Owners Information for the Clark CrankFire GBM-43

This will be an evolving document and may be a bit disjointed in places. Updated 07/14/2017

Disclaimer and Warranty -

The GBM-43 is a BATF approved non-machine gun. It is constructed primarily out of military surplus parts, provided by the customer, that could be as many as 70 years old. I can in no way be held responsible for the quality, safety or condition of such parts made in Soviet countries during WWII and the Cold War era.

The receivers of these weapons were cut into four sections by unknown persons using a gas welding torch. In many cases significant amounts of metal were removed. Subsequently, These cut sections were welded back together by me using a TIG type welding process, and all possible care. Due to the amount of intense heat that has been applied to these parts, it is impossible to guarantee the structural integrity of the finished receiver. Therefore, these weapons are not guaranteed for actual firing of bullets and are to be considered as display pieces representative of a particular time in history or as blank firing replicas.

With that said, each finished firearm IS tested with full poewr Russian made ammo.

Any after sale modifications to the firearm will totally void any warranty or guarantee.

The use of these weapons with live, full power ammo is at the users risk and responsibility.

I understand that there will be owners who will totally accept the risks and responsibilities involved with live ammo firing in these firearms. I will therefore discuss issues related to subsequant firing and cleaning of these weapons.

In no way should these instructions be considered as approval on my part for the actual live firing of these guns with bulleted ammunition.

My only warranty on these finished firearms is due diligence and an attempt to produce good quality work. I in no way guarantee or warrant anything regarding parts I did not make or modify nor the safety of their use.

On those parts that I did make or modify, I only offer repair or replacement if, in my opinion alone, my work was at fault.

I accept no responsibility for injury, accident or loss of life resulting from actually firing live, bulleted ammunition from one of these firearms. The purchaser, the purchaser's family and all associated parties indemnify me, my associates, my family and my parts suppliers from any loss or injury of any kind and accepts this responsibility by taking delivery and firing such a firearm. No exceptions.

Proper safety procedures must be followed at all times! Safety glasses and protective gloves must be worn when firing due to the possibility of out-of-battery firing. Spectators must stay back 25 feet. Gun Crew members must avoid being on the left side of the weapon in case of a case blowout discharging out of the ejection port!

If this is unacceptable, return the firearm to me, shipping prepaid, and I will attempt to sell the firearm for the customer.

Assembly and dis-assembly

The Goryunov SG series of firearms is simple, rugged and easy to service. With a little practice, you can strip one in a few seconds. With that said, this family of weapons was made by many countries and there are many varriations in design. I will talk in general terms and it is up to you to note if your gun is atypical.

There are many orders for assembling the complete firearm. Here is one suggested order. Hopefully it will save you from having to take things back apart due to forgotten parts.


The rear sight assembly and top cover assembly should not be removed unless replacement is required.

Barrel removal is quick and simple. Move the barrel by opening both parts of the top cover and move the barrel wedge to the left side. Pull the barrel out the front. The wedge may come completely out the left side, but it's really supposed to only come out to the right. Take care to not lose the wedge.

After re-assembling the barrel into the receiver, have the barrel wedge fully to the left side of the slot. Then slide the barrel wedge so that the left side of the wedge is flush with the left side of the receiver (SG-43). If the bolt, carrier and spring are installed, you will have to press back on the barrel hard enough to move the bolt to the rear in order to insert the wedge.

To remove the bolt and carrier, pull out the large pin on the right rear of the receiver (SG-43 style only). A rap with a plastic hammer on the left end of the pin may help get it started. Hold onto the spade grips while pulling out the pin! There is a fairly strong return spring inside. Don't lose the pin.

The spade grips rotate bottom up and out to remove (Sg-43). There is a square lug on the top of the grip housing that locks into a recess under the rear sight. Guide it out while controlling the spring pressure. ON the SGM family. depress the retainer pin in the top latch, slide the latch rearward and rotate the spade grips clockwise 90 degrees. Watch for recoil spring pressure on release.

A gentle pull on the charging handle will remove the bolt and carrier

On re-assembly, make sure that the ejector on the right side of the bolt is fully forward. If your recoil spring has been trimmed for length, put the cut end (open coils) inside the carrier to avoid the spring over riding the guide.

