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Kel-Tec makes a very innovative rifle called the Sub 2000.  This carbine-style rifle folds in half for easy transport and takes the same magazines as your favorite pistol.  However, this little rifle requires some minor work to improve its overall function.

Disassembly
I first make sure the rifle is unloaded and no magazine is installed.  Then I disassemble the rifle according to my article Kel-Tec SU 2000 Disassembly.

Relieving the Magazine Well
My Sub 2k takes Beretta magazines because I have a Beretta 92FS, but both the factory Beretta and after-market magazines fit very tightly.  I relieved the magazine well on both receiver halves as follows:

I completely disassembled the rifle, then wrapped a piece of 400-grit wet/dry paper around a magazine.  I carefully sanded the rails inside the magazine well on each side of the receiver.  I put the receiver halves together with the screws and magazine catch to test for functioning.  I also beveled the edge of each magazine where it met the magazine catch.

Working the Hammer and Sear
Caution:  This procedure requires special tools.  Unless you are familiar with working with hammers and sears, please do not attempt these procedures.

Required Tools
Please do not attempt to cut/polish the hammer and sear mating surfaces without the correct tools.  Without the correct tools you could round the surfaces making them unsafe and/or inoperable.  I used the following tools to modify the hammer and sear.

As mentioned on the KTOG bulletin board ( http://www.ktog.org ) the sear of the Sub2k rifle is set at a positive angle, i.e. when the sear moves forward it actually has to force the hammer up against the hammer spring.  This is one reason for the very heavy trigger pull.  Also, the sear-to-hammer mating surface is about .060” deep.  In this procedure I will zero the sear angle and reduce the amount of sear-to-hammer mating surface.  Please be aware that the only way to change the angle of the hammer and sear mating surfaces is with the proper tools.  Ok, enough harping!

Hammer/Sear Basics

How the hammer and sear mate is critical to firearm safety, and directly affects trigger pull.  The above figure shows a hammer and sear with a positive engagement angle.  (The angle in these diagrams has been exaggerated for clarity.)  The angle is in front of the hammer pivot point.  When the sear rotates toward let off, it pushes the hammer up against the hammer spring making the trigger pull heavy, but very safe; the hammer cannot accidentally fall off the trigger.

If the sear angle is in line with the hammer pivot point, this is a sear angle of 0^o as shown in the above figure.  Notice that when the sear rotates, the hammer stays in place.  This makes for a light, smooth trigger pull.  The depth of the sear engagement controls creep and let-off.  The deeper the sear engagement, the more drag or “creep” in the trigger because it takes longer for the hammer to release.

If the sear angle is behind the pivot point, this is a negative engagement angle, as shown in the above figure.  This results in a very light trigger, but it can be unsafe as jarring the firearm could cause the hammer to slip off of the sear.  The pressure of the hammer pressing against the sear could cause the sear to move forward releasing the hammer.

It seems that the Kel-Tec Sub 2000 hammer is at 0^o but the sear is not.  This still causes some hammer push through, causing a heavy trigger.  However, there are enough manufacturing variations that you need to check each individual hammer and sear.

Measuring Angle of Hammer Mating Surface

I set the hammer on top of a straight edge so the mating surface was parallel with the edge.  If the straight edge bisected the middle of the hammer pivot hole, the angle was already set to 0^o.  If the hammer was not already at 0^o then I would have to correct it first before working on the sear.

Setting Sear Angle to 0^o
This procedure requires the Power Custom Series I stoning fixture with MKII adapter.  As mentioned before, the sear is cut at a positive angle causing hammer push through.  I verified this by assembling the hammer bushing, hammer, and sear into the left receiver half.  While looking through the safety hole and putting pressure on the hammer with my right index finger, I rotated the sear away from the hammer and felt for hammer movement.  I needed to adjust the sear until it did not push the hammer against my finger.  I performed these steps only after verifying that the hammer angle was 0^o.

I installed the MKII adapter on the Power Custom Series I stoning fixture and align the 0^o mark to the line as described in the fixture instructions.  Then I set the stone guide elevator until the stone was perfectly flat with the mating surface as described in the fixture instructions.  If there was no hammer push through, I polished the sear with the coarse then fine stones.

If there was hammer push through I marked the sear mating surface with marking fluid.  I then moved the elevator up 4 clicks (1 click is about 1/2^o).  I used a square, coarse stone or coarse ceramic stick and stoned the sear surface until enough smooth surface was showing that will be engaged by the hammer mating surface.  I tested hammer/sear function again looking to remove any hammer push-through.  I repeated the adjust and polish steps until there was no hammer push through then final polished with a square, fine stone or fine ceramic stick.

