Indicating a barrel for chambering?

So I'm about to chamber up a new 7mm brux barrel and I'm a little stumped. Normally I just use a range rod with the proper fit bushing and dial in the barrel on the chamber/breech end with my mitutoyo .0001" Indicator to as close to zero run-out as I can get and don't worry about the muzzle runout. this was my normal way of chambering and I index the muzzle to 12oclock.

This time I used my mitutoyo .0001" dial with a 2.8" long tip. I dialed in at the breech and then about 2.6" in to the barrel. I was dialing in on the groove and got it running damn near zero runout at both spots.





the muzzle end of the barrel was running about .050" out of round and you could visibly see the barrel was way out of being concentric at the muzzle end.

so I grabbed my range rod and .0001 indicator and dialed the muzzle end into about .0001" runout



I then went back and checked the far chamber end and it was still running almost zero run-out. I then ran the long indicator into the bore about 2.6" and it had a measured run-out of +.0005" now.

SO what is the best way to go about this? I'm still learning and I'm not sure if I should chamber it with zero runout at the breech and 2.6" in or should I get the muzzle dialed in and the breech and don't worry about the run-out 2.6" in from there?

I use a floating reamer holder and chambering with a flush system, I use a finish reamer start to finish and do not prebore.

Did you do the math on that "long reach" indicator tip?

Can't possibly be the same as with a short tip.

I haven't done the math myself but I read a post awhile back I think its around .0003" when you add the long tip. But its not even moving on the indicator.

I'm mainly looking for someone with more experience than myself to tell me which is the correct method. just dial the section that is going to be chambered in for zero run out and not worry about the muzzle.

Or does the muzzle need to be concentric with the chamber end? because .050" runout seemed a lot to me.

I'm no gunsmith, but either your barrel is a banana shape or the chamber you are getting ready to ream was not cut correctly. First determine if the barrel is banana shaped; if it is, throw it away. If the barrel is strait then indicate both ends concentric and learn how to bore your chamber. After concentric cleanup you can go back to your reamer.

The barrel is brand new, no chamber cut yet. Im dialing it in to chamber it. I know all barrels have some curve to them I'm not sure how much as ive only chambered 4 barrels so far and non of them had this much curve to them.

if you re-read my post I did dial in both sides of the barrel. then ran my long reach indicator in the bore about 2.6" and the run out was .0005" is that expectable since I'm going to be using a floating reamer holder?

Or do I just want to dial in the chamber end of the bore in two spots to zero run out and leave the muzzle where ever it is.

Think about it, the difference in length, the chamber 2.6 reach versus the barrel length, 26". Ten times the error from the chamber to the muzzle end. In theory, if the barrel is "straight", which we all know is not, and you have say .0003 at the chamber, you will have .003 at the muzzle, theoreticallty.

Your method is probably sound, you just have a blank with a lot of walk in the bore. 50 thou at the muzzle is probably too much. Using this method a barrel from a good manufacturer will typically have 10 or 12 thou runout at the muzzle. I had one about 0.024 that I sent back and the manufacturer (Bartlein) happily replaced it.

Forget about the muzzle and prebore the chamber once the chamber end bore is dialed in by whatever method you like.. For my money, the important thing is to have the bullet launched into the bore in the best possible alignment with the immediately downstream bore segment.

RWO

I work between centers, but know a lot of smiths have moved from the rods, to the long-stem indicators as you've done when working through the headstock. I've never had much confidence in a long, skinny steel rod being all that..., anyway. If you're perfectly dialed in at the chamber end- the bullet's gonna be launched perfectly straight into the leade. You can't control what happens inside the barrel past that, IMO.

Here is how it's done:

Direct barrel indicating - YouTube

and here is why you only indicate the end on which you're doing work:

Dialing a barrel in on both sides of the bore. - YouTube

I've been doing this for a while now and have come to the conclusion there's a lot of bent barrels due to holding between chucks. I find it hard to believe that any precision barrel maker is allowing for .001"-.002"+ of deviation over 1". Barrels are not very rigid when you start jacking them around trying to get it to conform. Ways I swore up and down were the best a couple years ago, I now question and no longer use.

May like to go to this site and read this thread:
1911Pro.com • View topic - Last several weeks of work in pictures
There is some real good information here about adjusting a spider to get the least runout for chambering operations...
Jerry Keefer is a top notch smif and is very generous with his processes.
His posts there are mostly related to short aumatic pistol barrels but he also works on rifles and shotguns so I think his work may relate to your issue.
Joe
There is also another thread about floating reamers that could help:
1911Pro.com • View topic - NEW stuff / new techniques

Work off the chamber end and let the muzzle go (not bent or forced) -- or send the barrel back.

Toss your barrel shank in a decently parallel 4 jaw and dial it in so where the throat will be is running dead nuts. Shove your indicator in another inch. Measure the runout at that point and at the muzzle. Does the math jive with your current setup?

300sniper said:

Toss your barrel shank in a decently parallel 4 jaw and dial it in so where the throat will be is running dead nuts. Shove your indicator in another inch. Measure the runout at that point and at the muzzle. Does the math jive with your current setup?

Click to expand...

This was my problem. By adding the long stem to my indicator it changed the value more than I thought. I put the short contact point back on and checked the breech side and it was .0005 out

I then put my range rod in and check and it was out about .001 on the far end. This is why was getting such crazy readings