Gas problem!!

[ALMAR]

So i had beans for lunch...ha ha no, seriously


Last time i took my DA m1a to the range it would not cycle. No, not the gas selector thing i tried both possible selections at the range, besides i know the selector’s groove needs to be vertical.

I put the grooved sadlack piston in it so i figured hey easy problem fix, just put the old one back in...still no cycling

The piston, gas cylinder and plug are clean and dry, piston moves in or out freely by tilting. All the ports are open and clean.

Ok...

checked the alignment of the barrel port with the gas cylinder port...perfect...

No jams in the action, all moves smoothly, standard norc ammo, federal too...


What the??

With the grooved sadlack there is nothing, no movement at all, with the OEM piston the is some movement but not enough to eject the round.


All out of ideas here...this is a new problem but again this is not the barrel the rifle came with, my guess is that the port is a little undersized. Any ideas?

 

[45ACPKING]

Loose gas plug?
Does your stock piston drop with vacuum?
Is your gas plug full of carbon?
And lastly, has it previously funtioned normally with that barrel?

And I'll add that U.S. made pistons are undersize for chinese cylinders. They can work but because they are undersize the can chatter and damage chinese cylinder walls.
I've always preached that US gas pistons don't correctly fit in chinese cylinders.

 

[Seafury]

The first time I shot my TRW M14 in the eighties it would not cycle. It had sat for a while and after moving the gas cylinder out of the way and cleaning that tiny little hole in the barrel with a paper clip it never failed to function ever again.

 

[dratt]

Loose gas plug?
Does your stock piston drop with vacuum?
Is your gas plug full of carbon?
And lastly, has it previously funtioned normally with that barrel?

And I'll add that U.S. made pistons are undersize for chinese cylinders. They can work but because they are undersize the can chatter and damage chinese cylinder walls.
I've always preached that US gas pistons don't correctly fit in chinese cylinders.

Thanks I didn't know that, and I almost ordered one.

 

[ALMAR]

All the points mentioned were checked, that was the first time I tried the barrel.
The sadlack seemed to be a pretty close fit and slowly descended when the rifle was tilted but i'll check that out more in depth.
I think that the spec gas port should be 0.076''...I think mine is around 1/16, probably the metric closest to 1/16...

 

[ALMAR]

Well I saw no difference using the calipers but with the micrometer...yeah there is about a 2.5 thou difference...damn. Is this big enough to be a problem if so.... anybody want a sadlack piston?

 

[rodauto]

Well I saw no difference using the calipers but with the micrometer...yeah there is about a 2.5 thou difference...damn. Is this big enough to be a problem if so.... anybody want a sadlack piston?

Now you have an excuse to buy a USGI gas cylinder so the piston will work!!
Rodney

 

[jonh172]

Not the original barrel?
Had this barrel worked and is now not working? Or has this barrel never worked?

With the action closed, how much piston is showing? If it's more than a quarter inch, It's possible the piston itself is cutting off the gas by not lining up properly.

I've had this, and I made a shim to sit under the gas plug to allow the piston to move further forward.

 

[yomomma]

I told you so way back when you bought it.....

The sloted ones are for heavier bullets to begin with.

 

[ALMAR]

Not the original barrel?
Had this barrel worked and is now not working? Or has this barrel never worked?

With the action closed, how much piston is showing? If it's more than a quarter inch, It's possible the piston itself is cutting off the gas by not lining up properly.

I've had this, and I made a shim to sit under the gas plug to allow the piston to move further forward.

What do you mean showing? You mean the piston shaft?

Yomomma, I know..i want the versatility and to experiment and it was the only one available at the time so I just went for it.

I checked the gas port alignment yesterday using a pin with he same diameter as the gas port in the barrel in order to have a better reading on the alignment and there is a little step..so some shims might be good, doesn't hurt to try. With a small pin, all seems perfect but...

This was the first time I shot with this barrel.

I'll probably end up just ordering the whole usgi gas system...damn this money pit!

 

[jonh172]

Yes, how much of the tail of the piston is sticking out of the cylinder that butts up against the op-rod?

 

[ALMAR]

ahhhh yeahhh...that hole in the piston...I didn't think of that. I'll check it out tonight.

edit: I thought about it and it cant be that, the rifle functioned properly before the new barrel, now it doesn't, nothing with the gas system changed.

I'm going to enlarge the port to 5/64 and shim the system to perfect the port alignment.

 

[ALMAR]

OK problem fixed, the new barrel was a little off timed with the cylinder so I enlarged the port in the cylinder slightly to make up for the mismatch and it works fine now even with reduced loads, I also made the port in the barrel to spec .078"...all is good. Seems like they drill the hole in the cylinder and barrel together to align them, so another barrel may not align with the same cylinder.

This rifle has been such a nightmare to get right, it's a good learning rifle. I may get a usgi cylinder and standard piston anyways, it's only 150 at treeline but I fear I may have the same mismatch issue because the hole in the barrel is the one that looks a little off....I may need a criterion...and the list goes on.

 

[eaglesnester]

Loose gas plug?
Does your stock piston drop with vacuum?
Is your gas plug full of carbon?
And lastly, has it previously funtioned normally with that barrel?

And I'll add that U.S. made pistons are undersize for chinese cylinders. They can work but because they are undersize the can chatter and damage chinese cylinder walls.
I've always preached that US gas pistons don't correctly fit in chinese cylinders.

I have one of the newer Norinco rifles from Marstars. I have both Sadlak pistons, grooved for 168gr bullets and up and non grooved for NATO bullets in the 147 gr range. I just finished measuring both pistons with a vernier and compared the measurements with the Chinese stock piston and they were identical. Then too I could be measuring wrong, as I am not a machinist and my measurements could be off. Both the Chinese pistons and the Sadlak pistons measured .500inch. I have noticed that the Chinese stock piston does not do the tilt test as well as the Sadlak pistons do. I attribute this to the material that the Sadlak pistons are coated with (titanium nitride and highly polished). My pistons are clean and free of carbon as is the gas cylinder.
My buddy Gunny Mork, at 29 Palms Marine Corps Air Ground Combat Center was the armorer there and he swore that gas pistons can have a huge implication on accuracy. Gunny Mork built the match rifles for the Marine Corps rifle team at the stumps.
I was getting 3 to 5 inch groups with Chinese 7.62X51 ammo with the stock Chinese gas piston. I switched to a Sadlak piston and my groups shrunk to 2- 3 inches consistently. After reloading with 168gr SMK and RE-15 and a Sage EBR stock my groups shrunk to 1-1.5MOA. Also got nearly the same results using IMR4895 and IMR4064, your results may vary.