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View Full Version : CETME - G3 trigger pack FCG F/A to S/A modification


MisterJG
April 07, 2004, 21:06
Since G3 build info is pretty limited I will be documenting my build. This build process will take me awhile due to other committments (family, work and stock making). Keep in mind this is my first attempt at building a rifle from the HK family of weapons. So following (using) this information is at your own risk!!! Feel free to add any addition information or comments as this info. will assist everyone.

My build will be consisting of the following:

FMP G3 parts kit from FAC Model# KI403
G3 FCG modification kit from FAC Model# G3-MOD
FMP/SW (U.S. made) receiver from FAC
Hammer & Sear kit (U.S. made) from FAC
JLD 3pc furniture set (U.S. made) from FWRA
JLD Cocking handle (U.S. made) from FWRA
G3 Muzzle Brake (U.S. made) from Jayson at IGF

I will start my documention with the required modifications to the Fire Control Group. In this process I will be removing the F/A capablity of the F.C.G. as per B.A.T.F. regulations.

I highly recommend the FAC FCG modification kit. It contains 3 pcs. A metal shelf for the trigger frame/pistol grip frame. A metal plate for the FCG frame. And a trigger stop pin. These items can be easily made, but the the instructions and templates are well worth the $17.95.


Here is a view of the kit:

MisterJG
April 07, 2004, 21:10
To start I removed the FCG assembly from the Pistol grip frame by removing the selector. The FCG will slide right out once the selector has been removed.

Here is a view of the FCG:

MisterJG
April 07, 2004, 21:17
Now I need to disassemble the FCG by removing the pivot pins for the trigger, trip lever/safety sear assembly and hammer. Use a drift or punch to work them out. The pins should come out with little force, they do have some spring tension on them. The ejector has a small wide head pin. This pin will only come out only from the exterior side of the frame.

Here is a few of the disassemble FCG assembly:

MisterJG
April 07, 2004, 21:22
These items will no longer be used. The sear/trip lever/ spring guide assembly on the lower left will no longer be used on the most part, but the spring guide will. The remaining perts will be discarded.

MisterJG
April 07, 2004, 21:27
Next I need to cut out the forward lower section to remove the sear pivot pin and to allow for clearance for the receiver shelf onto which the pistol grip frame attaches to the receiver.

Here is a view of the area to be removed:

MisterJG
April 07, 2004, 21:32
Here is a view of the finished cut. I used a 4" grinder with a cut-off wheel. You can use any method you see fit (i.e. Dremel, hack-saw). Cut as close as possible and finish off with a file to obtain the correct height.

MisterJG
April 07, 2004, 21:37
Next I positioned and fitted the flat piece of metal that came with the G3 MOD kit. This piece of metal will need to be welded in place and will form a flat shelf.

Here is a photo showing the plate fitted, clamped and awaiting welding. I will be using a MIG welder to weld the plate in.

MisterJG
April 07, 2004, 21:38
Here is a view of the plate after welding

MisterJG
April 07, 2004, 21:40
Next I cleaned up the weld with my grinder and polished it up with a orbital sander

MisterJG
April 07, 2004, 21:43
I then doubled checked my finished demension with a micrometer. The goal was .400", my finished number was .4005". Not to shabby if I say so myself.

MisterJG
April 07, 2004, 21:47
The next step is to install a internal trigger stop pin. The purpose of this pin is to prevent over traveling of the trigger past the point at which the sear can no longer catches the hammer.

Here is a view of where the pin will be located:

MisterJG
April 07, 2004, 21:49
The pin will be welded in place with a single tack-weld.

MisterJG
April 07, 2004, 21:51
Next I ground down spot/tack weld down flush

MisterJG
April 07, 2004, 21:59
Next I will be drilling a new pivot pin hole for the installation of the new sear reset spring assembly.

Here is where I will be drilling the hole (#7):

MisterJG
April 07, 2004, 22:05
Now that I have drilled the hole, I need to make a new sear spring return assembly. The parts consist of the following: The original spring guide, pivot pin, an AR-15 trigger return spring and two spacers. I made the spacers (just under 1/8" thick each) from two nuts which I bored out for the pivot pin and I rounded them for cosmetic reasons on my bench grinder.

