CMMG piston rifle

[lampworker1]

First post here,
Recently purchased carbine from CMMG with the gas piston assembly. I love the rifle and have nothing but good things to say about CMMG. I am wondering though if anyone else has any experience with the gas block coming loose during repeated firing. I went out this past week and put about 300 rounds through it, and had repeated failures. I am assuming that the heat from the exhaust is causing the gas block assembly to expand and contract in a way that caused the screws to come loose. This causes a loss in pressure and will not allow proper cycling. If anyone has any experience or any suggestions I would greatly appreciate it. I have contacted CMMG but have not been able to discuss the problem with tech support.
Thanks much

 

[taliv]

are you saying the block is obviously loose? like, rattling around or something? the screws are visibly loose or have fallen out?

 

[Coal Dragger]

A CMMG with no quality control. What a surprise. I still have not been able to even get a hold of them on the phone to talk about the pitted barrel on mine. I can only imagine the rest of my rifle is crap too.

At least the upper and lower receivers seem to be dimensionally correct, that way all the replacement parts will work.

 

[Javelin]

If this is the case I hope that CMMG corrects this quickly.

 

[lampworker1]

the screws holding the two halves of the gas block together come loose after continuous shooting. the block seems to be getting very hot. I have to let it cool in order to re-tighten the screws. I have also had problems with the large end screw loosening. When I bought the rifle it came with only one diagram of the piston assembly and it said very clearly not to over tighten the screws on the piston assembly. For $1365, I have made quite sure not to over tighten. I missed a call from CMMG today and hope to hear from them again tomorrow.

 

[Coal Dragger]

Good luck with getting them on the phone, they only have one phone line and seemingly only one guy to answer all the customer service issues.

If the screws on the gas block are giving problems you might try a high temp loc-tite on them to prevent loosening....

 

[lampworker1]

yeah, the block gets pretty hot. I don't know what temp the loctite is good to.

 

[Coal Dragger]

Red loctite is rated for pretty high temps, and the blue stuff is good up to 300F.

 

[lampworker1]

thanks for the info

 

[Coal Dragger]

Just keep in mind if you use the red loctite and ever need to get the part off you will have to apply over 300F worth of heat and some pretty serious torque to get it off.

Start with the blue, and only use red if blue will not hold!

 

[lampworker1]

talked with CMMG today, he suggested retightening a certain way and if that didnt work to use loctite. He said if that didn't work to send it back and they would look at it. I am reluctant to send it back because I am not sure when it would be returned considering how busy things have become.

 

[Iansstud]

I think they dont stamp the heads of the bolts... mine are stamped but it is not a piston... loctite should do it... use red, and it should not get hot enough to brakedown the loctite... blue will come out over time, and just use a half of a drop on each....

That is what I would do...

 

[lampworker1]

loctite purchased, starting off with blue. we will see what happens this weekend. thanks again

 

[husker]

i will be surprised if you still have a prob now