put an FSB on a stripped 300 BLK barrel, gas port was off TDC

[Boolseye]

Anyone ever come across this? My first time, so I spent all my time lining the center of the gas port with the indexing lug, never bothered with a visual check! My eye told me it was a little off, but I didn't trust myself. Ended up having to re-set the FSB, take a little more material off and re-fit the taper pins, all's well now but I had a moment or two there.

Think I ought to tell the company their gas ports are off, or is that a common thing on AR barrels? I got no issue with the barrel, shoots great, port is lined up fine under the FSB, it's just not TDC. No good for lining up your reference marks.

[Green Frog]

Wait a minute... if the gas port (the actual hole in the top of the barrel) does not line up with the hole in the FSB when the FSB is aligned to TDC, how are you going to get good gas transfer for reliable operation? Have you shot this thing yet?? I'm getting ready to assemble my first 300 Blackout upper from parts that are on order now. I hope I don't have a similar problem.

Froggie

[Boolseye]

Froggie,
the hole in the FSB is quite a bit bigger than the gas port in the barrel, so it doesn't matter if the gas port is a little off top dead center, as it was with my barrel. No worries, it shoots great, plenty of gas function.

Yes, I drilled out a virgin barrel and FSB for taper pins, and I used the gas port to make my alignment marks, not realizing that it wasn't quite top dead center. It being my first time, I neglected to do a visual check–so I ended up with an FSB that was a little canted. It wasn't a big deal to correct it, since it was only off by a few thousandths.

This barrel was from a small manufacturer, and I think that the QC may be a little lax. My dad's Wilson barrel has a gas port that is exactly TDC.

[bhn22]

I have a 223 barrel from a group buy a few years back that isn't perfect either. The worst part is that the numbskull who turned it didn't leave the boss for the FSB long enough to put a full-sized FSB on. It's just long enough for a compact gas block.

[andremajic]

Have you checked the headspace? It might be possible that the barrel extension was either:
1. Slightly unscrewed or 2. screwed in tighter to adjust the headspace.

Try clamping the barrel in a vice with soft jaws and using a piece of leather or non-marring material and a pair of vice grips, attempt to unscrew/screw on the barrel extension. If it unscrews or screws on tighter, or moves at all, it might explain your problems.

Some people just press fit the barrel pin that holds the barrel extension on (aka star chamber) and it is possible for it to come unscrewed or loose, which will affect your headspace. An off center gas hole might indicate this.

Some makers (remington comes to mind) use epoxy to glue their barrels in place.

Some barrel makers will drill a dimple thru the barrel extension pin hole and then drive in the pin, but the problem is that the pin sets lower than it should.

Best fix is after headspacing, to use a center punch, followed by a flat punch to peen and displace the metal of the threads directly inside that hole and flatten and spread them out. Then, install the retaining pin. The barrel extension will NOT come unscrewed after this fix.


Andy

[akajun]

Well now that you have drilled it, I doubt the barrel company will touch it now. However If it realy bothers you or doesnt work I would use a clamp on front sight like a Yankee Hill or have it modified to be windage adjustable with set screws by White Oak Armament or John Scandale at Keystone accuracy.

[Boolseye]

Thanks for the feedback.
-BE