Newby AR caliber & twist question

[joab]

I am told that 5.56 should not be fired from a .223 upper

Question is how do I tell what the AR I bought used is actually chambered for?
The lower is stamped 5.56/.223 but that does not mean much

How do I determine the twist?
Will these be marked on the barrel or upper somewhere?

 

[MMcfpd]

Most manufacturers do mark the barrel. Does your barrel have markings?

 

[joab]

If it does it's under the handguards
It's supposedly a Colt upper, but I have no idea how to verify

I bought it on a whim at a cheap enough price that it didn't matter that much

 

[DWARREN123]

It really depends on who made it. Some say not to use 5.56 in a 223 chamber and some say it okay. Call or e-mail the company and ask, they will know for sure.

 

[joab]

Got to find out the manufacturer first

Are there identifying markings somewhere

 

[Bullet]

You might find this and the links within interesting –

http://www.6mmbr.com/223Rem.html

To determine your twist rate simply take your cleaning rod and using a tight fitting patch run it through the bore from the muzzle, then start pulling it back until it is in the bore again and stop. Then take a piece of masking tape and wrap it around your cleaning rod at the muzzle and take a marker and put a dot on the tape where you can see it easily, next to the muzzle. Next start pulling your cleaning rod out of the barrel while watching for the dot. The dot will move as your cleaning rod turns. When the dot on the tape has made one revolution stop and measure from the dot back to the muzzle. This measurement will give you the distance your rifle takes to make one revolution hence one revolution in xxx inches – your twist rate.

 

[joab]

Cool I figured there was some sort of method to this, but I also figured it involved expensive equipment

 

[taliv]

yep. and you can also just peer down the bore and count the twists, then measure the length of the barrel, and do some math