by the screws, which has surprised me.
     

    nucular

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    Maybe only somewhat related but when you mount an optic to a rifle rail, you press it forward before you tighten it down. I would assume the same principle applies to pistols so you would want the front of the optic pressed up against the slide.
     

    ditcherman

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    Maybe only somewhat related but when you mount an optic to a rifle rail, you press it forward before you tighten it down. I would assume the same principle applies to pistols so you would want the front of the optic pressed up against the slide.
    Thank you, I assumed the logic might be the same as well, but with the optic moving, fixed on the slide was just curious if anything might be different.
     

    tcecil88

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    I will have to double check the one that AllenM milled for me but I think the cut had a very close tolerance to the length of the optic. I don't recall any gap on either side.
    This is why I switched from the Glock MOS plates to a Forward Controls Group plate on my Glock 40 10mm. The plate was a tight fit to the slide and the optic was a tight fit to the plate front and back. More support for the optic and no shifting under recoil. To me, the tighter the tolerance on both ends of the optic, the better. The optic takes abuse 3 times during the firing cycle. 1) The shock of initial firing where the slide tries to move out from under the optic. 2) The shock of when the slide stops to the rear and then goes back forward and the optic is still trying to catch up and 3) when the slide stops forward after chambering the fresh round and the optic is still trying to go forward.
    The OEM MOS plate was a sloppy fit wit no front or rear support for the optic.
     

    ditcherman

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    I will have to double check the one that AllenM milled for me but I think the cut had a very close tolerance to the length of the optic. I don't recall any gap on either side.
    Allen cut a Romeo1 Pro into a CZ 75 slide for me; the way it was mounted it sat with a gap on both ends, but on closer examination it can be mounted so it bosses on the rear. It can’t tighten up and touch the front.
    It’s a possibility that he mounted it touching the rear and I moved it but I don’t think so.
    Only maybe 300 rounds through it, but I know those rounds were with a small gap at both ends and the sight didn’t move, so that’s good.
     

    AllenM

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    Even without CNC you should be able to fit it fairly close on both ends.
    The main thing is using a sharp enough end mill that it doesn't leave a radius at the bottom corners of the cut so that to optic can't sit flat.
    Once cut be sure to visually make certain there is no gap under the optic before screwing it down.

    The bosses are nice a press fit is nice but the screws do hold well.....
     

    Slow Hand

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    Here is an interesting article with some good data.

    Slide acceleration article


    1718231601346508418.jpg


    In the above graphic, A is initial slide movement upon firing. B is the slide hitting the slide stop. C & D are the slide hitting. The breech face (kind of like bolt bounce). It was assumed that F was the slide slowing to pick up a new round. So, it looks like the biggest shock is the slide moving rearward, but the slide stopping is a close second, which is in the opposite direction.
     

    ditcherman

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    Even without CNC you should be able to fit it fairly close on both ends.
    The main thing is using a sharp enough end mill that it doesn't leave a radius at the bottom corners of the cut so that to optic can't sit flat.
    Once cut be sure to visually make certain there is no gap under the optic before screwing it down.

    The bosses are nice a press fit is nice but the screws do hold well.....
    Thanks!
    I cut a blank out of some scrap, as much to practice my math as anything and it turned out ok. Cut the front radius with a fly cutter, which seems crazy but it’s what I had, and that’s the corner I’ll be concerned about.
    It’s a press fit for a Romeo, but loose up front for a Eotech EFLX, but not by much.
    I’ll do more checking on the bottom though.
     

    ditcherman

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    Here is an interesting article with some good data.

    Slide acceleration article


    1718231601346508418.jpg


    In the above graphic, A is initial slide movement upon firing. B is the slide hitting the slide stop. C & D are the slide hitting. The breech face (kind of like bolt bounce). It was assumed that F was the slide slowing to pick up a new round. So, it looks like the biggest shock is the slide moving rearward, but the slide stopping is a close second, which is in the opposite direction.
    That is some great info.
     

    Steelwaver

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    Maybe not directly related, but you press an optic forward before tightening it down when mounting it to a rifle rail. I believe you would want the front of the optic placed up against the slide on a pistol.
     

    AllenM

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    Thanks!
    I cut a blank out of some scrap, as much to practice my math as anything and it turned out ok. Cut the front radius with a fly cutter, which seems crazy but it’s what I had, and that’s the corner I’ll be concerned about.
    It’s a press fit for a Romeo, but loose up front for a Eotech EFLX, but not by much.
    I’ll do more checking on the bottom though.
    Necessity is a mother :)
     

    Lpherr

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    Wish you were closer, you’d use it to its full potential. I’ve had it a while and just learning.
    Done some basic farm work with it, enough to pay for itself.

    Also, I’m sure the new CNC machines are where it’s at.
    CNC is only as good as the programmer, and how well the machine is set up.
    If the machine has any slop, it can ruin a project with tight tolerances. If cutter dia.
    isn't exact, it to can ruin the project with those tight tolerances, or at minimum if it's
    undersized, is cause a program adjustment. CNC is great for production runs, once dialed in, but for a one off, I would choose manual.
    With manual machining, the tolerances can be adjusted on the fly, without having to change the toolpaths.
    I'm guessing it's just a square dado being cut in the slide? I'm sure you can do it.

    Maybe AllenM's opinion would be different.
     

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