
Originally Posted by
TinyCrumb
I'm not meaning to step on anyone's toes here, but I disagree with a lot of the information in this thread.
The gas on an 11.5 should be smaller than a 10.3, not larger. .070 is Crane spec for 5.56 Nato out of 10.3" barrels. .063 is stock 14.5" Colt Carbine. The 11.5 has more dwell time than the 10.3 and less than the 14.5".
If the barrel had been chopped to 10.3" with no gas port work, you would have seen more drastic short stroking. Since you only cut to 11.5, you didn't reduce the dwell time as drastic as 10.3" would have, but enough that your rifle was functioning *just* on the verge of reliability (i.e., rifle would cycle but would not lock back on last round).
My opinion is you went about this all wrong. First off, I would have got the correct gas port spec. Secondly, I would be tuning the rifle for a carbine or H buffer, not *starting* with an H3.
Something around .067/.068 would have given you a properly gassed rifle with a carbine or H buffer.
You now have a severely overgassed rifle, and even though you're able to use an H3 to tame it down, you're at the end of your buffer options already and you'll experience faster port erosion and parts wear than necessary.
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The 10.3" barrel ends pretty quickly right after the gas port, which means the system only stays pressurized for a very short amount of time. Because of this, the gas port needs to be "enlarged" to insure there's still enough pressure in that short amount of time to cycle the action. The longer you increase the barrel after the gas port, the longer the system remains under pressure and the smaller port is proper for proper functioning. A 14.5"/16" factory Colt for instance will have a port of around .063 from the factory.
I really don't understand the advice in here saying an 11.5" should have a larger port than 10.3".
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