is this normal (gas tube leakage)

[30 cal slut]

looking from the top down:

this is a colt mtc m4 that i had a gunsmith modify.

the factory gas tube and front sight base were replaced with bcm components (long story, i removed and lost the original parts). the fsb is cut down.

i put about 70 rounds of M855 through this yesterday. rifle functioned perfectly.

however, i noticed some leakage where the gas tube meets the fsb. it's hard to tell, but there is a ring of carbon around the gas tube at the top. you can see some of the residue on the surefire g2 to the right.

didn't bring a chrony with me to measure bullet velocity.

i've done a search on some other forums re: ar15 gas tube leakage. some say it's normal, others say that Colts (although modified) shouldn't be doing this.

http://i44.photobucket.com/albums/f15/30calslut/GasTube.jpg

[Quib]

From my experience, some gas leakage at the FSB is normal. It should be self limiting and eventually seal it self up.

ETA:

http://img.photobucket.com/albums/v489/Metroliner/FSBLeakage.jpg

[Blankwaffe]

+1 Quib...
In my experience I'd also say its pretty common to see carbon residue at the gas tube and FSB.As mentioned after a few hundred rounds the carbon will build up at the juction and the amount of residue seen will decrease,but it will still show signs of some blow by as its not a pressed fit or technically sealed.
Also common to see some carbon fouling at or around/behind the delta ring due to the blowby of gases at the gas tube and carrier key mating being expelled out the clover leaf in the receiver.
As long as the weapon functions 100% I would not worry about it.

[30 cal slut]

much obliged. i guess that kind of leakage is easier to notice on light-colored rifle.

[Mac5.56]

Interesting info to know. I had this a little a bit at first too.

[Detmongo]

as i understand it if it is a new barrel it will seal itself from some carbon buildup over time. i have a training upper that does this with about 3000 rds thru it so far. other than a wipe down of the carbon off my white light, i've had no malfunctions with this upper.

[Frens]

...it will seal itself from some carbon buildup over time.

correct ;)

if the rifle/carbine cycle and it's reliable dont worry about it

[Detmongo]

fren,
thank you that's good to know. the gun runs fine so i'm not to worried. i built this upper for teaching so it won't see the street, but i need it to run properly which it does.