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Posted: 6/27/2005 5:20:45 PM EDT
| Has anyone ever had the gas port drilled to small in a factory barrel ? |
| there is really no such thing as too small or too large as every factory uses a different size for their barrels. the sizes are in a range depending on the configuration of the barrel. but yes, I have seen factory barrels whose gas ports were smaller than they needed to be to function reliably. most recently I found a BFI barrel (20" A2) with a gas port that was only partly drilled. |
On a 20" barrel, if it is .625" under the FSB, then the gas port needs to be between .086" and .093". If it is .750", then it needs to be between .093" and .096". On a 24" barrel, the only spec I have is .089". |
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I saw that 0.089" spec as well, but I think that is for a 0.825" barrel (bull barrel?) I just want the info first because I plan to check it this weekend and I'm sure everyone is going on vacation or something and won't get back to me in time. I have a 24" H-Bar, with the barrel being 0.75" under the FSB. My gas port should measure 0.093"-0.096", correct? It seems like a lot of the specific specifications are a mystery to anyone other than a double super secret squirrel official armorer. I have a #42 drill bit, 0.0935" but I don't have a #41 drill bit (0.096"). I can at least use that to check the size of the hole more accurately than a caliper. |
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11.5" barrel, .625: dia., 3.850" from muzzle; Port sizes from .081" to .089" 11.5" barrel, .750" dia., 3.850" from muzzle Port sizes from .086" to .094" 14" barrel, .625" dia., 8.375" from muzzle; Port sizes from .063" to .078" 14" barrel, .750 dia., 8.375" from muzzle; Port sizes from .070" to .086" 16" barrel, .625" dia., 8.375" from muzzle; Port sizes from .063" to 078" 16" barrel, .750" dia., 8.375" from muzzle; Port sizes from .070" to .086" 20" barrel, .625" dia., 8.375" from muzzle; Port sizes from .086" to .093" 20" barrel, .750" dia., 6.875" from muzzle; Port sizes from .093" to .096" 24" barrel, .825" dia., Port size .089" 20" 6.25" .093" 16" 8.50" .063" 14.5" 6.75" .067" 11.5" 3.875" .076" 10.5" ? .089" |
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Tweak: Thanks. I'll just dip the #42 drill bit (0.09375") into the gas port and if it goes in, I'll leave it as-is. With the recent constant screw-ups with my Bushmaster orders, I think they may have hastily slapped together the "pre-ban" 24" NM H-bar when I ordered it a week after the AWB expired - meaning they probably didn't check the gas port size. Should the FSB tower have comparable dimensions for all barrel configurations? I don't have a spare crush washer otherwise I'd take off the FS (A2 birdcage). |
Yeah, you were helping me troubleshoot my rifle and suggested I check the gas port size. I think I eliminated all the other things (gas key, key screws, gas rings, action spring) and I'm left with checking the gas port size. |
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