If you remove the bolt and carrier while the Clark CrankFire unit is still mounted to the receiver, you will have a minor problem putting them back in. The hammer sticks out enough to prevent the bolt from going back in. I made a simple tool out of an old screwdriver to depress the hammer and allow the bolt to go back in. Heat the screwdriver to dull red to bend.

See the picture below. The flat piece of 1/8" X 1/4" X 1/2" steel on the tip is to provide good contact with the hammer. The piece of 1/8" square stock on the back side is to position the tip at the right level by sitting on the receiver. It also serves as a fulcrum. Insert the tool into the opening on the top of the receiver. The larger cross piece on the front is unneeded so don't add it.




As usual, I over engineered mine a bit! Anyway, insert it into the receiver from the top and lever the hammer deeper into the FCG box as you press on the rear of the bolt.

The FCG box shouldn't be removed very often in order to prevent wearing out the small 8-32 screw threads in the receiver. Should this happen, they can be drilled and tapped to the next oversize. However, on several models, the FCG must be removed to remove the bolt and carrier.

When closing the top cover, make sure the lug on the bottom of the belt cartridge extractor is in the recess in the top of the bolt and that the barrel wedge is properly positioned..

Lubrication and Cleaning

Being as most, if not all, surplus 7.62X54R ammo is highly corrosive, clean the gun well after shooting as much as one round. Remember to clean the bolt face, the chamber face of the barrel, the barrel, the inside of the receiver around the barrel chamber, the gas port & tube and the flash hider. Even the barrel carry handle gets splattered with corrosive junk from the gas piston relief ports.

Also, the current Russian non-corrosive ammo, such as Brown Bear, is durty as hell and freqient cleaning is also a good idea.

As removing the gas valve from the barrel is difficult, try to flush the valve and valve body well with hot water and dry well. Don't forget to oil well after drying. Using very hot water will speed drying and help evaporate water from cracks and recesses. If it will be a while (never over 24 hours!) before proper cleaning is possible, use a spray bottle of Windex or the like to help remove the corrosive salts left from firing. Follow this with a good drying and a shot of spray oil.

A light coat of white lithium grease on all contact points of the bolt and carrier help the gun cycle well. Especially when the gun is "new " and tight. If you have the CCF (Clark CrankFire) unit off, grease the hammer face, tip and lobes of the cam shaft and the nose (where it lifts the trigger) of the linear cam. The linear cam is the push bar that works with the butterfly trigger. Inspect the inside of the FCG box well as the gus spews dirt everywhere during rapid firing.

Also apply grease to the top of the circular cam where the trigger rides. Otherwise, use gun oil on other friction or wear points.

Loading and firing

Remember - the use of live ammo in these guns is at the sole risk and responsibility of the operator. When rapid firing with the CrankFire system, the use of a thick leather glove on the left hand is mandatory.

Insert the desired number of rounds into a Goryunov metal link belt. The proper cartridge is the Communist block 7.62X54R round. Multiple 25 round belt sections may be linked together using a cartridge to connect the two belts. Make sure the rounds are fully seated in the belt to where the shoulder of the cartridge mates up with the taper in the link. A deep walled socket for support and plastic hammer can be used to seat the rounds. Use the hammer carefully and avoid striking right on the primer. The results of doing this wrong are obvious.

Conventional wisdom says to place the "open" side of the cartridge belt up.

Below is the unit I use. I made it out of a 12" section of aluminum square stock and drilled 5/16" holes every 0.802" along the path I wanted the belt to take.





Clark CrankFire notes

The first thing is think safety! Just bumping the crank handle with it in the wrong position can cause a discharge. The safety on the top of the CCF box will block the butterfly trigger and prevent crank rotation. The safety will only work with the hammer fully cocked and the cams not putting pressure on the trigger system. To ensure that the rotary cam is in the correct position for safety engagement, CAREFULLY and gently, rotate the crank handle backwards (Clockwise) until you feel resistance. Then engage the safety.

