another gas block question..


February 8, 2012, 05:18 AM
am putting a low pro gas block on my at 15 and I was wonderin I have to try and line up the hole by measuring or does the gas tube go all the way against the bolt? I guess I'm just asking for some insight from someone with more experience than me.. I wish I wouldn't have been so antsy taking it apart!

Thanks jakerr15

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February 8, 2012, 07:53 AM
A lot depends on what GB you are using. Most of the time you install the GB against the shoulder on the barrel. If you are using a floated hand guard then you need to compensate for no end cap.

You'll need a dial caliper, $20- off evil bay, the do some checks. The gas hole in the GB is larger than the gas hole in the barrel so you have some fudge room. You well have .004-.006 to play with.

February 8, 2012, 12:14 PM
Bot does the gas tube have to be almost flush wither the bolt?

February 8, 2012, 08:30 PM
The gas tube does not go flush with the bolt, but feeds into the top of the bolt. The propper length gas tube will ensure it goes into the bolt. The important thing is that the hole in the barrel and the hole in the gas block line up properly to allow the gasses to flow without restriction. If the two holes do not line up you could end up with the action not cycling properly and see short stroking issues. Measuring may help verify. Also make sure it is not severely twisted side to side. Some installers also chamfer the holes if there are alignment issues.

February 9, 2012, 12:10 AM
Chamfer is what now?

February 9, 2012, 02:18 AM
Is there a set / known distance that the gas tube hasto be away from the bolt?

February 9, 2012, 04:25 PM
Chamfer is an inside taper, like countersinking for a flathead bolt.

the gas tube goes INTO the Bolt Carrier Key- the part on the top of the Bolt carrier that sticks up and forward on the top front of the BC.

If your's seems to be short, you may be trying to use a carbine length on a Mid gas barrel, or a Mid on a rifle length.

February 9, 2012, 04:31 PM
about 30 seconds into this video shows it in cutaway:

February 9, 2012, 05:36 PM
I guess what I'm asking is if I line upbthe holes with the gas block and barrel will the gastube be where it needs to be? I'm using a low profile gas boycott with a carbine lenght gas tube and a midlength free float tube

February 9, 2012, 05:46 PM
Yes, if the Gas Block is correctly mounted to the barrel, and the gas tube is the right length for the barrel (carbine barrel, carbine gas tube), the right amount of gas tube should protrude into the upper receiver.

DO make sure that the gas tube is far enough into the gas block for the gas block (gas tube) pin to engage it, and make sure the tube is right sdie up before you pin.

I've done the first wrong, and a friend screwed up the second.

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