Here is a veiw of the pieces:

MisterJG
April 07, 2004, 22:07
Here is a view of a mock-up of the sear spring assembly

MisterJG
April 07, 2004, 22:09
I tried to re-form the original sear spring but it is way to fragile. This is a view of what happened to the spring. From what I've read it is a common occurance.

MisterJG
April 07, 2004, 22:13
Now it's time to reassemble the now semi only FCG. Here is a view showing the new sear return assembly. Note how the spring loop engages the sear perfectly, as if Colt made this spring for this application.

MisterJG
April 07, 2004, 22:25
I hope this info. can be useful to others. I really recommend the FAC G3 MOD kit. The instructions and templates are well worth the $17.95. With the aid of the templates I had the FCG modified in less than 1 hour.

My next segments will be as follows:

2) Prepping of the barreled trunion for the SW/FMP receiver.
Link: http://www.falfiles.com/forums/showthread.php?s=&threadid=109042

3) Modifing the pistol grip frame for the S/A receiver w/ the fake take down pin look.

4) Installation (welding) of the barrel tunnion and cocking tube.

5) Installation of a paddle magazine release to B.A.T.F. specs.

6) Final assembly and headspace (bolt gap check)

Scott S
April 08, 2004, 09:34
Outstanding documentation! Thanks for posting.

wonderful_one
April 08, 2004, 09:41
Bravo, excellent presentation.
Can't wait to the the grip frame mods and the rest.

cliffy109
April 08, 2004, 09:45
When you finish, somebody needs to sticky all of them under a single topic. That is an extremely well done explanation.

ratas calientes
April 08, 2004, 09:49
Super information. Thanks. :bow:

MarkBall
April 08, 2004, 10:34
Great. I just finished 3 FAL's........

Now I want to do a G3............

This thread is like having the instruction book right there in front of you.

Great job Jesse.

Mark

MisterJG
April 08, 2004, 12:08
Thanks for all the great feed back. Feel free to add comments or additional info. as it will benefit everyone!

I will be sending out for my receiver, hammer & sear from ORF. So until then It's a waiting game.

Why is it everytime I'm about to buy a new gun, receiver or parts kit the wife just happens to have a bill that just needs to get paid? How do our ladies know when we have that little extra stash of expendable funds? :cry:

I will keep you guys posted!!!

Lockbar
April 08, 2004, 20:05
JG, you represent the best of what a website should be like. A sincer person, using their valuable time to help and inform other like minded people like us. Thank you for your excellent illustrations and diagrams :)

WyrTwister
April 09, 2004, 16:05
Originally posted by MisterJG
Since G3 build info is pretty limited I will be documenting my build. This build process will take me awhile due to other committments (family, work and stock making). Keep in mind this is my first attempt at building a rifle from the HK family of weapons. So following (using) this information is at your own risk!!! Feel free to add any addition information or comments as this info. will assist everyone.

My build will be consisting of the following:

FMP G3 parts kit from FAC Model# KI403 $198.95
G3 FCG modification kit from FAC Model# G3-MOD $17.95
FMP/SW (U.S. made) receiver from ORF $165.00
Hammer & Sear kit (U.S. made) from ORF $45.00
JLD 3pc furniture set (U.S. made) from FWRA $29.00
JLD Cocking handle (U.S. made) from FWRA $10.00
G3 Muzzle Brake (U.S. made) from Jayson at IGF $40.00

I will start my documention with the required modifications to the Fire Control Group. In this process I will be removing the F/A capablity of the F.C.G. as per B.A.T.F. regulations.

I highly recommend the FAC FCG modification kit. It contains 3 pcs. A metal shelf for the trigger frame/pistol grip frame. A metal plate for the FCG frame. And a trigger stop pin. These items can be easily made, but the the instructions and templates are well worth the $17.95.


Here is a view of the kit:



I have a couple of questions .

How is the trunion attached to the barrel & is this something that has some adjustment ( for H/S - bolt gap ) ?

How iw the barrel / trunion attached to the receiver ? If it is welded to a sheet metal receiver , how about the rifles with the Al receivers , that FAC used to sell ?

How iw H/S - bolt gap set when the barrel & trunion is installed in the receiver ?


