Help with STG needed

Scott V2 · July 05, 2003, 18:56

This is my first FAL

It is a premium STG kit built on a Coonan receiver.

I took it out for the first time this weekend to get the feel for it. I encountered some setbacks which I need help with.

First, the bolt carrier would frequently not close all of the way. This would occur when letting the carrier slam forward on a fresh magazine, it may have happened in firing sequence once or twice as well.

Second, the end firing pin nipple broke off of the bolt after 350 rounds. Upon disassembly of the bolt, I also discovered that the firing pin had broken inside the the bolt. This must have happened earlier because the break inside was mushroomed from hitting itself. This ended the day since I do not have a replacement with me.

What is going on that I need to fix?

Here are some things about the gun:

It is all matching numbers, looked almost new when I got the kit.

All parts are original except the h/t/s which are FSE, Tapco gas piston, Tapco pistol grip, and obviously the Coonan receiver.

I used 6 different mags, one which seemed to have the most FTF was put away, the rest would have the same occasional problem with the carrier not closing all of the way.

The bolt always picked up a fresh round.

The bullet noses on some of the rounds which did not allow carrier to close were deformed from the ordeal.

Gas setting was at 3.5

SA ammo was used.

There is no discernable friction when sliding the bolt carrier manually through the rails and dust cover.

When no hiccups occurred, firing 20 rounds as fast as the finger is a whole lot of fun!

Any help, links would be appreciated. I don't have the ability to post pics right now to show what is going on. I also may not be able to get back to a computer until Monday morning to answer questions.

cadillac · July 05, 2003, 21:14

Are you sure it is properly head spaced?

**W.E.G.** · July 05, 2003, 21:42

Quote:

Originally posted by Scott V2
...the bolt carrier would frequently not close all of the way...The bolt always picked up a fresh round...The bullet noses on some of the rounds which did not allow carrier to close were deformed from the ordeal.

Are these rounds slamming nose-down into the receiver, without entering the chamber?

In any event, it is always a good idea to polish the receiver rails.

shootist87122 · July 05, 2003, 22:03

Possible weak recoil springs and or gas not regulated properly. Try new recoil and gas piston springs.

Gas: When loading one round at a time (from magazine) does the bolt lock open? The gas system should be a free of oil as possible after cleaning.

More Gas - Did you check to see that the gas port is clean. Remove fron sight and run a small wire (paperclip) through the gas block and into the barrel to clean out any old cosmo or fouling.

Possible ammo problem: How far is it throwing the brass? Is it fairly consistant (say 6-10 feet) or do you get some weak ejections (not the Viagria kind) mixed in?

Possible mag problems - I have one (Tapco Used) mag that does this to me after the gun gets a little dirty. I think I'm gonna use it for a target next time.

Gas Piston Rubbing? - does the gas piston run smoothly (by hand) with the piston spring removed?

More Gas - Is the gas piston original or aftermarket? Check to see if correct length - it needs a tiny bit of jump, some aftermarket ones are a hair too long.

Upper receiver / magwell - See if you have rough edges where the cartridge feeds through the Upper when being stripped by the bolt.

Court in Fl · July 05, 2003, 23:47

First, the bolt carrier would frequently not close all of the way.

Could be a lot of things, but one thing I ran in to on
my last STG build was the FSE hammer was shaped a little diffrent
at the top of the hammer from the factory hammer and would sometimes catch on the underside of the bolt carrier and stop the movment of the carrier.

I ground the hammer to a diffrent shape and all was fine after that.

If this is your first build you could have more than one problem
stoping your rifle from functioning.

When you sighted it and ZEROED it was the rear sight more on one side than the other (left or right) ?

Did you use headspace gages to set the headspace?

Is the gas piston moving freely in the gas tube and into the receiver ?

Did you adjust the gas regulator ? Is the gas plug set for auto ?

We want to help, give us as much info as you can.

Court in Fl.

Scott V2 · July 07, 2003, 06:12

I am back home and able to reply now.

Cadillac,
the kit was assembled for me by a gunsmith from the Files, it was headspaced. The build was done right, it just is hiccuping a bit.
BTW, it was you Caddy who recommended Jeff for a source for kits, you are directly responsible for all of the fun I had this past week with the new toy!

Thanks

Gary,
The bullets are entering the chamber, I plan on polishing both the rails as well as the feed ramp. I also found what I think is the main culprit, will note below.

