14.5" Colt R0723 barrel in H&R C7 upper. Barrel extension has a fairly normal fit into receiver. No mallet needed. Not sloppy. Geissele reaction rod. Barrel nut torqued to 34ish ftlbs.

Currently right 4 clicks (as I see is common with reaction rods).

Aside from leaving well enough alone, which I should do, what could I do to make this really centered? The receiver is a blem and I consider it sacrificial. I have a lot of spare time and my range is close.

Should I peen the right side? Should I do the thin strip of soda can aluminum in the receiver extension notch (flattened into a U shape). Should I shim right side?

First upper I built I had to go hard left on the rear sight and that really bothered me. I disassembled it and got the lapping tool from Brownells or Midway and lapped the front facing part of the threaded extension. And then I bedded the barrel. It was perfectly centered after that. Ever since that first upper build I have built 9 or 10 more and always lapped and bedded and they were all perfectly centered. Some people say it doesn't matter, but I can't help but think it would negatively effect zero at different ranges.

I had heard about lapping the receiver but never looked into it. That's a cool tool. I need that.

Ordered.

Does that reaction rod have a "fin" the locks into the charging handle channel?

No. It has 8 positions (45 degrees apart) which makes it useful to rotate the upper assembly around to look at everything while working on it. Geissele make a "Super" version which has adjustable brass tabs to engage the upper if you have a stuck barrel nut or have to torque up near 80.

Do you happen to have an upper receiver clamshell block?  When you tighten the barrel nut with only the barrel being held, the index pin will be pressed against the right side of the slot (as viewed from behind the receiver) whereas if you clamp the receiver, the pin will favor the left side of the slot.  It might get you a thou or two, and you can always file a hair off the appropriate side to get a little more if needed.  Lapping the receiver face should also be considered.

It is also possible that they just plain fubar'd the FSB when they pinned it, and there is only so much you can get back before you start affecting bolt/feed ramp alignment.

Thank you.

Of course, you know that it could be that the barrel is perfectly aligned and the barrel just shoots an inch to the left . . .

And then there is that

If it means that much to you, you could build a fixture that clamps your upper receiver and barrel into perfect alignment. I envision something on a 1/4" steel plate at a minimum with fine threaded adjustment screws that thread through brackets welded 90 degrees to the base plate and hold or push against the FSB. A laser centered at the receiver end could shoot a beam through the rear sight aperture and just adjust until the front sight post is perfectly aligned. Then tighten the barrel nut.

Because of the precision involved, I could probably build such a rig for maybe $600-800. When it's done, as has been pointed out, it will pretty much absolutely not shoot dead center.

4 clicks seems like a really reasonable adjustment. I can't think of a single rifle I own, built or purchased, that didn't require some windage to zero.

As mentioned, your barrel/FSB may or may not be in perfect alignment now as it is.


Here's one of my perfectly aligned examples.




And here's my windage after zeroing.




I'm more than tempted to take that one apart and try the lapping tool since so many have made the claim that it brought their windage adjustment to near center. However, at the same time I feel like I'd be chasing unicorns since the dead centered FSB alignment indicates that the receiver face would have to be even, at least in the horizontal plane.


With that said, we can't rule out that your use a finless Reaction Rod may have damaged the indexing pin notch on your upper receiver by forcing the upper against the indexing pin while tightening the barrel nut. Yes, damage can easily be done at only 30 Foot Pounds using the Reaction Rod.

Here's an example of a Brownells A1 upper I messed up. Left side damage to the indexing pin notch was caused by using clamshell upper receiver vise blocks and forgetting to lube the forward/FSB facing side of the barrel extension flange (so it twisted with the barrel nut). I got up to around 70 Foot Pounds before realizing my mistake. I knew something was off because the barrel nut alignment was not advancing as I got closer towards the max in torque. I went to loosen the nut and it popped loose with a loud squeak! I instantly knew that I had forgotten to lube the forward facing side of the barrel extension flange.

Right side damage to the indexing pin notch was caused by using the Geissele Reaction Rod at only 30 foot pounds of torque. I switched from the clamshells to the Reaction Rod to bias the indexing pin to the right side of the notch because I had damaged the left side of the notch using the clamshells... It didn't work out as all I managed to do was damage both sides of the indexing pin notch and still couldn't get the FSB centered. But, I got a good example to show off so people can see what can happen.




Clam Shell damage at the left side of the notch.




Reaction Rod damage at the right side of the notch.

Every time you post those same pictures I am reminded of that scene out of the movie Basic Instinct when Sharon Stone raises her shirt and shows her tits to Michael Douglas, .............he stares at them a bit and then states "Ive seen them before" !

Those are great tits, I mean pictures.

Well, I gave it my best shot with those pics to make sure they were clear. And believe it or not, I've never actually seen that movie, lol.

Thanks for the complements on the pics! And Happy St. Patrick's Day!


And in before any warnings about comments not being fit for tech.

The really, really obsessive way to torque barrel nuts is to have two vises lined up, with the receiver in clam shell and the barrel held in barrel blocks, then the only thing that can move is the barrel nut.

A reaction rod-like device with the anti-rotation bar on top is almost as good.

Correct, and as shown below I've found an easier way to accomplish the same thing for anyone that really wants to make sure that the barrel and receiver don't move in relation to each other.


Only addendum to make about the below video of OTDR showcasing my barrel installation/removal method is to use the 2UniqueLLC barreling spud in place of the MI-URR. The 2UniqueLLC barreling spud fits the barrel extension with very minimal to no play, whereas the MI-URR fits with a bit of play in the barrel extension. Also, be sure to tape the sides of the "fin" so that there is no play in the tool to the upper fit and then both parts (upper and barrel) will be as solidly together as they can be while you torque on the barrel nut.



I will note here that it's best to check your sight alignment with an FSB alignment gauge prior to applying any torque to the barrel nut. Depending on if the FSB alignment is only off a very slight amount one way or the other, it can be biased closer to center depending on if you use a "fin" topped reaction rod (for biasing the FSB to the right) or upper receiver vise blocks (for biasing the FSB to the left).


OTDR has a video for putting together your own FSB alignment gauge too.

Update:

Disassembled the upper. There is a faint impression from the barrel extension pin on both sides of the upper receiver, R>L. No where near as much as what is shown above. This upper was assembled with Geissele reaction rod.

Also, there is slight play in the notch. When I rotate the upper receiver to the right (creating space to R of pin), the ears of the front sight base line up with the ears of the carry handle perfectly. When I rotate the upper receiver left things are slightly askew. When I reassemble I am considering adding a shim to the right side of the pin recess. Also going to (ZOMG change a second variable at the same time) lap the upper. I'll post outcome then. Attached File
Attached File

Sounds good and thanks for the update.

Doesn't look too bad, so maybe as long as you can keep your torque to the minimum you might be able to get away with using the Geissele Reaction Rod on the next attempt. But lapping the receiver will likely change that, so you might have to shim the barrel nut to keep it at the low end of the torque spec.

In your case, clamshell upper receiver vise blocks would bias the pin to the side you need for good alignment with no real need to shim the loose side of the indexing pin.

This ^^^

Clamp the receiver instead of the barrel next time.

And of course, always be sure to liberally grease the forward side of the barrel extension flange (the side the barrel nut clamps against). Don't screw up a good upper like me.