I have a Springfield armory m1a loaded it has a sadlack gas piston and guide rod. It doesn’t cycle the next round.  I am using brass ammo not steel case and it passes the tip test I was wondering if anyone had any ideas on how to get It to work again.

It also has powder marks right above the small hole in the gas piston I would be happy to message anyone the pics of that as for some reason I can’t post pictures.

Did it run prior to switching parts?
Does it have an adjustable gas plug, is the plug tight?
Have you checked the gas cylinder alignment with the gas port in the barrel? Use a small Allen wrench and push it up into the barrel. See if you can see the wrench in the barrel.
Does the gas piston fall freely, did you "lube" the piston?
If you greased or oiled the piston remove the grease or oil, it's meant to be dry...

Does the op rod move freely...

Remove the spring to test the op rod

**** make sure it's unloaded before looking in the barrel for alignment (Just sayin')

Make sure your gas spindle is in the right orientation, and you didn’t accidentally shut off the gas when you changed pistons.

try this

The gas spindle is in the correct position.  The gas piston is not adjustable.  The gun passes the tip test it did do this with the original parts.  The op rod does travel Feely. I can’t post images otherwise I would post of a pic of the gas piston because to me it looks like it’s not in alignment with the hole in the barrel.

The gas cylinder is the only part which would potentially not be in alignment with the barrel's gas port. Usually that's not the problem however.

Ensure the gas plug is tight. Use the closed end of a wrench to tighten it. The plug being loose is the most common cause.

It's perfectly normal to see carbon fouling forward of the hole in the top of the piston. It starts to move rearward while gas is still coming through the gas port.

Try these tests...
(after ensuring the rifle is unloaded of course)

Remove the stock and point the muzzle up.
(Set the receiver heel on a table or something.) Sharply retract the op rod. The gas piston should extend downward due to gravity. It should take 1.5 or 2 seconds to bottom out in its extended position.

Now lock the bolt open. Use your thumb to sharply push the piston forward all the way. You should feel/hear some compression.

If it fails these tests there is something wrong in the gas cylinder assembly.

Chinese gas cylinders and pistons are different diameters than U.S. cylinders and pistons, so one can go out of tolerance by mixing up their parts. Chinese gas cylinders & their plugs are metric threaded. So is the gas cylinder lock that threads onto the barrel.

I wouldn't expect to find Chinese gas cylinder parts on an M1A, but if you purchase a used rifle, it's possible.

If a Chinese gas cylinder, piston, and plug were all swapped over together, it shouldn't cause an issue.

You can check your gas port alignment with an Allen wrench, as mentioned above, or remove your gas cylinder and mic the location of the port in comparison with the barrel. Sometimes people add shims under the stock ferrule so investigate that also.

Take the piston out and check the gas port’s alignment with the barrel with an allen key through the bleed hole in the bottom of the cylinder. Looking down the muzzle you should see the allen key sticking into the barrel. If it is not you will either have to tighten the cylinder lock ring till it does or shim the stock ferrule.  till the cylinder lines up. Do not over tighten anything. Keep in mind your piston has a flat that orients it correctly in the gas cylinder too. If the tail of the piston cannot move in and out of the back of the cylinder freely the piston is likely out of spec. You can check this with the action locked open or with the op rod removed.

OP:  
Has the rifle ever worked for you?  
So it not working now that you replaced something?

Which Sadlak gas piston?

The guide rod may have to be modified to work properly in your rifle.

Can you swap magazines just as easily as before? Or do they stick and require you wrestle with them in or out?

Did you replace the recoil spring with a new one? I ended up having to remove 1.25" from a new spring to get reliable function.

Simply run the action by hand paying attention to any resistance you encounter. Make sure the bolt locks back on an empty magazine.

Who's magazines are you using? A lot of junk magazines are on the market. Use current manufacturer US Gi mags.