Shootist,
I believe the gas setting is about right, I was getting consistent ejections 10-15 ft . I am going to check the Tapco gas piston for length against the original, thanks for the tip.

Court,
I will check that FSE hammer, that may be part of it. All of the other aspects of your questions were in proper order on the rifle when I was using it.

Update on what I have found:

My kit was so unused that the bolt carrier had an almost untouched park finish on it. Since it wasn't shutting all the way (sometimes would miss by .25 inch) I figured it would show signs of where the problem may be. I wish I had a camera to show all of you.

On the front lower left side of the bolt carrier is a wear mark almost the exact same size as the distance the carrier fails to close. (Note that this failure to close happened almost exclusively while chambering the first round out of a mag.) I then check the inside rail of the receiver and discovered an almost identical wear mark where the carrier should be when fully closed. There is an ever so slight variation in height where the machining was done. I think this may be the main culprit. I took the bolt out of the carrier and pushed the carrier back and forth in the receiver, it did not bind at all. BUT, I pushed on the carrier unevenly and got it to "bump" on the suspect area. I think this is it.

Should I:

A. file this area down
B. put lapping compound on it and cycle it a million times
C. get stronger springs for recoil tube?

Any ideas on how I broke the firing pin in two places?
Thanks for all your replies
-Scott

ce · July 07, 2003, 14:07

File that area down and see if you can duplicate the slo-mo hiccup.
It voodn't hoit.

shootist87122 · July 07, 2003, 15:43

Quote:

Originally posted by Scott V2
This is my first FAL

It is.........built on a Coonan receiver.

There ya go!

I think Court diagnosed the same somethin rubbing against somethin problem a week or two back. Left inside of receiver needed relieving a bit (IIRC).

Bwana John · July 09, 2003, 10:48

When my one-piece firing pin broke the tip of the pin stuck out of the firing pin hole in the bolt face, and didnt retract, causing the bolt and carrier not to go compleatly in to battery. Problem fixed be new 2 piece firing pin. (yours doesnt sound exactly the same, but try fixing what you know is broken first, maby the problems are connected somehow) Broken firing pin is very dangerous!!

July 05, 2003, 18:56	#1
Scott V2 Registered FALaholic #: 10082 Join Date: Mar 2003 Location: Ohio, in a van by the river Posts: 2,225	Help with STG needed This is my first FAL It is a premium STG kit built on a Coonan receiver. I took it out for the first time this weekend to get the feel for it. I encountered some setbacks which I need help with. First, the bolt carrier would frequently not close all of the way. This would occur when letting the carrier slam forward on a fresh magazine, it may have happened in firing sequence once or twice as well. Second, the end firing pin nipple broke off of the bolt after 350 rounds. Upon disassembly of the bolt, I also discovered that the firing pin had broken inside the the bolt. This must have happened earlier because the break inside was mushroomed from hitting itself. This ended the day since I do not have a replacement with me. What is going on that I need to fix? Here are some things about the gun: It is all matching numbers, looked almost new when I got the kit. All parts are original except the h/t/s which are FSE, Tapco gas piston, Tapco pistol grip, and obviously the Coonan receiver. I used 6 different mags, one which seemed to have the most FTF was put away, the rest would have the same occasional problem with the carrier not closing all of the way. The bolt always picked up a fresh round. The bullet noses on some of the rounds which did not allow carrier to close were deformed from the ordeal. Gas setting was at 3.5 SA ammo was used. There is no discernable friction when sliding the bolt carrier manually through the rails and dust cover. When no hiccups occurred, firing 20 rounds as fast as the finger is a whole lot of fun! Any help, links would be appreciated. I don't have the ability to post pics right now to show what is going on. I also may not be able to get back to a computer until Monday morning to answer questions.

July 05, 2003, 21:14	#2
cadillac Registered FALaholic #: 3235 Join Date: May 2001 Location: Lincoln County, MT Posts: 3,495	Are you sure it is properly head spaced? __________________ United We Stand - Falaholics One and All

