Gas block question.

[SeanF]

I'm buying a gas block and I need to know what size to get. I have a 20' heavy barrel. What one do I buy?

[xounlistedxox]

Which company is your upper from? A lot of stndard type barrels are .750, but if you have a bull barrel, or something in a caliber other than 5.56 it might be totally different

[SeanF]

I'm thinking its standard its 5.56 I thought it was larger because it was a heavy barrel but I was wrong.

[xounlistedxox]

Is it a heavy barrel, or a bull barrel? Heavy barrely are thick under the handguard, but are reduced size from the gas block forward. Bull barrels are thick all the way to the end

[NavDoc]

Popular gas block inside diameters...

Pencil/LW: 0.625"
Standard/HBAR: 0.750"
Varmint/Bull: 0.936"

[elrcastor]

get a micrometer and measure it

[ar15barrels]

Popular gas block inside diameters...

Pencil/LW: 0.625"
Standard/HBAR: 0.750"
Varmint/Bull: 0.936"

Armalite AR-10T: 0.875"
Alexander Arms: 0.907"

[FMJBT]

get a micrometer and measure it

+1

Even a cheap $20.00 dial indicator from Harbor Freight will measure accurately enough for this.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=66541

[ar15barrels]

Even a cheap $20.00 dial indicator from Harbor Freight will measure accurately enough for this.

How would you use a dial indicator to measure diameter?

The dial calipers you linked would work fine, but using a dial indicator would not be optimum.

[FMJBT]

How would you use a dial indicator to measure diameter?

The dial calipers you linked would work fine, but using a dial indicator would not be optimum.

Brain-farted that one. It happens sometimes.

[1988]

Measure the barrel yourself to make sure its correct size. Most barrels are made to standard sizes, but custom made barrel is not uncommon in the AR world.