instrucions50

8/8/2019 instrucions50

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Thank you for purchasing a .50 M2HB Semi Auto conversion kit from Karma Metal Products. You can expect years of trouble free shooting and reliability. Pleaseread the instructions first! These instructions presume you are starting with aparts kit, not an assembled gun.

The following items are included in your kit:

1 Set of instructions. Please follow them closely for your shooting safety.1 Trigger bar with disconnector1 Semi auto sear1 Trigger bar return spring1 Replacement screw for timing screw assembly (The timing assembly is not neededin the semi-auto gun)1 Full auto trigger arm block (This must be welded into place for BATFE Compliance)1 BATFE approval letter. (It would be wise to keep this letter with you/your gu

n, especially when shooting).

All NFA Rules Apply

You will notice I have also included Modification prints for the bolt, barrel extension and the buffer assembly. These are for use with the Karma Metal right hand side plate only. If you are using a different manufacturer, use their instructions to match their side plate. NOT OURS!! Our instructions will cover only the modification required to install KMP trigger bar and sear, and ofcourse the FA trigger block.

Let's get started!

We will start with the top plate, turn it upside down. Look at you bracket assembly. Your cocking lever rides along this bar. It is what cocks your gun. Your semi-auto trigger will straddle this bar. Most bars will need no modifications, but some will. The width of this bar must be .460 (along the entirelength). (Figure A). If it is wider where the cocking lever engages, it must be narrowed to .460 max. Some of these are pretty hard and may need to be groundto the correct width. This operation may be easier to do after welding in thefull auto trigger block. (It gives added rigidity to the bracket assembly).

Let's us do that next. (Figure A-1) The trigger blocks supplied is wider than needed and must be milled or ground to fit tightly in your particular gun

. Keep it as snug a fit as possible. Weld the trigger block in position. It should be flush with the front of the bracket assembly and bolt-hold back springblock. Looking at it from the bottom it should be the same height as the rear section. I used a tig welder and got excellant results. I welded at front and on top. This will prevent the installation of a full auto trigger and keep you in compliance with the BATFE letter.

Next you have to make a small cut at the front right portion of the cocking bar. (Figure A-2). This allows the disconnector to nest out the way prior to firing the gun. Looking at the bottom again of the top plate, you see that the top right hand corner has a slot .100 X .490 X .180 deep. After this cut is done (I suggest you use a carbide end mill) your semi-auto trigger should fit inplace (Figure A-3). You should be able to put your trigger lever through the tr

igger and bar. It should move freely. The disconnector should go into the relief you just cut with no interference.


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Remove the timing nut from the top plate. Your return spring will slideover the stop post next to it in final assembly. We are not ready for that yet. Just giving you a heads up. We are done with the top plate. Your pretty legal at this point. This weapon will not accept a full auto trigger, at least notwith this top plate.

Ok, your trigger fits smoothly with no binding and the disconnector nest

just below the cocking slot, right? See (Figure A-3).

Now we are ready to attack the bolt modification. This is where the funbegins.

The bolt modifications are very important. The first thing to do is-cutthe slot for your new semi-auto sear. Please refer to your illustation #5. The slot is cut in its original position .150 from rear. We are going to widen the channel in 3 places. First we will cut .625 width at the back, down to at least 1.250 from top of bolt. I strongly suggest a carbide cutter in a CNC mill.It can be done on a conventional mill. But these bolts are tough. This is doneon the same center line as original! The sears are cut to .620 so we will cut

to at least .625 min.

The next cut is "The Mother of ALL CUTS". The sear is .750 wide X .120so we need to cut a bit larger to allow the sear to fit in properly. Go slow isall I can advise. Measure twice and cut once. I use a 1/2 X 1/8 carbide key cutter in a CNC mill.

You will notice a .500 X .070 cut also in the sear slot. You may or maynot need this cut. After cutting your .625 and .755 cuts, see if your sear slides all the way to bottom. It should slide up and down with no drag. I've seen1 or 2 bolts that needed additional relief cutting in that .500 area. It really depends on your bolt. If something is hanging up don't force it!!! Try turning sear upside down. Does it go into slot now? If it does chances are the nose

of the sear is being interfered with in that .500 section I told you about. Use good lighting and look. I've seen one that was off center and only needed 1side cut. You have to use your head on this. Also, make sure the sear slides almost all the way down when installed the way it is supposed to go. The sear "ear" will protrude roughly 1/16 (without spring in the bottom of bolt). Once you have the sear sliding smoothly, your done with that portion of the modification.

