Chamber run out issue

[JerrySharrett]

Originally Posted by Bob Kingsbury

I I also don't know anyone who has a tenth indicator that reaches in to where the throat will be untill the prebore is done. Therefore, you cannot
indicate to where your going initially, only creating a guide.

.

The Interapid indcator does!!! Even with something like the Mitutoya, just predrilling will let you get to the throat of something like the PPC and BR.

[TRA]

Anyone ever try using an Air Gauge to indicate a barrel?

[AZLarry]

To: Shooter53

Did you indicate both ends of the barrel? No, I indicated the barrel from the chamber neck area forward for about 1/2" inch. Looking back maybe I should of indicated farther into the barrel (ie: add up the neck length, free bore length, throat angle and reamer bushing it is about 1" of total length.

How well did you indicate bore ( in thousands)? .0002-3" with 2.750" long stem interapid indicator. Not the best setup up but only one that can go that deep with the small bolt face cartridge.

What is the runout spec on your lathe's headstock? .000050" (Hardinge toolroom lathe)

[Don]

Originally Posted by TRA

Anyone ever try using an Air Gauge to indicate a barrel?

Air Gauge measures bore diameter differences not bore position in a lathe........Don

[Shooter53]

AZLarry

Your lathe headstock runout is more than adequate (great actually) so that is not the problem.

You indicated the breech end of the bore well enough so that is not the problem.

Understand, if the muzzle end of the bore is off center by just 0.007" to 0.008" that can wobble the breech by at least 0.001" on a 26" barrel.

I know you indicated the bore at the breech 2-3 ten thousandths at a distance of 2.75" but you may not have had enough depth in the bore to really align the indicator.

The PTG indicator rods are machined to be used on an already chambered barrel with such a fine taper as to allow the rod to set about 2" into the bore past the freebore.

The range and indicator rods are less than $40 each. Having both and being able to indicate both ends of the barrel is very effective and allows you to see how much movement the breech end travels for a few thousands of movement at the muzzle.

I'm sure there are better ways to accomplish the same thing but I thought I'd just throw out a quick and easy way to get there.

Good Luck

[TRA]

don

I understand what an air gauge is for, just was thinking out of the box, IE, some form of non-contact method of centering a bore.

If you predrill a recess in a barrel and then indicate, and correct at the throat, that will not mean the chamber is parallel to the bore.

Another thing to keep in mind is that most indicators are calibrated with a probe of about 1/2" long, when you replace that with a long probe your "tenths" are no longer "tenths".

[Bob Kingsbury]

I have both of those indicators, and I use them. They almost make it
the needle is set to one side a bit, and that detracts from the 3/8
diameter nose. I can indicate the front of the neck, but when in the throat
you are actually at 7:30, not an ideal 6:00.

[Zebra13]

Originally Posted by Shooter53

Understand, if the muzzle end of the bore is off center by just 0.007" to 0.008" that can wobble the breech by at least 0.001" on a 26" barrel.

Are you talking about a barrel set-up as AZLarry describes, i.e., breech end held and indicated in on a 6 jaw chuck and apparently, as I understand it, the muzzle end not indicated in?

Justin

[AZLarry]

To: TRA

The Interapid indicator described is made to operate with a 2.750" stem with a resolution of .0005" on the dial.

To: Shooter53

I'm following the principles described by Gordy's video on barrel alignment. Bore alignment only at the chamber area, what the muzzle is doing is not critical.

To All:

I have made a few changes to my setup:

1) Made the alum. split ring holding the barrel in the chuck thinner. Last week I was using a 3/8" wide piece, changed to a .060 width so the barrel can "pivot" easier with the muzzle end spider.

2) Modified the floating reamer holder with a spring for stability but still be able to move in all directions for proper alignment. Also changed it so I don't have to hold the handle while the reamer is cutting. If I get the wife's digital camera I'll take a picture of it. Interesting contraption. *If does not work as planned will have to "simplify" and go with the Mr. Bryant type of holder.

3) Will try to indicate the bore from the neck to the end of the reamer. Will leave off the reamer bushing.

4) Will pre-bore the chamber to 1.425 (just short of base to shoulder length of 1.432") depth with a .4 degree taper. Leaving .005" on each side for the reamer. The closer I can get to a finished chamber BEFORE reaming it can't hurt. Hopefully!

Should have this "experiment" started within the next week. Will keep you posted.

Always good to hear from you all. Your input is very helpful.

Thanks, Larry

[Don]

Originally Posted by TRA

don

I understand what an air gauge is for, just was thinking out of the box, IE, some form of non-contact method of centering a bore.

".

Guess I dont have "out of the box vision"..........how do you center a bore in a lathe with an air gauge?..............Don

[JerrySharrett]

Originally Posted by AZLarry

. Bore alignment only at the chamber area, what the muzzle is doing is not critical.

Larry

Let me get this straight in my mind, you are concerned with 0.0015" runout in the chamber body of a 223 Remington but where the muzzle is pointed, the exit point of the bullet, does not concern you???

[Shooter53]

AZLarry,

Sorry, I'm not familiar with Gordy's method of barrel alignment.

My reference is from Darrel Holland's 2 video set "Custom Barreling" from AGI (American Gunsmithing Institue), The Gunsmith Machinist by Steve Acker and "The Complete Illustrated Guide to Precison Rifle Barrel Fitting by John L, Hinnant.

Good luck with your project.

[Boyd Allen]

Link to a excerpt from Gordy's barrel setup video
http://www.youtube.com/watch?v=aII2tbavKnM
It looks like he has possibly used double stick tape to hold shims onto the faces of the chuck jaws, and that they only extend a short distance down the barrel, allowing it to pivot. Also note, he doesn't need a long skinny indicator to reach down the barrel. Dave Kiff sells the rod that he is using. It takes reamer pilots on one end and is just barely into the tailstock chuck on the other.

[Bob Kingsbury]

When both ends are indicate,to the bore, there is a plus for benchrest
shooters. That one barrel can be removed and another put in its place
seldom takes you far from the point of aim. Had the muzzle been on its own
in a spyder, its a guess. When you can change barrels and the first shot is
an inch off at 200, something is right. There not always that close, but
you know where they are.

[jackie schmidt]

One of the best Benchrest Shooters in the World, (and I do mean "the World") does his barrels by aligning the first 2-3 inches length of the barrel's ID dead true, and cares nothing for how the muzzle end is running.

When he does a barrel, it is a little strange to see that muzzle end running out, but the results speak for theselves....on the target.

..........jackie