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About how many rounds will your rifle normally go before it won't pass the gas piston tilt test? Also when you clean the gas system do you also run patches or a brush through the D channel of the gas cylinder where the gas piston tail travels?

Just asking because my rifle seems to go only about 50 to 80 rounds before it fails the test and group size starts to increase. Is that normal?

Would appreciate any input you may have.
 

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About how many rounds will your rifle normally go before it won't pass the gas piston tilt test? Also when you clean the gas system do you also run patches or a brush through the D channel of the gas cylinder where the gas piston tail travels?

Just asking because my rifle seems to go only about 50 to 80 rounds before it fails the test and group size starts to increase. Is that normal?

Would appreciate any input you may have.
How long have you had the gun? # of rounds total through it?

When I first got my Loaded, I shot maybe 100 or so rounds before I noticed the gas piston not falling. Didn't clean it. Just went about week after week, shooting it, and wiping it down externally. Never cleaned the bore or internals, and never added grease.

I spent about 3 months doing that, and shot 1000 rounds through it (personal benchmark for a SHTF gun), and the only issues were caused by cheap, crappy mags. Somewhere along the line, I noticed it started passing the tilt test again, without ever having been cleaned.

I attribute that to the break in period.. the piston and cylinder just needed some time to wear in properly.
 

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"Death From Above"
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Shouldn't be failing that soon. When I clean the piston I use a .50 cal bore brush to swab out the cylinder. It's on a pistol cleaning rod
 

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About how many rounds will your rifle normally go before it won't pass the gas piston tilt test? Also when you clean the gas system do you also run patches or a brush through the D channel of the gas cylinder where the gas piston tail travels?

Just asking because my rifle seems to go only about 50 to 80 rounds before it fails the test and group size starts to increase. Is that normal?

Would appreciate any input you may have.
I believe alot of it has to do with the quality of your ammo. If you are using poor quality Mil Surp ammo that was dug out of a dark cave somewhere your gas system will get fouled much faster than if you were using good quality clean burning ammo. Also when you clean your gas cylinder leave it dry, do not oil the bore of the cylinder. If you do the oil will burn leaving carbon deposits and lead to premature fouling of the gas system.
 

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"Death From Above"
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Sorry for the short answer before. Another thing to watch out for is getting oil/cleaning fluids in the gas system. Supposed to run dry. I bet a dollar if oil does get in there it would get blown out on the first round but some residue may cook and stick around.
 

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Yep, that is way too few rounds for the gas system to get all bunged up. Id clean it out with some Brake-Clean (Walmart, Auto-Zone) or other brake cleaner (evaporates quickly and is not oily). Get all the carbon out that you can and put it back together. Dont oil anything..! Leave it dry...

If you are shooting really dirty ammo that could be a problem, but it would have to be some really filthy stuff (powder-wise) for it to fail that soon, unless the dimensional tolerances between the cylinder bore and piston are such that they are tight enough for just a little carbon/fouling to seize things up.
 

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Sticky Stuff

Every rifle is different. Some will run longer than others, but I have seen at least one M1A that would get the piston stuck after only about 20 to 30 rounds. It effected accuracy. The only cure was a new gas cylinder.
 

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On Ted's note you can try polishing the piston on a muslin wheel. That may help, but yeah, its possible that you need a new piston. Check the tolerances in the diagram RightHand posted. It could also be possible that when you do clean the cylinder, which does require a thorough cleaning eventually, you are not cleaning it thoroughly enough....
 

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Thanks for posting that, Righthand. A whole bunch of people really don't know how tight the fit is between the gas piston and gas cylinder when it is done correctly. It also explains why GOOD gas pistons have to be precision ground. Tip of the hat there to Sadlak on that.

The gas cylinder was meant to operate dry, but it will rust if there is no protectant on the metal surface. What I recommend is to clean the piston and cylinder with whatever brush or solvent you like, then oil the inside of the cylinder and all over the piston, THEN wipe the oil off the surface as dry as you can get it. That will leave a microscopic coating of oil to suppress rust, but won't allow foreign matter or carbon to stick.

