How to straighten a front site block.
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Thread: How to straighten a front site block.

  1. #1
    Gunco Regular Thumb Clip Pull Pin's Avatar
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    Default How to straighten a front site block.

    Do not take a hammer and smack it! You will bend the heck out of the upright portion of the site. Apparently they are made of a pretty soft cast metal!

    You will need to put some lay out dye or paint on the barrel and the front site block and scratch a couple of witness marks on these.

    (Note- This picture was taken after I moved the front site block counter clockwise a tiny bit and then pressed the assembly back onto the barrel.)

    You will need to remove the two pins that are pressed in through the front site block/barrel assembly. I use a small punch, a ball peen hammer, and a nylon bench block. Get some one to help you hold the rest of the rifle still while you are driving the pins out.

    Next you will need to press the front sight block off. I made a set of ?Xebec style? blocks out of aluminum. I bolt them around the barrel, just under the site. Then I use a short piece of brass to protect the muzzle. I used the 20 ton press to press the barrel out of the front site block.

    Next you will need to move the blocks down to the gas block assembly and bolt them in place. I also paint on a little bit of ?Never Seize? to that part of the barrel where the front site goes.

    Next you will have to align the front and rear sights so that both are at ?top dead center?. I used a line level on the front site and a torpedo level on the rear site.

    Now for the hard part! You have to hold everything together and put the complete assembly into the press. Make sure that the barrel and the front site block are exactly lined up with the long axis of the press. Press the front site back on slowly. Stop if the site block begins to bind or kick out. Stop if the barrel gets out of line with the axis of the press. Use brass or steel shims to get the long axis of the barrel back into line with the long axis of the press.

    Look through the holes for the front site block pins now that you have the front site block full pressed back on. Notice that the metal of the front site block and the metal of the barrel are no longer in line. You will also find that your old pins will not fit back into the old holes.

    I took a break at this point. I reassembled the rifle. I took it down to the range and shot five rounds at a fifty yard target to see if I had the sites aligned properly. I had a three shot clover leaf at twelve o?clock, ten inches high. Two other shots were called high and right. I rechecked my witness marks. The front site had not moved during this test!

    I measured the factory pins when I returned home. They measured 0.120?. I found that a 3mm drill fit into the front sight block pin holes. Three millimeter equals 0.11811?. This means that there was about a two thousandths press fit between the pins and the pin holes.

    The old holes need to be opened up to a larger size so that the front site block metal and the barrel metal all lines up again. I found that a number thirty one drill measures 0.120?. I used this to open the front site block pin holes up. I just adjusted my drill press to the slowest speed (660 RPM). I used plenty of cutting oil and went slow.

    I did make an alignment fixture so that I could drill the holes straight, but I found that I did not need it. The drill cut smoothly, and did not bind.

    The next step is making some replacement pins. I found out the hard way not to use common nails as raw materials! I took pictures of the process of pin making, just substitute oil hardening drill rod where I used a common nail for raw material.

    I used an old light duty Black and Decker ?? drill motor mounted in a bench vise and a double cut mill bastard file to turn the raw material to 0.124?.

    Then I used 220 grit aluminum oxide sandpaper to polish the pin smooth and to reduce the pin diameter to 0.122?.

    Now it is time to harden the part! Remove the part from the drill. Hold it with a set of vise grip pliers. Heat the steel with a torch until the steel looses magnetic attraction. Hold the steel at this temperature for thirty seconds or so then plunge the steel into oil. (I used thirty weight motor oil.) Next, put the part back in the drill; polish it lightly with steel wool or 220 grit sand paper. You are removing the black, burned oil from the surface. You are not removing metal here! You can reheat the steel until it turns ?straw? colored to temper the part. I did not do this additional step.

    Next, measure the length of the original pin. I used a black ?Sharpie? marker and a set of calipers to lay out the length on the pin while it was spinning in the drill motor.

    Next, use the Dremel tool and a cut off wheel to cut the pin. ?Leave the mark? so that you can adjust the over all length. Do not cut all of the way through as the new pin my go flying off and get lost. (Ask me how I know!) Use a pair of pliers to snap the pin off. It is going to be pretty hot!

    To be continued...

    Yours,
    Thumb Clip Pull Pin.
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  2. #2
    Gunco Regular Thumb Clip Pull Pin's Avatar
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    Default Straightening the front site part 2.

    Dress the ends of the pin with files and sand paper. The steel will be pretty hard and the files may not cut it. Don?t force the file to cut! Use a sharpening stone or a bench grinder to dress the raw end.

    Next, I applied a little bit of ?Never Seize? on the new pin. I used a three inch ?c? clamp and one half of my aluminum gas block fixture to press the new pin into the new front sight block hole. I did not want to use a ball peen hammer to pound it in because I did not want to disturb the front site.

    Repeat this process for the second pin hole in the front site block.

    Here is the reason that you do not want to use not heat treated common nails as raw material for pins!

    Yours,
    Thumb Clip Pull Pin.
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