For very obvious reasons, have the muzzle pointed in a safe direction while putting the safety on or off!

As with all safeties, test them often and never totally trust them. Using your brain is always the best safety.

Unload the firearm if you stop firing. Open the top cover, remove the belt and clear the chamber.

The crank only turns in the counter clockwise direction. Do not try to force it the other way. If it doesn't turn freely and easily, something is wrong. You can use either the butterfly trigger or the CCF interchangeably. Nothing needs to be switched or changed.

If you disassemble the gun, on re-assembly, check to make sure that the "linear cam" that is actuated by the butterfly trigger and runs along the left side of the receiver is properly butted up to the corresponding arm on the butterfly trigger unit.

Remember, the Gory only cycled at 600 RPM in its full auto mode. Most likely, it will not fire this fast in the semi auto configuration due to additional friction associated with the hammer being re-cocked.

It is quite possible to "over-run the crank" by turning it too fast. You will know when you reach this point as the gun will start skipping shots. These are not misfires, the gun just doesn't fire until the FCG mechanics catch up and the disconnecter releases the hammer. Just slow down a bit and all should work fine. The best technique is to start nice and slow and build up to a reasonable speed.

If you do have a miss-fire, jam or other malfunction STOP! Open the top covers and remove the belt. Cycle the bolt a couple of times if possible. Remove the barrel and look down the bore to ensure it's clear. Then re-assemble and start over.

You should have a broken case extractor in case of a cartridge case separation. These can happen due to the thin steel cases used with this ammo. If these happen very often, you have a headspace problem. If it's with one of the guns I built and a barrel I hand fitted contact me. I have the serial numbers for all barrels I install recorded in my records. If this is with a barrel you got from somewhere else, I offer ABSOLUTELY NO WARRANTY FOR ITS USE.

Parts Interchangeability

In theory, parts from all of these guns should interchange. Reality is, many will not. The reason is that after cutting up and re-welding the receiver, many internal parts require a fair amount of hand fitting in order to work properly.

The barrels are the least likely to interchange due to head spacing issues. The bolts and bolt carriers also usually need a lot of polishing and sanding to gain adequate clearance. Most small and external parts should interchange just fine. Installing and using parts not properly fitted by me voids any and all warranties and I deny any responsibility for injuries or losses that could happen due to their use.

Troubleshooting

In the process of building 30 or so of these guns so far, I've run accross several issues that bear passing on.

Chipping, denting or damage to the front surface of the Clark CrankFire box:

If your gun is showing damage to the outside front surface of the FCG box it's most likely coming from empty cases being ejected so forcefully that they are flying rearward and hitting the FCG unit. The most common cause is the gas regulator on the barrel being set too high. "1" is the minimum and preferred setting. If your barrel is set above that you should try a lower setting.

To set the regulator, first carefully pry out the wire circlip that goes around the end of the gas valve. Then support the barrel and pound the regulator out using a brass hammer. When taking it out, clean it well, polish off any rust without removing any metal as this will cause gas leaks. Put a light coat of anti-seize grease on it and pound it back in. Take care to line up the notch in the valve with the rivet head on the regulator body.

The "1" setting is the lowest power and the "3" is the strongest. The number should line up with the straight line stamped on the side, at the rear, of the gas regulator body.

If this doesn't cure the problem, obtain a new recoil spring from me and try using 5 more coils in the length. If the gun runs sluggish or fails to eject, cut one coil off and try again. Keep doing this until you reach a good compromise.

Damage to internal parts in the CCF unit:

A few guns have had issues with the hammer being driven too far back into the FCG box when the bolt recoils. This can cause bent or broken cross pins, damaged hammers and disconnectors. If you are having any of these issues please contact me at:

gclark@gunbuilds.com

More issues will be added to this list as I become aware of them.



Several parts of these guns are modified so that original full auto parts cannot be substituted in an attempt to return the gun to full auto status. Such re-conversion is a Federal felony and will result in the gun being confiscated and destroyed, the owner fined and possibly sent to Federal prison.

Copyright Gregory Clark 2012/2017. Duplicating this one single page, in its entirety, unaltered and free of charge is permitted. Alteration not allowed.