Hammer
This procedure required the Power Custom Series II stoning fixture with universal adapter.  When performing this process, I frequently checked for fit by installing the hammer, hammer bushing, and sear into the left receiver half with no springs.  I visually checked the hammer and sear mating surfaces by looking through the safety hole in the left receiver half.  Before working on the hammer I needed to modify the Series II stoning fixture and universal adapter.

Modify the Series II Stoning Fixture
In order for the Series II stoning fixture to work with the Kel-Tec Sub 2000 hammer, it must be modified by drilling and tapping a third mounting hole so the stoning guide can be moved farther to the right.

I first moved the stoning guide to the existing far outside hole and locked it in the far right position using the ¼ x 20 hex screw.  I drilled a 13/64” hole into the upright at the far right side of the stoning guide adjustment hole.  After I removed the stoning guide I tapped the new hole with a ¼ x 20 tap.  I set and locked the stoning guide onto the stoning fixture using this new hole.

I installed the universal adapter onto the fixture and used a high-speed rotary tool with a cutoff wheel to cut a slot in the adapter mounting screw.  This will facilitate adjusting the adapter.

Modifying the Universal Adapter
The universal adapter that comes with the Series II stoning fixture needs to be modified to work with the Kel-Tec Sub 2000 hammer.

I ground the shorter, round radius flat so there was enough metal left for the small set screw to function.  This was necessary so the stone did not interfere with the adapter when working the hammer mating surface.

With the B side facing me and the ground edge at the top, I installed a .125 pin into the top hole, then installed the hammer onto this pin so the mating surface was on the right.  I then installed a .187 pin into the larger hole to the right of the hammer and allowed the hammer to rest against this pin.

I installed the adapter onto the stoning fixture so that the ground edge of the adapter was to the right, then installed the clamp block so the hammer did not rotate.

The coarse and fine stones I purchased from Brownells especially for this jig were different widths so I had to adjust the stoning guide so both would fit.  I decided to drill a .094 hole in the adapter in line with the alignment mark.  This will allowed me to duplicate the setup if I wanted to work on another Kel-Tec Sub 2000 hammer.

Setting Hammer Angle to 0^o
I measured the hammer angle as described before.  If the straight edge bisected the middle of the hammer pivot hole, the angle was already set to 0^o.

I set the elevator up 52 clicks from the bottom and adjusted the jig so that the fine stone was perfectly flat against the hammer mating surface as described in the instructions.  This was the reference point.

If the hammer was already set to 0^o I used the fine stone to polish the mating surface.  If the hammer angle needed to be adjusted, I moved the elevator up or down accordingly.  3 clicks is about 1^o of change.  I used the India stone to cut the new mating surface and again used  a straight edge to check for an angle of 0^o.  Once I achieved 0^o I polished with the hard Arkansas stone.

Reduce Hammer Mating Surface
From the factory, the hammer mating surface is about 0.060”.  I wanted to reduce it to 0.020” - 0.030”.  This won’t lighten the trigger pull, but it will make it crisp.

Using a caliper I measured from the front of the mating surface to the top of the hammer.  It should be approximately 1.247”.  I wanted to remove .030” - .040” so the result should be between 1.207 - 1.217”.

Using a high-speed rotary tool with a cutoff wheel I carefully removed metal from the front of the sear mating surface.  I checked frequently for fit.  I made sure to leave enough metal so the sear would positively and safely catch the hammer.  I stopped removing metal when the measurement was reduced to 1.206”.  I then beveled the edges of the hammer mating surface to reduce the width.  This will result in a crisp trigger pull.

I installed the hammer onto the Series I 10/22 adapter and installed the 10/22 adapter on the Power Custom Series I stoning fixture so that the front of the sear mating surface was on top.  I stoned the front of the sear mating surface so that it was square.  I was sure to maintain a round radius.  I then carefully stoned the front edge of the sear mating surface to break the burr raised by the grinding.  I lubricated the hammer and sear mating surfaces with good quality gun oil.

I reassemble the rifle and tested for functioning.  My rifle now has a safe, crisp, smooth trigger pull that breaks at 6 pounds.  This is very acceptable for this type of rifle.

Addendum 2017
There is a company called M.CARBO that is manufacturing after-market parts for the Sub 2000 such as spring and trigger kits.  If you don't have the jigs and don't want to do the work yourself, click on the link above and check them out.