I firmly agree with Ted that all rifles are different in the way the gas cylinder and piston "gunk up" or even how fast the piston falls. Some of the latter is if your piston and cylinder were made to maximum specs, the piston will fall slower than if they were made to minimum specs. So you have to learn what each one of your rifle's prefer.

For the best accuracy (and not just function) we cleaned some of our NM M14's cylinders and pistons a day or so before a match. Some we cleaned for the shooters the morning before each match (they knew how to hold off for the first few rounds). Other rifles went fine for as much as 400 to 600 rounds before they noticed NM accuracy just starting to slip and we cleaned them out.

Now, the rifles would still FUNCTION properly for longer than that before cleaning, but to keep the best NM accuracy, we cleaned them more often than some folks may think.

We also were using excellent quality ammo that didn't gunk up the gas cylinders and pistons. As someone mentioned, some surplus ammo is really dirty or gunky and you have to clean the cylinders and pistons sooner because of it.
 

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On Ted's note you can try polishing the piston on a muslin wheel. That may help, but yeah, its possible that you need a new piston. Check the tolerances in the diagram RightHand posted. It could also be possible that when you do clean the cylinder, which does require a thorough cleaning eventually, you are not cleaning it thoroughly enough....
I'm sure you are talking about a wheel with NO abrasive compound on it and I wanted to make that point. When pistons are polished with any sort of abrasive compound, that will change the piston diameter and you can cause a good shooting rifle to go bad when you polish a piston.
 

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I'm sure you are talking about a wheel with NO abrasive compound on it and I wanted to make that point. When pistons are polished with any sort of abrasive compound, that will change the piston diameter and you can cause a good shooting rifle to go bad when you polish a piston.
Correct, you want to polish the material, not remove it. Ive polished pistons this way and they have come out superb, but you must do it very cautiously...
 

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Further thanks to Righthand for posting that information as it leads me to adding something else.

Please note the minimum OD spec for a G.I. spec gas piston is .4970" and the maximum is .4975". Folks that entire spec is only 5 TEN THOUSANDTHS of an inch or a half of a thousandth of an inch, depending on how you want to say it. That is a tiny, Tiny, TINY tolerance for a gun part. That is also why it is expensive to manufacture a G.I. spec piston and why they cost what they do for a quality part.

I am always a good bit nervous when I get into the following because if one only uses a part of the info, it won't work correctly. It also relates fully ONLY to G.I. cylinders and pistons or at least G.I. spec. cylinders and pistons.

We separated G.I. gas pistons into a "size" for .4971", .4972", .4973", .4974" and .4975". IOW, there were five "sizes." We didn't use the minimum .4970" as so few G.I. gas pistons measured that size and we threw them in with the .4971" size. You also must remember we did not know or try to separate the G.I. gas cylinders by makers, we used all of them indiscriminately. We shot each rifle with different "sizes" of gas pistons until we found the one that worked best for accuracy in that gas cylinder in that rifle with that barrel in that gun. All testing was done in an extremely accurate and expensive test rack machine.

Usually, the rifles would shoot best with a piston somewhere between .4972" and .4974" BUT a very few shot best in either the .4971" or .4975".

We ALSO were using only three kinds of ammo: What is now Federal's Gold Medal Match, NM Lake City, and a handload we called "G4" through "G12" over the years as we slightly changed the load. We did not handload for every rifle.

There actually was a difference and sometimes a hugely dramatic difference in accuracy when we found the size piston the rifle liked best. I try to keep the different sizes of pistons in stock to use when testing NM rifles, but it is getting harder to do that as the parts dry up.

Now, please, Please, PLEASE consider this before forum members inundate Sadlak or anyone else for pistons that measure between that .4972" to .4974" sizes I mentioned. That "best spread" only works with G.I. gas cylinders and there is NO WAY to know ahead of time (before testing) what size your rifle will prefer. Further, different types of ammo and handloading procedures can throw off how valid that spread is.

If you have a Chinese or some commercially made gas cylinder, that spread may not be valid at all.