God bless
Wyr

MisterJG
April 09, 2004, 16:24
Wyr,

The barrel is pressed and pinned to the trunion. The positioning of the barrel in the trunnion has a direct affect on the headspace as the bolt rollers engage and lock onto the trunnion. The trunion is spot welded at 4 locations around the front end of the sheetmetal receiver and two beads of weld where the stamped bolt carrier rails on the receiver meet the rear of the trunnion. On the FAC alum. receivers you have to epoxy and pin the trunnion onto the receiver.

Here is a photo of the barreled trunnion:

762minigun
April 13, 2004, 04:57
outstanding:whiskey: :whiskey:
This is definatly sticky worthy

mribley
April 13, 2004, 08:46
Just finished my trigger package, the AR spring idea saved my life. Receiver gets here on Thursday. Then the fun begins. So far so good.
Great info on this thread.
MJR

BRM308
April 13, 2004, 11:35
You also might want to post this at HKweapons systems forums. Questions about builds and mods are brought up all the time. Very good executionBTW

MarkBall
May 09, 2004, 22:35
Just a bump for Jesse.

Hot my G3 kit, modified it as your instructions show. The instructions from FAC on the mods to the trigger pack were hard to follow.

BTW, I can't find many US compliance parts for the G3. Any ideas? FAC has some, ORF has some of the same. Seems the main ones are
1. Hammer
2. Sear
3. Cocking Handle
4. Pistol grip
5. Receiver
6. Muzzle device
7. Magazine floor plates & followers

Course a person could get a US Trunion, but then you have to press the barrel off & onto the new trunion. Not much fun & hard to show to an inspector. I like the green furniture - especially the wide forarm & adding a bipod.

Is the buttpad considered a compliance part? Or where could a person get the green US furniture?

Mark

schjims
May 10, 2004, 05:15
Nice job, I have bought the kit from FAC and without a mig..im lost...what will you charge me to do mine?...drop me a line..Schjims@Hotmail.com thanx

MisterJG
May 11, 2004, 01:53
Link to segment #2: http://www.falfiles.com/forums/showthread.php?s=&threadid=109042

MarkBall
June 22, 2004, 09:37
A bump for Jessie. He also has this printed in the FAC catalog.

Way To Go Jessie!! :bow: :bow: :bow: :bow:

IVIETAL IVIan
November 04, 2004, 22:15
OK I can clearly see where you use the pin and small metal shelf for this mod. But what of the step looking shelf? This comes with the G3 mod kit no doubt. But where does it go? I will be making all these parts. Very simple for me, I just can't seem to see where that one part goes!!!??

Also. The parts you removed from the FA assembly; is the sear replaced by a S/A sear? Or are you just excluding it altogether?

I just got all my parts prepped from your first(or second) tutorial, I just want to make sure I am not missing anything!!!!

Frickin OUTSTANDING thread!!!!! When I get my HK51 finished I'll post pix!!!!

http://www.fredsfirearmservice.com/rifleman.gif

MisterJG
November 05, 2004, 00:39
I'll be posting segment # 3 within the next few days

saintarctangent
July 09, 2005, 12:38
FAC is out of business, so I can't order the trigger conversion pieces anymore. Can some provide me the dimensions I need to make my own blocks that get welded into the FCG?

MisterJG
July 09, 2005, 13:18
E-mail sent with drawings.

BTW- Is there a market for such a kit?

I can have my machinist run a batch of these if there is enough interest.

Let me know.

saintarctangent
July 09, 2005, 13:23
For the trouble of making your own, buying a set from FAC for what, $17 sure was more convenient.

Not sure how many others would want to buy one if you made a run of them, but I would be in the market for a few.

gw11
August 07, 2005, 12:21
Jesse
Thanks for all the documentation. I do have a small question though!


[[ EDIT to add: If this info screws up you domentation and you want it deleted I will gladly do so ! George]]



For the height of the Sear return spring hole, you have it as 3/16" above the tab line.
To my understanding it should be .100" below the trigger hole center which puts it at .063 above the Tab line. I have the drawing that is in the background of one of your pics and it isn't very good. I do have another drawing from Dan Coonan that is a bit more descriptive
Below I show the pic [ I took all the dimensions from the upper one which is exactly to size for overlay and back checked the lower drawing] Some of the dimensioning and poor spelling is mine, but it is correct.