Next we will cut the right top portion of the bolt. Here, there may bea difference, depending on the RHSP you choose. On the KMP side plate you cutthe corner per illustration #5 (.160 X .070 deep.) If you are using a different RHSP cut per their instructions. Again I suggest carbide. This is a prettysimple cut. Just take it slow.

There, the bolt is finished. If you do use a different RHSP-from KMP'sand want to alter it to fit the above design see print marked Semi-auto RHSP Inside islands, and make the changes to RHSP per that print. You may not be able to, depending on the configuration of islands on your plate.

So you understand the workings of these modifications of the .50. I have included the same drawings I submitted to the ATF. Illustrations #8, showingthe trigger/disconnector prior to firing. Illustration #9 shows the position ofthe disconnector after firing. These two drawings pretty much show how the semi-auto trigger bar & disconnector function. As you are assembling your gun, pay close attention to the little things. Is it square? Are any rivets protruding i

nside the receiver box further than they should be? Due diligence to the smallthings, will make this a much easier job for you.


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If you have ordered a RHSP from KMP you will receive a drawing showing the completed plate. As it would be illegal to supply you with a finished receiver. You will have to finish this on your own. Separate instructions will comewith your plate.

Now let's get to assembling the Trigger & Sear.

For those of you familiar with the 1919, the assembly of the sear in thebolt will look familiar. To those not familiar, here is how it goes. Assembleyour firing pin and firing pin extension (the pin nest in the extension) in thebolt (lube it first). The round part of the extension goes up, the angle part goes down. The little lip facing downward is what grasps your sear. Push themall the way forward in the bolt. Keep the slot perpendicular to the bolt. Place your sear spring in the recess in bottom of the bolt. Next put you semi-autosear in slot, press all the way down. The spring should nest in bottom of the bolt and the bottom of the sear. (That is what the small hole on the bottom is for). Next put the sear stop in. Here is where it gets tricky. Some stops go in from the top of bolt. You push past firing pin spring and (looking at back ofbolt) swing the stop to the left. It will engage in the slot on the LH side of

the bolt. The other common design has a pin with a small rectangle on it. Itslides up from the bottom of bolt past firing pin spring. Then it has a clasp that looks like a small open end wrench that your fit over the pin slot, then moves over to the LH groove in bolt. It doesn't matter which one you use with sear. However, depending on which manufacturer's gun you are building,it will matter which breech block you are using. THIS IS VERY IMPORTANT!!!See Illustation #11. If your sear stop goes in from top of bolt you can use either breech block. If it goes in from bottom, you need a breech block with a recess in it to clear the rectangle on the bottom of your bolt! This is very important. YOUR GUN WILL NOT GO INTO BATTERY IF YOU USE THE WRONG BREECH BLOCK. THISCOULD BE DANGEROUS. Ok, you have the correct one right? Now you should be ableto move your sear up and down with little pressure. Good.

Next install your cocking lever and retaining pin. The cocking lever goes into the top of the bolt in slot beside your sear stop. Flat side forward (FSF), the rounded end goes toward the rear. It is what pulls your firing pin extension back and lets the sear jump up and grab that puppy. The retaining (or pivot) pin goes in the left side of bolt and then the cocking lever. Flat side up(FSU). You should now be able to push your cocking lever forward and the searshould come up to hold the firing pin cocked. Of course, you are doing all thisoutside of the weapon with no ammo in bolt, gun or in the room! To test, put ascrew driver on the ear of sear sticking up above the bolt and press down. Ifit goes "click" you done good. Go ahead do it again. So far so good. Now youcan install the rest of parts in the bolt.

Next the trigger assembly!

