Before attempting this procedure, take two very important
- Ensure that your HK4 is unloaded.
- Select a workspace in which you will not lose any of
the springs and pins that invariably fall and roll towards
the nearest abyss.
Begin with the slide assembly sans barrel or mainspring.
- Pivot the extractor slightly outwards to expose the hole
that runs through it.
- Insert an unfolded paperclip through this hole so that
the extractor will remain in this position.
- Insert a long, flatheaded screwdriver through the muzzle
end of the slide and remove the cylinder head screw which
retains the breechface plate.
- Remove the breechface plate
- Rotate the safety lever to a position halfway between
"Safe" and "Fire".
- Remove the firing pin and firing pin spring from the front
of the breech. (This may require the gentle application of
some needlenose pliars.)
- Wiggle the selector lever out of the slide.
- Remove the paperclip that is holding the extractor outwards,
and wiggle the extractor out of the slide. ("Wiggle" does not
have a technical connotation, but you certainly do a lot of it
during this entire procedure.) Tension on the extractor is provided
by two set bolts with a spring between them, and this tension
should slacken once the selector lever is removed. All three
of these parts should fall out of the front or rear of the slide
once the selector lever and extractor are removed.
If there was ever a time to clean all of your HK4's slide
components, it is now.
Do not reassemble in the reverse order. Instead:
- Choose the proper extractor for installation. (One
HK4 schematic that I have seen references 8 different
extractors - 4 old style and 4 new style for each caliber
- yet did not reference the universal extractor, so there
may be as many as 9 extractors to choose from. Good
- Insert the selector lever into the slide.
- Reinsert both of the set bolts along with their
compression spring through the hole in the front of the
slide that is immediately behind the extractor port. The
set bolts are interchangeable, but be sure that:
The compression spring and the firing pin spring are not
interchangeable, so be sure to put the correct spring between
the set bolts. The compression spring is shorter and stronger
than the firing pin spring.
- the tapered end of the rear set bolt faces rearward
to make contact with the selector lever, and
- the tapered end of the front set bolt faces forward
to make contact with the extractor once it is installed.
- Press the extractor into place by using its retaining
stud to force the set bolt rearwards.
- Again, pivot the extractor slightly outwards to
expose the hole that runs through it, and reinsert your
handy paperclip to hold the extractor in this position,
thereby allowing sufficient room to reinstall the firing
pin and breechface plate.
- Insert the firing pin through the breech with its rear,
chisled tip facing downwards. The square stud on the
firing pin points upwards, and properly seating the firing
pin may require some patient maneuvering.
- Slide the firing pin spring over the tip of the firing pin.
- Press the breechface plate into position with the
appropriate side facing forwards. (If you are performing
a .22 conversion, then the "R" - for rimfire - stamp should
face forward. If you are performing a .25, .32 or .380 conversion,
then the "Z" - for centerfire - stamp should face forward.
Also, be sure to insert the tip of the firing pin through the
proper hole in the breechface plate: the bottom hole is used
for centerfire conversions, the center hole is used for rimfire
conversions and the top hole is reserved for the cylinder
- Insert and tighten the cylinder head screw.
- Remove the paper clip from the extractor.
- Reassemble the pistol.