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10/20/2017 1:01:18 AM
9/22/2017 12:11:25 AM
Posted: 9/7/2005 6:37:45 PM EDT
I'm in the process of barreling my first upper, and I'm unable to find the right gas block. A quick search didn't help, either.

I'm using a like-new 20" Colt HBAR that's .729" diameter at the gas block and a Colt free-float tube off an Elite rifle. I'd like a steel gas block, but all the gas blocks I found at Brownells and Midway are .750" diameter--nothing .729".

Can anyone point out a steel .729" gas block, preferably with either a fold-down rear sight or a single rail so I could attach a front sight?

And, what's better--clamp on or set screws? Clamp-on looks easier to install, but...?

Thanks for advice!

Link Posted: 9/7/2005 7:20:44 PM EDT
What type of measuring device did you use to measure the diameter at 0.729 inches?
Link Posted: 9/7/2005 8:26:48 PM EDT
Something is very wrong here.
The gas block seat (that's the part of the barrel where the gas block fits) will be VERY close to 0.750".
Usually around 0.7496" to 0.7498" in diameter.
This is how I make them on the barrels I build unless the barrel is being made to fit a specific gas block, then they MAY be up to 0.752"

The 0.729" does sound right for the area of the barrel just in front of the gas block though, 0.730" is typical.

There are other standard sizes as well: 0.937" and 0.625"
I heard that one maker uses 0.709" or 0.790" for some odd reason, probably so that you HAVE to buy parts from them...

Randall Rausch
www.ar15barrels.com
Link Posted: 9/8/2005 11:30:06 AM EDT
Maybe I measured in the wrong place? I measured right next to the gas hole. There was a step up, with a slightly larger diameter, just to the rear of the gas hole. If that's where I should have measured, that would probably be close to .750". I'll check when I get home.

Can anyone confirm the correct location to measure?

I appreciate the help.
Link Posted: 9/8/2005 12:19:04 PM EDT
Here is a quick sketch:



Make any sense?

Randall Rausch
www.ar15barrels.com
Link Posted: 9/8/2005 12:25:06 PM EDT
Randall,

That's a great pic and leaves no room for misunderstanding. I think I measured right where you have the arrow showing .7500", and not over the gas hole itself. I'll go re-measure everything tonight and post the results. Hopefully it's my mistake and not a problem with my barrel.

Thanks for the crystal-clear pic!
Link Posted: 9/8/2005 7:21:34 PM EDT
Uh, I re-measured and I am a moron. It was .750. I must have misread .749 or something.

Thanks for the help!

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