Youv'e already installed your trigger in the top plate to check for fit,so this is the easy part. Do it a few times before you assemble your gun so you are familiar with it. You can put the return spring in with the trigger or after you've installed the trigger. It just fits over the post in Top plate and nest in the little counter bore at rear of trigger bar (see illustration # 12 ). The little 6-32 screw acts as an adjustment stop so your trigger won't over travel after your gun is assembled and you have installed the trigger bar. (It iseasier to first install the trigger bar, then the bolt). You really won't needto put the bolt return spring in yet. Place your spade grip on guns. If it doesn't want to go past trigger bar you will have to remove trigger bar and polishthe radius end. (scotch brite wheel is best) We make these as close as possib

le but they may need some fitting. Once you get your spade grip to go into place, charge your weapon (cock it, UNLOADED of course). When you press down on thebutterfly (trigger) does it release the firing pin? You have to set the 6-32 s


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top screw until it just lets the firing pin release. You can roughly do this without the spade grip in place. You'll have to play around with this a bit. Whencorrectly set you can see your disconnector through the top cover with the boltpulled back a bit and the butterfly pressed all the way down. The disconnectorwill not touch the top of bolt. This is correct. When the weapon is charged and the bolt is in battery, the butterfly should then release the firing pin.

Your about ready for the range! If you have decided to use the bolt hold open(BHO) fixture, this is where it gets tricky.On the original full auto youcan slide the trigger bar in and out without removing or replacing the BHO parts. Not so with this semi-auto design. The trigger bar and all of the bolt holdopen parts must be placed in the gun at the same time. It is tricky. Practicewith the parts before you rivet the top plate!! Practice with the BHO, placingparts in the top plate without Helical compression spring.(see BHO picture)

Additional cut: This cut was omitted in original instructions. This has to bedone for the BHO to clear the top of the sear. Please excuse the poor picture,but it is the best I could do. With the BHO sitting on its back as shown in figure #13 mill or grind a .200 wide by .250 deep relief cut. This will allow it t

o clear the trip ear on the sear.

The tech manual TM9-1005-213-25 has a section that really helps. But you needa special tool to compress the spring when it is in gun. Unlike the manual states you cannot drop the latch out of the way and press on the latch bolt. It must be assembled with all the parts and the latch itself must be pressed in so you can install the round nut and cotter pin. All this takes a fair amount of fingers. You'll need help. Make sure everything fits together smoothly before youattempt to put these in your weopon. A note here. When you weld your weopon,if you intend to weld on the inside receiver, the top left corner is where thisassembly rides, so be careful not to put a large weld bead in this corner or the internal parts won't fit. Remember you gotta weld it when it is all done to make the BATFE HAPPY. I hide the welds in slots on bottom plate and at the botto

m of trunnion. Top plate welds are trickier. Just gotta do the best you can.

I've tried to make these instructions as easy as possible. But I'm a machinist not a writer. If you have any questions don't hesitate to email or callme and I'll help you all I can.

There are just a couple more things I'd like to go over with you on thisweapon. Before you put the first bullet in. Become real familiar with this weapon. It is a beauty, but a powerful one. Remember, the range of the weapon isabout 4 MILES! CHECK YOUR HEAD SPACE EVERY TIME YOU TAKE IT OUT. This is veryimportant. If you don't have a headspace gage GET ONE!

There are some excellant manuals on the M2HB, Several places have them.One is Field manual FM23-65. The other is The Technical manual TM9-1005-213-25. In addition Greg Colson sells an excellant CD from General Motors, on the .50. Greg is known as #2 on www.M2HB.net - .50 board. These will help immensely with the function of this fine weapon. I suggest your read them first. Use yourhead and be careful, this isn't a 9MM popper. Make sure everything moves smoothly. Never fire with the cover open! If it does not fire when you put a round in it, but you heard a click, wait for a full minute before opening the bolt to make sure it was not a hang fire. These are very powerful and you don't want itblowing up in your face.

Thanks again, for buying my product. I hope you enjoy it as much as I do mine.

Tom TKMP 419-524-4371


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All NFA RULES APPLYThe buyer accepts responsibility for the legality and safety of this wea

pon. KMP disclaims all other warranties whether express or implied.

And Hey, BE CAREFUL OUT THERE!!!

Additional note: I have included 3 photos of the M2 -vs- M3 Top plate.I show a cut on the M3. If you cut this way you must put in a insert so the c

ocking lever does not catch. Another way of doing this is to remove cocking lever bar and machine the rear bottom portion that contacts the top plate itself.Here again, a insert is made. I suggest screwing these inserts in. That way you can still remove the trigger arm for repair. If you rivet these the inserts in, you will have to drill them out. CAll if you have any further quesions.

**5-16-06 We have added a picture of an M-3 Cocking bar. It shows themodifications I MADE to it, to work in a M-2 gun with bolt hold open.

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