I have a can on a 14.5" gas piston m4. It blows tons of gas back in my face. I was told by someone that changing the buffer or adding a tubb carrier weight would keep the bolt locked a little longer to help reduce the amount of gas.
Any suggnestions. Thanks in advance.
I have never heard that fix before so I don’t know. But a gas buster charging handle should help. FMJs-of-Freedom
What kind of can?
YHM - 7.62
Wow. That is strange. I’d have guessed that a 7.62 can would yield a lot lower amount of face gas.
I’d run a heavier buffer if the set up will work with one. Theoretically, if the bolt were slower to unlock, you’d expect the gun to force more gas through the can. 
Gasbuster CH have a tendency to break. If you are going to spend the money on a new charging handle, may I suggest going with a BCM Gunfighter Charging Handle. If you need it to be a “gas buster”, 03DESIGNGROUP.com has a way to modify your charging handle here.
S/F
Dozer
will a gas buster make a diff even on a gas piston?
In my experience piston uppers gas the shooter as much if not more than D.I. uppers. A Gasbuster helps a little.
I will try the silicone trick.
But that is impossible! Gas piston guns are SO much better than DI guns. They even wake up at night and clean themselves. You NEVER have to clean a piston gun at all! They don’t get dirty at the range, you can shoot them under water, they are way more accurate, the shooter gets NO gas when running a suppressor, they are quieter with a suppressor than a DI gun and they make the user a total stud in the bedroom!
All the cool kids are getting 'em too.
Sorry, I couldn’t help myself. 
I very much agree that a GB CH will help a bit. It won’t eliminate 100% of the gas but it makes a lot of difference in my experience. Also, some guys really like running their guns very wet (oily). Don’t. Play with dry lubes if you must.
Mark