If the answer to my question is obvious, please excuse me. I'm only trying to verify what I think I know.

I want to replace a bbl on an upper and want to make sure I end up with chrome in all the right places.

TIA.

Yes.

I was just going to ask if Colt 20" uppers have M4 feed ramp chambers- course this would make me an idiot- trying to figure out why my Colt upper with M4 barrel had the feed ramp cuts in the chamber.

Now I know and I feel stupid.
Ha!,
Creeper

Correct me if I'm wrong but wouldn't a chrome lined barrel imply the chamber is lined also. It seems to me I have heard of a chamber being chromed without the bore but never the converse.

True, false, medication wearing off?

Generally true, but not necessarily so.

Colt has done everything under the sun with barrels and chambers and probably invented some new ones, just to be 'different'.

Also, someone may have rechambered a chrome lined barrel either by way of a caliber change on the cheap, or to make use of a super-cheap take-off military surplus barrel which had short headspace.

I've never personally seen a rifle with a chrome lined bore and unlined chamber, but that doesn't meant there couldn't be one out there, somewhere.

The chamber is the barrel extension which is screwed into the rear of the barrel.

That said, you will recieve a barrel extension with any new barrel you buy.  It will be preinstalled just like your front sight tower/gasblock.  But it is not technically part of the barrel and it can be removed and a new barrel extension added.  You could techically take a chrome lined barrel/barrel extension and swap with an unlined barrel/extension and have one with a lined chamber and unlined barrel and the other with a lined barrel and unlined chamber.  Why anyone would do this is beyond my imagination.

[lolabove]

[url=http://www.boomershoot.org/general/GunDict.htm]Chamber[/url]

While the barrel extension plays a part in headspace the chamber is considered to be, "That portion at the rear of the barrel of any gun that is enlarged to accept the loaded cartridge and support it during firing."

"Firearms Encylopedia" George c. Nonte, 1975.

Odds are it won't line up with the front sight post when installed. During assembly the extensions are screwed onto the barrels, the alignment pin pressed into them and then the FSB is mounted on the barrel. The mounting jig indexes the FSB to the alignment pin in the barrel extension. If you install a new barrel extension odds are extremely great that when tightened it will not be aligned with the FSB as the breech threads on the barrels are not timed.



Barrel extensions are not chromed, they are [url=http://www.britannica.com/ebc/article?eu=385098]carburized[/url] precision ground [url=http://www.suppliersonline.com/propertypages/8620.asp]SAE 8620[/url] steel. They do have a shiny appearance before parking tho. The chrome plating fade out is usually within a 1/4" of the mouth of the chamber.

[linx]

Troy,

How is calling the lowered feed ramps "M4 ramps" incorrect?

Weren't the very first M4 carbines built from standard A2 uppers without the elongated ramp cuts?

Considering that the barrel extensions and uppers with the lowered ramps are both marked "4" I think I'll stick with calling them M4 ramps. [:)]