Apex Gunsmithing
2Feb/16

Detail Strip Guide: HK300 (PREVIEW!)

This is a preview draft of a guide I wrote a couple of months ago but decided needed more detail.  With the new camera in hand and a video format in the works for video guides as well, I'll be working on a LOT more guides in the coming months!

 

Once upon a time, Heckler & Koch tried their hand at making more traditional wood and steel "sporting" arms.  For a brief period in the 70's and 80's, they brought out a series of premium priced firearms that sold decently, but ultimately not well enough to continue the trend.  It's strange to think of the company responsible for the USP, MP5 and so many "tactical" firearms once had a catalog that had more in common with the Sears sporting goods section than a SWAT team armory, but the sporting phase was one of a few attempts the company made to find their niche when military contracts began to drop off.  If it weren't for that pesky money problem, the 70's and 80's may very well have been a golden age of H&K; two decades of crazy risk taking, innovation in design and new materials finally wound down into a brief dance with disaster before the USP helped save the company.

Born from this tarnished golden age was the HK300, one of the few semi-automatic, detachable magazine fed .22 magnum rifles you can get your hands on.  It's difficult to find information on just how many of these rifles were made, but the numbers I've found point to less than 30,000 with an unknown number of those imported into the US.

To my knowledge, this is the ONLY detail strip guide for the HK300 rifle on the internet.  I hope it helps someone!

It's not a pristine example, but good luck finding one under $1500!

It's not a pristine example, but good luck finding one under $1000!

Disassembly

1. Remove the trigger pack.  Trip the small latch behind the trigger and voila, the modular trigger pack pops right out.  H&K were among the first companies to utilize polymers effectively for guns, beyond just handguards or stocks.

Modular!

Modular!

Standard sizes and shouldn't be tight.

Standard sizes and shouldn't be tight.

2. Remove the stock bolts and magazine well shroud.  The barreled receiver will lift out, and a rectangular polymer spacer resides in the stock.

Note the direction of the polymer stock insert for later.

Note the direction of the polymer stock insert for later.

3. Remove the charging handle.  Unscrew the two small flathead screws and lift off the retaining bar.  Note the one sloped side for later, since it only assembles one way.  The charging handle itself lifts off, and doesn't require any further disassembly unless you really want to.

Sloped face of the bar faces down when assembling later.

Sloped face of the bar faces down when assembling later.

4. Remove the bolt assembly.  Pop off the receiver endcap by rotating it either direction.  Underneath, a retainer with a rubber buffer is held into the receiver by a large pin.  Push that out, it isn't a tight fit.  Now you can pull out the retainer and slide the bolt assembly out the back.

The receiver cap can be fiddly but should pop off.

The receiver cap can be fiddly but should pop off.

5. Strip the bolt.  I didn't take a picture of this for some reason, but the extractor is the flat spring steel piece on the bottom of the bolt which is retained by small semi-circular protrusions.  The firing pin and spring can be removed by driving out the pin visible in the above image.  Very straightforward, it's just a big chunk of steel!

6. Disassemble the magazine well components.  In order to avoid scratching up the gun I opted not to do this a second time to take pictures, so be careful!  The magazine catch spring is a long, strangely shaped contraption that wraps around it.  Lift the legs on the left side (pictured) off of the magazine catch and you can remove the spring.  That accomplished, you can pop the magazine catch itself off easily and turn your attention to the magwell.  The large spring retaining the magazine well has an open end in the front, so collapsing the legs inward and lots of wiggling will eventually free it.  Overall this portion is not especially necessary, but I wanted to cover it since it's not as straightforward as other steps.

Tricky little bugger.

Tricky little bugger.

7. Disassemble the trigger group.  This is where it gets fun, and I wasn't able to take step by step images due to the lighting and small parts.  The HK300 uses a very clever recoil spring system powered by four tension-adjustable springs which are linked to a pair of lever arms.  Also note the safety doesn't simply deactivate the trigger, but lifts the hammer off of the sear.

  1. Let the hammer down and push out the pin directly above the trigger.  It will push out easily, and acts as both a trigger pivot and pivot for the recoil spring arms.
  2. The two pins in the center are the hammer pin and hammer plates pin, the former being the center-most and larger in diameter.  I'm not sure order matters, but I drove out the smaller pin first, then the hammer pivot pin.  The hammer assembly will come out, but be aware of the dual hammer springs under it.
  3. With these two pins removed, the recoil spring assembly will lift out with some wiggling.  The assembly consists of an endplate, four recoil springs with screw-adjustable rods, an internal cross pin limiter and the two recoil lever arms.
  4. Now that it's mostly gutted, you can remove the hammer springs and rods, drive out the final pin at the bottom front and remove the sear and its spring underneath.  Again, the sear pin acts as a pivot and has two holes for the hammer spring guide rods.
  5. The trigger will lift out easily, but be wary of the small spring and plunger rod that acts as the return spring!
  6. The safety can be removed by rotating it and pushing it out right to left, be wary of the spring powering it.
  7. If you really want to, you can drive out the tiny pin that retains the latch behind the trigger and take it apart as well.
Order of operations is the key.

Pins left to right: Sear pin, hammer plate pin, hammer pivot pin, trigger and recoil lever arm pin.

This one is a doozy.

This one is a doozy.

From top to bottom:

  • Trigger guard housing
  • Recoil assembly (4x springs and rods, 2x arm levers, 1x endplate, 1x limiter pin)
  • Hammer springs and rods
  • Hammer assembly (2x plates, hammer, hammer spring guide rod pin with holes)
  • Sear bar, trigger and sear lever (attached to trigger with a wire spring)

Reassembly Tips

The biggest issue with reassembly is making sure the alignment of the rods and pins with through-holes is correct.  You only have to fight the hammer springs briefly, and they're not too bad at least.  Use the image above as a reference for how the plates pinned to the hammer should be lined up, since you can try to assemble them upside down and it won't work.

When reassembling the bolt into the receiver, the retainer and buffer need to be oriented correctly or the gun won't work.  The retainer and buffer should be aligned so the open side is down and the flat cut on the retainer faces the top of the receiver.

Final Thoughts

The HK300 is a cool, somewhat rare piece that happens to be one of my favorite oddities - a semi-auto .22 magnum.  The design is among the most fascinating I've seen in a rimfire, and really shows the outside the box thinking going on at H&K during their era of spitballing designs.  It's a real shame they weren't more financially successful at the time and have become collector's pieces today.  Though it will be a while before I can test it myself on this rifle, I've seen claims that the HK300 is capable of 1/4" groups at 50 yards with the right ammo.  It may not be a cheap squirrel and varmint gun, but it sure is a unique and high quality one!

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