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Posted: 12/16/2005 11:04:44 AM EDT
What could be causing a massive amount of gas blowby in my AR Carbine?
After firing as little as 1 30 round mag, the firing pin, hammer, and inside of the upper are gray from the gases. The Carbine has a Colt carrier, DPMS bolt, H2 buffer, and Wolff extra power buffer spring.
It has been 100% reliable so far, after over 500 rounds, but the filth in the upper has me wondering.
I have another Carbine, and it does not have these issues.
My gut feeling is that there is an issue with the bolt, since that is where the gasses do their thing. The bolt is new, and the rings are new as well, with no aligned gaps. Is there something with the combination of parts I used, which could be causing blowby?
Link Posted: 12/16/2005 12:34:58 PM EDT
Nope, really just normal fouling from the gas system.

Most of the gas from the gas chamber of the carrier gets blown out threw the two exshaust ports as te bolt unlocks (two holes in the carrier), but some of the gas will leak out threw the back of the carrier/bolt, and even some more will blow back threw the key one the gas tube has cleared. Also, since the chamber is still under pressure when the spent case is pulled, add that gas in the action during cycle.

Bottom line is to just keep the upper bearing areas lube with CLP and let the CLP deal with the fouling to keep it solvent/trouble free.
Link Posted: 12/17/2005 12:50:42 PM EDT
Just for giggles, I took a bolt from my parts pile(Colt), and swapped it in place of the DPMS bolt. After firing 120 rounds, there was just a hint of soot on the firing pin, and hammer. The rifle ejected the brass with more authority also. I am going to check out the DPMS bolt with a micrometer, and compare measurements with the Colt bolt. I would like to keep the Colt bolt in the rifle, but it has around 10k rounds through it.
Link Posted: 12/17/2005 8:07:37 PM EDT
Link Posted: 12/18/2005 8:58:08 AM EDT
Tweak:
I did a side by side comparison of the bolts, and the DPMS bolt has issues. The tail on it has a step where the .250 O.D. transitions into the radius. The step then has a slight angle on it, before the radius begins. Its not a smooth transition like on the Colt bolt. The Colt has no steps or angles.
Pretty shitty workmanship on the DPMS bolt. I will not be buying anymore of their junk in the future.
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