What I can say is that I've put G.I. spec pistons in all types of gas cylinders and they all worked well (if not better) for at least accuracy. So if you have one of the poorly made turned gas pistons or if it is not G.I., replacing it with a G.I. spec gas piston of either NOS G.I. manufacture or a properly new made G.I. spec commercial gas piston (like those made by Sadlak) will often if not usually help the accuracy of the rifle, but no one can say that with absolute certainty until it is tested in your rifle with your ammo.

What I do know is that I want an original or properly made G.I. spec gas piston in my rifle and any rifle I work on.
 

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Correct, you want to polish the material, not remove it. Ive polished pistons this way and they have come out superb, but you must do it very cautiously...
And it is NOT easy to do. That is why I don't recommend it for most people as it can be easy to screw up a piston. Done with extreme care and knowledge, it can be a good thing, though, on some rifles.
 

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Have to add a P.S. on choosing piston sizes. Here is what I do when choosing pistons.

If the owner of the rifle has a NM handload he really likes, I take 60 rounds of it and test his rifle with the different pistons. If not and if he is going to use Gold Medal Match, then I take three boxes (60 rounds) of that to test. If not, I prefer to test with Federal American Eagle as that is closer to NM than other commercial ammo. I can and have tested with WRA's "para military" ammo or even their NM ammo if the shooter can get that easier, though. I don't always need all 60 rounds, but that is enough for any test I've ever done.

The idea, though, is you have to have a choice of ammo you are actually going to use before you do the piston testing for accuracy. ALSO, this doesn't mean it will shoot better with everything and anything you chuck into the chamber, it can only be certain with that one type of ammo - though it usually means other ammo will shoot better in that rifle.
 

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P.P.S.

Forgot to say I do most of my general testing with Federal's American Eagle ammo as I can count on it for being really good quality from box to box and from lot to lot.
 

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And it is NOT easy to do. That is why I don't recommend it for most people as it can be easy to screw up a piston. Done with extreme care and knowledge, it can be a good thing, though, on some rifles.
If someone has a muslin wheel sitting around and uses it then they probably understand what doing it "very cautiously" means. If they dont, Im highly doubtful any one is going to buy one to polish a piston. MCORPS1

Yes, polish with extreme care if you do it. Let the piston float (spin) in your hands. Use a wood dowel in the open end of the piston...

In any event, its a piston ($60), not a bolt you are lapping into a receiver, which I would advise far more caution to than this operation, but rarely see that around these parts.....GI6
 

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The reason I mentioned extreme caution is I can't tell you how many good pistons I've seen ruined by incorrectly polishing them on polishing wheels over the years.

We used to polish pistons on a muslim wheel with no compound for Marine Corps NM M14's, but found it was best not to do that and completely dropped it in the mid 70's.

When I do my piston testing, I tell folks not to use a polishing wheel on the piston that works best for accuracy, as I don't want them messing up that outside diameter of the piston.

The solvents we have nowadays with a G.I. green all purpose brush or bronze bristle brush cleans them real nice and quick.
 

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The reason I mentioned extreme caution is I can't tell you how many good pistons I've seen ruined by incorrectly polishing them on polishing wheels over the years.

We used to polish pistons on a muslim wheel with no compound for Marine Corps NM M14's, but found it was best not to do that and completely dropped it in the mid 70's.

When I do my piston testing, I tell folks not to use a polishing wheel on the piston that works best for accuracy, as I don't want them messing up that outside diameter of the piston.

The solvents we have nowadays with a G.I. green all purpose brush or bronze bristle brush cleans them real nice and quick.
Gunny - You got the stripes. Not gunna argue. Just mentioned it because it is a method that has been and is done. I guess what I should say is if anyone out there wants to "start" playing M14 Armorer, be prepared with extra parts on hand and be ready to realize some critical learning experiences....
 

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Now, what I can not honestly tell you is the reason why polished pistons did not work as well. A lot of things we discovered were by trial and error and none of us were mechanical engineers.

What we "thought" was going on with the polished pistons was it retarded the ability of the piston to be "self cleaning." We surmised the normal precision ground surface actually was better at least for microsopically scraping powder residue and gunk off the surface.

We ran that theory past H.P. White and while they never tested it themselves, they said it sounded like a good explanation for what we found. They also mentioned that if the polished surface would have been better, it most likely would have been incorporated into the standard rifle.
 
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