Does your method possibly help with spring tension?

gw11

gw11
August 07, 2005, 12:22
and

gw11
August 07, 2005, 12:22
last

gw11
August 07, 2005, 12:48
Below is a copy of a letter to Jason at IGF on the mods needed. They are real close to my dimensions since I converted the drawing dimensions with relationship to a couple of trigger packs I had.

To add to this I just received a trigger pack I sent out for upgrade and a trigger job. And it had the Sear spring hole at .160 from the bottom of the frame. Perhaps none of this is important!?

Although I would tend to side with the ATF!!!!

gw11



Department of the Treasury

Bureau of Alcohol, Tobacco, and Firearms

Washington, DC 20226

Sept 28, 2001



Mr. Jason Cotter

Mountain Home, AR 72653



Dear Mr. Cotter

This is in reply to your letter in which you have requested proper procedure for modifying a Heckler and Koch G-3 machinegun trigger, into a semiautomatic trigger.

To properly convert a G-3 machinegun trigger into a semiautomatic only trigger there are several modifications needed. The modifications are listed as follows:

1. Remove the automatic sear.

2. Grind off the automatic sear notch from the face of the hammer

3. Cut away the front corner of the trigger housing where the automatic sear is mounted, .410-inch from the bottom and .540 inch from the front towards the rear.

4. A new hole has to be drilled to accommodate the trigger spring. The hole dimension is .200 inch drill that hole .165 inch from the front of the new corner and .250 from the bottom of the new corner. These dimensions are for the center of the hole.

5. The trigger spring should be replaced with a semiautomatic trigger spring but the G-3 trigger spring will work.

6. The trigger over travel stop has to be moved towards the rear tang of the trigger .150-inch

-2-

Mr. Jason Cotter

7. It will also be necessary to modify the trigger housing. Modify the housing by cutting off the tabs for the front assembly pin. Then adjust the fit of the housing into the receiver.

Title 26, United States code, Chapter 53, section 5845 (b), defines the term machinegun as any weapon which shoots, is designed to shoot, or can be readily restored to shoot, automatically more than one shot without manual reloading with a single function of the trigger. The term shall also include the frame or receiver of any such weapon, any part designed and intended solely and exclusively, or combination of parts from which a machinegun can be assembled if such parts are in possession or under control of a person.

If you do not properly modify the G-3 machinegun trigger pack and install it in your semi automatic rifle, and that weapon fires more than one shot automatically with a single function of the trigger, you would be in possession of an unregistered machinegun.

We trust that the foregoing has been responsive to your inquiry. If we can be of any further assistance, please contact us.



Sincerely yours,

Curtis Bartlett

Chief Firearms Technology Branch

kevin917z
August 15, 2007, 20:09
this has been a long time ago but are there plans to finish this tutorial? im interested in how to weld the g3 up correctly so everything will work right

melvin
February 16, 2008, 10:48
I recently bought a G3 kit and have no clue how to build it. Does anyone make a US made trigger pack with everything already assembled that I can just drop in. Thanks

maurice05
February 16, 2008, 12:31
can you order one from JLD

Fordf150-1
February 27, 2008, 10:50
ORF has the receivers and flats as of 2-24-08

gunplumber
February 27, 2008, 11:28
that AR trigger srpring is a great idea, I'm tired of breaking the factory ones trying to reshape them.

K.O.A.M.
February 27, 2008, 12:50
I was able to buy the housing, hammer, trigger, sear, trunnion, and pistol grip from JLD. I bought the receiver from Vector. I didn't like the JLD furniture, so I sent more expensive parts to GP to build for me.

ftierson
February 27, 2008, 13:01
Although this is a little off topic and I can easily delete it if you all don't want it here, I just wanted to mention that Century Arms is advertising a couple of different armorer's kits for the CETME rifle that can be quite helpful.

I picked up one of the two different 'kits' at a local gunshow (for $250). The ten brand new CETME mags alone were worth that to me. But the 'kit' also contains essentially all of the parts, usually many times over, for the CETME (it was designed to support 100 rifles in the 'field').

In the one that I picked up, all of the parts were brand spanking new...

But more to the point here, it also contained a new, complete trigger pack, so you have another to replace the one that you first screw up when doing the FA to SA conversion...:)

For what it's worth...

Forrest