Tilt test fails - gas system

M

Martin248

CGN frequent flyer
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Piston falls out properly if I hold the muzzle up, but if I hold it with the muzzle down piston stays stuck fully extended. If I tap it slightly it falls back smoothly--it seems that the problem is only at the very end of the piston's travel. It moves smoothly through the rest. It's like it sticks to something when it's all the way out.

I took it out and tried cleaning it, and cleaned the gas system to the best of my ability (hard to get in there, I don't have the right tool). It doesn't seem to be causing any problems, I put about 150 rounds through it on the weekend and it functioned just fine. This is only something I noticed when I had it apart for cleaning afterwards.

Not sure what's causing this. Any ideas?
 
Passes the tilt test fine when the operating rod is installed, the weight of the oprod and bolt is enough to push the piston back in, so I guess I won't worry about it.

I did notice that my operating rod guide is loose as all heck. I guess I should probably tighten that up?
 
You probably just have cleaning gunk in there that seeped down from the gas port. Open that badboy up and sponge it out

sponge it

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Sounds like a good fitting piston to me. I dont think this is a problem at all. The sticking of the piston to the rear is most likely just a vacume effect that wont affect your rifle from functioning properly. If you think about it, theres a giant rod with a spring pushing up against the piston to return it to where it should be.

In terms of tweeking some accuracy out of your rifle you want to ensure a consistent cycling function in this area. I'd be concerned if the op rod was misaligned such that the piston is not centered on the rod's face, if the gas piston was too small/loose for the gas cylinder (not your case), or if there's considerable binding in the op rod spring (simple addition of a spring guide rod to address this). None of these are neccessary fixes to make your rifle function properly, but can help to slightly reduce your grouping size.

Just make sure that you keep the piston clean, dry and free of oil. If you oil your piston, the carbon from the hot gas entering the system will gunk up the piston faster and may also result in faster accumulation of rust in the cylinder. I usually clean out the gas cylinder and piston with soapy water and a soft non-metal bristle brush. In the rare event of rust, brake cleaner does the job perfectly.
 
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