AR15 questions

[rcs9250]

I have a Colt HBAR that I want to change the handguards on. In researching the task on the web and Brownell's catalog I found something I have a question about.
I see many listings with picture of replacement barrels. They are shown as one piece. In actuality is the barrel a two piece assembly consisting of a barrel and barrel extension ?
Also, do barrels normally come with the gas hole already drilled. I can see the drilling of the hole not being to difficult with proper equipment but the deburring of the hole inside the barrel would be difficult.
Thanks,
Randy

 

[msalm]

To de-burr the hole in the bore, load a round or two and......shoot. If your just looking for a replacement hand guard, it may include a new barrel nut if a free-float model and you'll need a few tools to take the old one off and install the new.

 

[Larryh128]

Normally, all the ar barrels will have both the extension on them and the gas hole drilled. There can be a difference in the diameter of the gas hole. They range from .062-.073 as a rule. It will normally be stated what diameter gas hole is in the barrel.

 

[rcs9250]

Thanks guys. I knew about the barrel nut change. I will be needing to do that because I want a free float tube and low profile clamp type gas block.
Yeah I suppose a bullet is one way to deburr a gas hole. In the manufacturing world we would EDM the hole through. It's a more costly method but produces no burr.
Why do people buy barrel extensions ? To get one with the M4 feed ramp ?
Thanks for the help.

 

[mac86951]

M4 Feed ramp is to match the upper receiver. Barrel extensions are screwed onto the barrel similar to how a barrel on R700 is screwed into the action. Barrel extension, barrel, and bolt are what need to be head-spaced. Once that is complete the rest is a matter of holding the parts in "rough" alignment. The upper receiver holds the barrel/extension, the bolt "floats" slightly to align with the extension.

Look for the AGI videos on AR15, or other you tube videos. Sometimes it helps to see.

-Mac

 

[ridgeway]

What is the best location of gas port hole in relation to lands/grooves? Does it really matter where it ends up?

 

[Dusty Stevens]

What is the best location of gas port hole in relation to lands/grooves? Does it really matter where it ends up?

If you get it in the right spot i dont think you can control where it goes

 

[msalm]

That can only be controlled while threading the tenon for the barrel extension. I used to borescope the barrel and mark the chamber end at each groove at the distance the gas port would be drilled. I was able to time the barrel extension to one of those marks and the gas port end up in the groove. Don't bother with that anymore, and the rifles shoot every bit as accurately...IMO it doesn't matter a bit. As for the 'burr' in the port, I drill undersize, then drill with a very sharp bit and with a fair feed and if any burr pops up it is thin enough that a bronze brush takes most of it off and the bullet takes the rest...no issues. Some use a small reamer for the last few thou and that may work better. As for gas port, carbine length gas is typically .068ish, mid-length .073 if I remember correctly, and rifle length is .093". If unsure, start small, test fire, and open up a few thou at a time until a single round, magazine loaded, locks the bolt to the rear behind the bolt stop after firing. That way you know the recoil cycle is traveling fully to the rear.