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NM detent pics

3596 Views 22 Replies 9 Participants Last post by  Ezekiel
Does anyone have pictures of a disassembled NM rear sight with the detent modification? How deep is the spring hole? Is the position of the detent critical, furthermore, are the positions of the notches on the windage knob critical? Thinking of giving this a go on my rifle.
Mike
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· MGySgt USMC (ret)
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Almost every SAinc. receiver made in the last 20 or more years has a hole in it for this kind of NM rear sight set up. It is actually one thing that SAinc. does and no one else does (to my knowledge) direct from the factory on every receiver.

There are at least TWO common methods to make that hole and the hole varies in diameter, as well as depth, depending on the type of detent ball used.

One common method was just do drill the hole deep enough that a ball bearing was placed on the hole and went in maybe 1/3rd the depth of the thickness of the ball. These require wider notches in the windage knob.

The other method is to use an extractor detent and spring and cut the spring down so it works best. The notches in the windage knob have to be smaller for this method because you don't want the notches to allow movement around the ball/detent.

I just checked a pretty new Sainc. receiver and the hole was drilled by a Number 30 drill bit to a depth of .304" It is intended to use an extractor detent and spring.

However, this really must be drilled on a precision end mill, normally. I don't think most drill presses can do it well unless you make a drilling fixture.
 

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Or do the NM windage knob with 8 detents.

How's that going too work? if you look at the pic's that Ron posted you can see that the windage knob lugs have been removed each lug is replaced with two notches(8 total) thus giving 1/2 min changes, if you do the same with a NM knob you still have 1/2min value and no change?

For 1/4 min windage chanages your gonna need 16 notches total.
 

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The standard sight has 32 TPI whereas the NM has 64 TPI. The 64 TPI gives the NM sights the 1/2 minute windage clicks with the 4 lugs, wouldn't the 8 detents then give you the 1/4 clicks?
 

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There is another problem with 1/4 minute sights as well. While they CAN really fine tune your bullet impact, they are often confusing when you have to make a major shift when the wind changes. I know some folks who can deal with this and really like a 1/4 minute sight, but I have also known a lot of folks who after using a 1/4 minute sight - went back to a 1/2 minute sight.
 

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There is another problem with 1/4 minute sights as well. While they CAN really fine tune your bullet impact, they are often confusing when you have to make a major shift when the wind changes. I know some folks who can deal with this and really like a 1/4 minute sight, but I have also known a lot of folks who after using a 1/4 minute sight - went back to a 1/2 minute sight.
mr fisher, i saw a couple of the big team rifles a long time ago that had a notch filed on the outside face of the windage knob, where the recessed screw head was, and was colored with what appeared to be red fingernail polish. the discussion was about that very thing, for counting full revolutions in a big wind call. is this something you armorers did or was it an individual shooters perogative?
 

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Phil,

I have two of each set ups, NM with 8 detents and standard with 8 detents. The NM both on my McCoy M1s are indeed 1/4 minute clicks. The standard windage with 8 detents are on my number 1 and number 2 M1As .
 

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mr fisher, i saw a couple of the big team rifles a long time ago that had a notch filed on the outside face of the windage knob, where the recessed screw head was, and was colored with what appeared to be red fingernail polish. the discussion was about that very thing, for counting full revolutions in a big wind call. is this something you armorers did or was it an individual shooters perogative?
OMG, this brings up the story I am STILL catching a lot of good natured jibes about the last time I related it years ago on another forum. Grin.

Shooters would make marks with paint or fingernail polish on both the elevation knobs and windage knobs for a quick reference for different yard lines. We armorers kept a supply of fingernail polish for them to do it. Matter of fact, the Armorers on the BIG team had to go out and get it for them on the commercial market and that's where the story begins.

When I was new to the BIG team, and as I was walking the line to be there in case of problems, I came across a very experienced long time shooter "Giving the Sermon on the Mount" commandment that ONLY "Roses in the Snow" was the correct fingernail polish to use for marking Marine Corps Team rifles. I could not help but overhear the conversation. So at the next break, I went back to the truck and asked Ted Hollabaugh what that was all about. He almost went into hysterics laughing and then he told me.

A few years earlier, they were given some money and he and Dempsey Damron were sent to buy fingernail polish. Ted had asked his wife where to get the best deal and she said to go to a Beauty Supply Store. In those days to leave the base on official business, you had to be in uniform of the day. So Ted and Dempsey got into uniform and went to a Beauty Supply store. Now picture this, two Marines in uniform walking into such a store in the late 60's or early 70's and asking to buy a LOT of finger nail polish!!!!! Needless to say they were embarrassed as all get out.

The woman who ran the store thought someone was pulling a joke on her. It took them a while to explain to her why they needed it and she didn't fully understand, but at last they got through to her. Then she asked them what color they wanted. They said they were looking for "red." Well, the Lady explained there were probably eight dozen shades of red and what would they like to match it to? Now Ted and Dempsey both blushed and finally were able to explain it really didn't matter as long as the stuff lasted a good while before it wore off and they needed a LOT of it. The Lady finally said, "I've got one color that has not sold hardly at all and if the color is OK, I can let you have it cheap." The color was "Roses in the Snow" and it was printed on every bottle. It was a rather light red and tending almost towards but not quite a pink color. Anyway, for what they expected to buy about 60 bottles for all the shooters, they walked out of there with four GROSS of that color. By the time I joined the Big Team in 1975, they were down to only having a few bottles left. The stuff did last a good while before it wore off, so it was popular with the shooters for that reason.
 

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There is another problem with 1/4 minute sights as well. While they CAN really fine tune your bullet impact, they are often confusing when you have to make a major shift when the wind changes. I know some folks who can deal with this and really like a 1/4 minute sight, but I have also known a lot of folks who after using a 1/4 minute sight - went back to a 1/2 minute sight.
Eventually you run into the same thing with even real good fine-pitch metallic sights for smallbore and highpower bolt guns. A click doesn't move the aperture or moves it too far or the wrong direction. It's just wear & tear and the sight has to be rebuilt.
 

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Phil,

Here are three windage knobs, on the right is the NM with the 8 detents, middle is the unmodified standard and on the left is the NM unmodified .The threads do not show well, just took it with my phone.


Nez
 

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Nez, your pic's came out great, thanks. I think I will give this a go when I can find someone who can do it.

Phil,

I've had two guys machine the windage knobs for me on indexing tables, Doug Giraud, the case trimmer guy, and Gary, the owner of Phoenix Precision Match Sights. Gary is your best bet, here is his website. http://www.phoenixprec.com/index.php?main_page=contact_us&zenid=khqobt2p837avn6s23sflsqmm7

He did more than just machine the detents for me, he sleeved the base and re-cut the threads to precisely fit the windage knob thread after he re-cut the latter. The finished product has precisely cut mating threads with no slop. Good thing with Gary he has a CNC Mill dedicated for threading only.

If and when you call Gary, mention to him the prototype he did for me. He has two more rear sights from me awaitng modification right now.

If you do not want to be scared never put a dial indicator on your M1A rear sight and check the clicks back and forth.


nez
 
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