Colt m16A2 upper build

[ssgross]

I have my upper back now. Hat's off to Rich Hall, General Manager at Fulton Armory. He called me as soon as he got it in the mail...said their laser showed it was "in spec", but would test fire it to confirm if there were any issues. He reported a few days later that firing showed 7 clicks off alignment. He installed/aligned a new barrel assembly onto my upper and sent it back to me. My laser shows this one is dead on.

Most might say 7 clicks off is within the military specification, but that would be wrong. For anyone interested, the testing and inspection standards are good reads.
MIL-R-63997B (rifle)
MIL-C-71186 (carbine)

For both, barrel straighness spec is within 3 MOA of theoretical bore line, in addition to dropping a cylindrical plug through the barrel (the drop test is with a cylinder .2173 +/- .0001 inches diameter, and 6 inches long).

For the rifle, 5 clicks windage are allowable for zeroing at 100yds. For the carbine, 12 clicks (although, MIL-DTL-71186 says 10 clicks for the carbine). This is in addition to the last 10 of 15 round function firing string needing to land within an acceptable group. PDFs of the above docs can be had for free at http://everyspec.com

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[browningautorifle]

a cylinder .2173 +/- .0001 inches diameter, and 6 inches long

I had to make a couple of those as well as straightening several barrels in my time... I gave the weapons techs in Camp Gagetown NB a lesson in their own shop while doing a Galil barrel that had been out of spec for a decade or more. If a barrel isn't straight, it ain't straight. The one that has to be adjusted grossly at 100m will shoot to one side at 25 and the other side at 200. That's how you know it's out of whack. Crooked ain't straight. They have guys at Fulton to do a straightening job and then blow it out at a sale price. Unless it's bored off kilter, then it's hooped...

Off to the range now and let's see...?

[ssgross]

They have guys at Fulton to do a straightening job and then blow it out at a sale price.

Haven't seen those ever at Fulton. Full price was full price, and then some as it already had a front sight post pinned.
I certainly did my due diligence to make sure it wasn't me or my receiver before sending it back. Here is how I troubleshot...

1) I happened to have a colt factory a4 barrel assembly handy on another rifle. Put that one on this here a2 upper, and alignment was spot on. hmm.

2) next likely cause would be the front sight base installed off to the side. To check this, install the barrel, and tie a knot in a fishing line. Pass it through the peep, then tie a weight (a few washers) to the other end, stretch it over the post and down across the crown. Looked pretty dead on...and I'm confident the tolerance on this method is within 0.002 or likely a lot less after I used it align several new krag front sight bases - which all zeroed at dead on mechanical. A little math shows 1 MOA is ~0.00573 of the front sight post on the m16a2. The problem wasn't the front sight post alignment.

3) so...bent barrel? I'd like to think not. I suppose the bore could be off kilter too, but from the quality of the garand, springfield, and krag barrels I've fitted from criterion this shouldn't be the case. Don't have a cylinder for the drop test, and no lathe to for the bore axis test (Jim you are always great at reminding me I want a lathe ). My guess is that "Criterion by Fulton Armory" as these are marketed means a blank from criterion that FA finishes the contour on, installs the barrel sleeve and index pin etc. So, my thought was that the threads were cut off, or the shoulder on the sleeve was not square. Likely the latter was the cause, given the well known high quality of their work in general.

yes, off to the range. as soon as I can grab some shop time to load some ammo.

[browningautorifle]

the well known high quality of their work

I wasn't trying to suggest shabby workmanship.

[ssgross]

I wasn't trying to suggest shabby workmanship.

I know. I think I was suggesting that I doubt they would fix and recirculate a bent barrel...would instead be easier to just send it back to criterion. It doesn't matter now, whatever their practice, they did the right thing by me.