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    My Gun Projects

    Here is a quick pictorial on how I modify an mg42 bolt to semi configuration.

    I start by turning a 1.5" steel bar to 1.280" diameter
    for a distance of 2.6" and drill a 13/16" hole 2.5" deep

    Next I use a long boring bar to finish the inside diameter to .940

    Then its time to cut the angle on the inside edge that
    matches the projection on the rear of the stock carrier.
    I have found its easiest to just
    set the compound slide to just under 6 degrees and
    use the boring bar, checking the fit
    after every pass. You will also need to turn the outside
    diam of the first .10" to a diameter of 1.280 to
    fit inside the spring ret ears on the original

    After using the parting tool to cut the bolt extension off
    at a length of 2.5" its time to turn it around in
    the chuck and cut the spring seat.
    I use the same boring tool and make the seat .12" deep
    and aprox .010 in diam larger than the spring.

    Now its time to insure the spring seats snugly and
    debur any sharp edges.

    Next place the turned bolt extension on a set of
    parralels in the vice on the milling machine and cut a
    shallow flat. This will allow me to machine
    the flat on the other side and remove the part from
    the vice to check the fit and return to the vise in
    the same position.

    With the small flat down I then machine a
    flat on what will be the top of the
    extension and mill down a proper distance so the extension
    is at the same level as the top of
    the carrier.

    The next step is to machining the other side
    of the extension down so its at the same
    level as the flat on the bottom of the carrier where the
    roller stud hole is.

    Here are a few bolt extensions nearly done.

    The last step is to machine a slot for clearance
    of the rotating hammer.

    Here are a few bolt extensions ready to be welded in place.
    Next I will detail the welding jig which consist of an arbour
    that fills the center of the carrier and runs
    the length of the assembly keeping everything aligned ,
    a plug that fills the bolt extension and a large collar
    that fits over the bolt extension to act
    as a heat sink and a retraint to insure the extension doesnt
    distort from the heat of welding

If you would like to order one of these bolt extensions or have your 42 bolt converted to semi configuration click this link to send me an email.

The next steps are to remove the roller
that actuates the feed mechanism and to mill the pad down
on the bottom of the carrier were the original sear and charging
handle engagement notch are located. The roller is fairly
easy to remove, I just use the dremel tool to grind down the peened
end of the roller and push it out. I then use a 3/8" carbide
endmill to machine the pad down to within .010 of the surface
of the bottom of the carrier, I then cut a 1/2" wide slot
across the width of the carrier with its front edge at the same
location as the original charging handle notch. The notch needs
to be machined to a depth were it just breaks thru the inside
of the carrier. This will generaly leave a carrier thickness
of .12" at the pad.

This pic shows the slot for the new angle
shaped piec that will be welded in place for the charging
handle to engage as can be seen on the completed bolt assembly
in the pic

At the bottom of this pic you can see the jig
I use to align the carrier and extension for welding.
At the right is the collar that keeps the extension from
distorting during welding, its split lengthwise and clamps tightly
around the extension.

Mandrel in.

Heat sink in place.

New roller pin bieng machined.

Original roller on the left, new roller pin
with needle roller bearing in the center, and new pin on the right.

If you would like to order one of these new feed roller assemblies or have your 42 bolt converted to semi configuration click this link to send me an email.




Here is the delrin bushing I press into the ejector tube to help support the rear of the firing pin.

Here are a few pics of the firing pin bieng machined from O-1 tool steel. I am machining these to the same profile used by BRP to make finding a replacement pin down the road fairly easy.

This is the roller key bieng drilled for the firing pin to pass thru.
Its case hardened to a depth of about .03, I usualy just take a 2 flute carbide
endmill and plunge thru the key making sure I am lined up with the original fp
pocket on the other end.

Basic layout of all the components.

New roller pin bieng alligned and pressed into the carrier.

Firing pin inserted thru new roller pin to insure alignment.

Everything layed out for insertion into carrier

Final assembly.

If you would like to have your 42 bolt converted to semi configuration click this link to send me an email.

© 2005 Thompson Machine  Sunny  Florida;  USA