July 05, 2003, 22:03	#4
shootist87122 Registered FALaholic #: 7202 Join Date: Aug 2002 Location: NM Posts: 5,126	Possible weak recoil springs and or gas not regulated properly. Try new recoil and gas piston springs. Gas: When loading one round at a time (from magazine) does the bolt lock open? The gas system should be a free of oil as possible after cleaning. More Gas - Did you check to see that the gas port is clean. Remove fron sight and run a small wire (paperclip) through the gas block and into the barrel to clean out any old cosmo or fouling. Possible ammo problem: How far is it throwing the brass? Is it fairly consistant (say 6-10 feet) or do you get some weak ejections (not the Viagria kind) mixed in? Possible mag problems - I have one (Tapco Used) mag that does this to me after the gun gets a little dirty. I think I'm gonna use it for a target next time. Gas Piston Rubbing? - does the gas piston run smoothly (by hand) with the piston spring removed? More Gas - Is the gas piston original or aftermarket? Check to see if correct length - it needs a tiny bit of jump, some aftermarket ones are a hair too long. Upper receiver / magwell - See if you have rough edges where the cartridge feeds through the Upper when being stripped by the bolt. __________________ "So in the Libyan Fable it is told, That once an eagle, stricken with a dart, said, when he saw the fashion of the shaft, it is by our own feathers, not others hands, are we now smitten." -Aeschylus

July 05, 2003, 23:47	#5
Court in Fl Curio & Relic FALaholic #: 5046 Join Date: Dec 2001 Location: South Florida Posts: 3,150	First, the bolt carrier would frequently not close all of the way. Could be a lot of things, but one thing I ran in to on my last STG build was the FSE hammer was shaped a little diffrent at the top of the hammer from the factory hammer and would sometimes catch on the underside of the bolt carrier and stop the movment of the carrier. I ground the hammer to a diffrent shape and all was fine after that. If this is your first build you could have more than one problem stoping your rifle from functioning. When you sighted it and ZEROED it was the rear sight more on one side than the other (left or right) ? Did you use headspace gages to set the headspace? Is the gas piston moving freely in the gas tube and into the receiver ? Did you adjust the gas regulator ? Is the gas plug set for auto ? We want to help, give us as much info as you can. Court in Fl. Last edited by Court in Fl; July 06, 2003 at 01:58.

July 07, 2003, 06:12	#6
Scott V2 Registered FALaholic #: 10082 Join Date: Mar 2003 Location: Ohio, in a van by the river Posts: 2,225	Back home again I am back home and able to reply now. Cadillac, the kit was assembled for me by a gunsmith from the Files, it was headspaced. The build was done right, it just is hiccuping a bit. BTW, it was you Caddy who recommended Jeff for a source for kits, you are directly responsible for all of the fun I had this past week with the new toy! Thanks Gary, The bullets are entering the chamber, I plan on polishing both the rails as well as the feed ramp. I also found what I think is the main culprit, will note below. Shootist, I believe the gas setting is about right, I was getting consistent ejections 10-15 ft . I am going to check the Tapco gas piston for length against the original, thanks for the tip. Court, I will check that FSE hammer, that may be part of it. All of the other aspects of your questions were in proper order on the rifle when I was using it. Update on what I have found: My kit was so unused that the bolt carrier had an almost untouched park finish on it. Since it wasn't shutting all the way (sometimes would miss by .25 inch) I figured it would show signs of where the problem may be. I wish I had a camera to show all of you. On the front lower left side of the bolt carrier is a wear mark almost the exact same size as the distance the carrier fails to close. (Note that this failure to close happened almost exclusively while chambering the first round out of a mag.) I then check the inside rail of the receiver and discovered an almost identical wear mark where the carrier should be when fully closed. There is an ever so slight variation in height where the machining was done. I think this may be the main culprit. I took the bolt out of the carrier and pushed the carrier back and forth in the receiver, it did not bind at all. BUT, I pushed on the carrier unevenly and got it to "bump" on the suspect area. I think this is it. Should I: A. file this area down B. put lapping compound on it and cycle it a million times C. get stronger springs for recoil tube? Any ideas on how I broke the firing pin in two places? Thanks for all your replies -Scott

July 07, 2003, 14:07	#7
ce Registered FALaholic #: 373 Join Date: Jul 2000 Location: New Mexico Posts: 5,905	File that area down and see if you can duplicate the slo-mo hiccup. It voodn't hoit.

July 09, 2003, 10:48	#9
Bwana John Registered FALaholic #: 3810 Join Date: Jul 2001 Location: N. AZ Posts: 2,507	When my one-piece firing pin broke the tip of the pin stuck out of the firing pin hole in the bolt face, and didnt retract, causing the bolt and carrier not to go compleatly in to battery. Problem fixed be new 2 piece firing pin. (yours doesnt sound exactly the same, but try fixing what you know is broken first, maby the problems are connected somehow) Broken firing pin is very dangerous!!

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