So this is an 11.5" barrel(according to the invoice from where I bought it).  Okay, where exactly is the 11.5" measured from?



This is the same barrel with a 5.5" (actually about 5.6") flash supressor I am about to pin and weld on.  I just want to make sure I am meeting the 16" requirement


Thanks

ETA, yes...I know....Why are you doing that?!?!  your loosing so much power/accuracy whatever.  I have other rifles for that.  This is just for fun.

ETAA, Could not find a 11.5 with the welded "holes" FS and a chrome lined barrel.  So I ordered an 11.5" chrome lined and doing it myself.

From the breach face wich is further in than the extension to the end of the muzzle threads or muzzle.

"Why be silent and be thought an idiot, when you can open your mouth and remove all doubt?" Having said that, I'll throw out my uneducated opinion.

I have no doubt that with the pinned/welded 5.5" F/H, you meet the 16" requirement. It would appear that your bare barrel is truly a 12" barrel, but is being called an 11.5" barrel because whatever length F/H or comp you attach is going to overlap (or use up) 0.5".
The mfr wouldn't want you to think you could add a 4.5"  F/H to their 11.5" barrel and come up with a legal 16".

Quoted: Barrels are measured from a closed bolt. Install a bolt and put it in the locked position. Take a dowel rod or cleaning rod and insert from the muzzle end. Mark rod after it touches the bolt and you have your lenght.

+1


that and where the muzzle device overlaps the threads it doesnt count


ex. if the threads are 1/2" + the 5.5" fh its still only 5.5 mounted

Quoted: Barrels are measured from a closed bolt. Install a bolt and put it in the locked position. Take a dowel rod or cleaning rod and insert from the muzzle end. Mark rod after it touches the bolt and you have your lenght.

Correct, and well spoken so that others may understand.

Quoted: Barrels are measured from a closed bolt. Install a bolt and put it in the locked position. Take a dowel rod or cleaning rod and insert from the muzzle end. Mark rod after it touches the bolt and you have your lenght.

OK, let me try to explain what I found out the other day.  I took a new 14.5 inch barrel without a f/h on it, installed a bolt and inserted a rod down the barrel.  I marked and measured with a measuring tape.  I (burned) one inch and started measuring the rod from 2 inches.  That way you don’t get any error from the very end of the tape.  The actual length came out 1/8 inch past 14.5 inches.  On the bolt, I measured the distance from the face of the lugs on the bolt to the face of the recesses area that the brass sets in and it is 1/8th inch.  What I am saying here is that when you measure with a rod down the barrel you are including the 1/8th inch length that is recessed into the face of the bolt.  Because I know that the barrel is new and is a 14.5 inch m4 barrel, I am confident that the measurement should start at the face of the lugs.  Just subtract 1/8 inch from the measurement you mark on the rod.   Ill add a picture.  

here you can see the recesses area.

Quoted: Barrels are measured from a closed bolt. Install a bolt and put it in the locked position. Take a dowel rod or cleaning rod and insert from the muzzle end. Mark rod after it touches the bolt and you have your lenght.

COOL!  Thanks!  And thanks to all of ya.

Upper and bolt assembly are coming from the big brown happy truck tomorrow.  Hopefully I can get drilled/pinned/welded tonight so I can put her all together and post pics Tuesday night.

Quoted: Barrels are measured from a closed bolt. Install a bolt and put it in the locked position. Take a dowel rod or cleaning rod and insert from the muzzle end. Mark rod after it touches the bolt and you have your lenght.

yup.

Bummer.  FS on is a little over 16.5"