PDA

View Full Version : Gas/Carbon blowing past piston


Stranger
June 06, 2007, 14:20
Okay, so how common is it for gas to escape past the piston head and drop carbon all over the end of a standard, long gas tube? After shooting quite a bit of SA at the FAL Fest I noticed that there was a lot of carbon build-up where the gas tube meets the gas tube rear support. Apparently, quite a bit of gas is making its way past the piston head and down the tube (and bypassing the holes in the tube).

Will a worn piston allow gas to escape past it more than a newer one? Would replacing the piston help with the "problem"?

BTW, there are no functioning issues with the FAL, just a lot of carbon build-up.

MACV
June 06, 2007, 14:26
The pistons get dirty. I wouldnt mess with it if its cycling good.

alphadog58
June 06, 2007, 14:27
Could be a worn tube or piston. I've noticed that SA dirtys up my rifle more than other milsurps. Had some spanish .308 (Santa Barbara?) that was real clean burning.

Larry

Stranger
June 06, 2007, 15:31
The tube is brand new. I am going to order a new SS piston just in case. The one in place right now is standard steel and had a noticable amount of rust forming on it after the Fest (where you don't have time to clean).

I think it may just be the SA. I stopped shooting my supply of Hirt and Port to focus on my more abundant stash of SA. When I get the new piston I will have to see if it makes any difference.

jerrymrc
June 06, 2007, 16:05
Originally posted by W.E.G.


Whoever said to leave the gas system "completely dry" obviously does not live in the same climate as me.

Rust sucks. Prevent it.

What is this thing you call "rust?":tongue: I know. It is the color of CE when you leave him out in the sun too long.:smile:

ce
June 06, 2007, 16:30
Let me go on, I got a blister in the sun.
Let me go on, Big Hands, you know you're the one.

Radio
June 06, 2007, 17:57
Like someone once said, unless you think Sarge is going to inspect it, why worry about it.

--Radio

Stranger
June 06, 2007, 17:57
Originally posted by W.E.G.
The M14 had the same problem. Lots of carbon.

The Mini-14 was a carbon magnet.

The Remington 7400 was a mess with carbon.

The AR-180B got all gobbed up with carbon every time I took it out.

The AK is a regular carbon fiesta.

The CETME leaves plenty of carbon in the chamber, locking area, and bolt assembly, while it blows unburned powder all through the trigger mechanism.

There has to be adequate blow-by gap on a gas piston, otherwise the thing would sieze up every time you fire it.

Swab it out with a paper towel LOOSELY (amhik) wrapped around a .30 caliber brush, and wetted with CLP, on the end of a cleaning rod.

Whoever said to leave the gas system "completely dry" obviously does not live in the same climate as me.

Rust sucks. Prevent it.

Dude, I was commenting on EXCESSIVE carbon build up. To my recollection I haven't ever had so much carbon build up on an FAL in this particular region for the number of rounds fired. Maybe its the '81 SA that I was running. The '79 stuff doesn't leave a bunch of crap in the area.

As far as cleaning out the gas system... :rolleyes: I have done this for awhile now. I never leave the gas system dry. It seems that 400 rounds of '81 over the weekend without cleaning left a lot of rust on the gas piston, and the gas piston alone. Nothing else had rust.

I was asking if carbon build up on this particular region was common. It hasn't ever been an issue in my FALs until now.

bykerhd
June 06, 2007, 22:13
Maybe you need a larger diameter gas piston. I've got them from .429 out to almost .432. The ones .430 to .4305 seem to run well in most of mine. I always look for the larger pistons. The big one is one of those DSA black ones and only runs in one rifle of mine. Too big for the rest.

owlcreekok
June 06, 2007, 23:01
SA and Port does that to my Imbel. My handloads, nope. Hirt, nope. Commercial, nope.

Wolf ?


Blech.

Wolf is teh suk.

:angel:

I ain't shot the other ones around here enough to really say. All they have had so far is my handloads. (42 grs of 4895 under a 147 FMJ lit with WLR primers) I have shot all the Wolf and Milsurp I am a going to.

Stranger
June 07, 2007, 10:02
Originally posted by W.E.G.
Are you SURE it is rust on the piston and not copper?

If the rifle is shaving copper at the gas port at all, after 400 rounds it could very well be copper you are seeing.

If it is rust, certainly nothing wrong with replacing the piston with a stainless piston. The Belgians chromed the pistons for good reason.

It was rust. There were interesting little red growths all over the narrow parts of the piston. Some got to be around 2-3 mm in diameter and a couple mm tall.

owlcreekok
June 07, 2007, 10:39
Originally posted by Stranger


It was rust. There were interesting little red growths all over the narrow parts of the piston. Some got to be around 2-3 mm in diameter and a couple mm tall.

That sounds like salsa. You ain't eatin' chips n hot sauce while cleaning your guns are ya ?

Stranger
June 07, 2007, 10:59
Originally posted by owlcreekok


That sounds like salsa. You ain't eatin' chips n hot sauce while cleaning your guns are ya ?

You got me. I also found that queso dip is a great lubricant.

AndyC
June 08, 2007, 12:05
I must have a dirty mind :D

Stranger
June 08, 2007, 12:21
Originally posted by AndyC
I must have a dirty mind :D

No dirtier than mine. I left that one wide open for abuse. :wink:

owlcreekok
June 08, 2007, 12:31
I knew this would digress, I just anticipated a different clientele.

Dirty bastages.

yuk

AndyC
June 08, 2007, 14:45
We young 'uns are just taking up the slack in the Old Guards' duties once every so often, Owl :biggrin:

owlcreekok
June 08, 2007, 15:00
I try to draw a line. THIN line, but I DO try. Ms Owl is registered on here. I dunno if she has ever even logged on except to join. I hope not.

:eek:

Stranger
June 16, 2007, 12:26
Okay, so DSA was able to get the piston delivered to me in an astounding 5 days from the initial order. I am really amazed. It seems that Dave himself intercepted and filled the order. I am well pleased with the response.

Anyway, the suspect gas piston is .03" smaller in diameter at the head than the SS one from DSA. I don't expect it to make a big difference, but you never know.

shootist87122
June 16, 2007, 12:58
Don't remove the HGs and you won't notice the buildup. The best solutions are the most simple ones. :)

FWIW, DSA pistons are slightly oversize (.432" VS .430 standard, IIRC).

owlcreekok
June 16, 2007, 21:17
Originally posted by shootist87122
Don't remove the HGs and you won't notice the buildup. The best solutions are the most simple ones. :)

FWIW, DSA pistons are slightly oversize (.432" VS .430 standard, IIRC).


Thanks for that little gem of info, Shootist. I (finally) got an inchy running today but am a little suspicious of the gas setting it is running on. My handloads generally use a 4.5 or a 5 on the metrics I got around here. This inchy wants to stutter on less than 6-6.5. I forgot which drill the port matched, but I remember thinking that it was cool beans before I pounded the block on the barrel.

Okay, tells us what gives when ya shoot it, Stranger.

Deltaten
June 17, 2007, 08:12
Stranger:

I *will* make a difference....

I have a series of pistons ranging from .429 to .4325. Swapping them out is an easy way to figger out just howbad the tube is. Tighter is better; up to the point of binding. ;)

having a group of pistons about is a comfort when one particular gun is giving fits.

AFA the carbon...prolly that batch of ammo. ALl my pistons get *some* darkness on the shaft. more with certain ammo, tho.
Cleans off easy enuff with Carb & Choke cleaner.

Best,
Paul