Indicating a 6 groove rifle barrel with long stem indicator

zombiedfens · Aug 24, 2015

Hello,
I am by no means a professional, just doing this as a hobby. So please forgive me if this is a stupid question. I am setting up a rifle barrel in my lathe for threading and chambering. I am using a long stem interapid indicator to center the barrel. The barrel in question has 6 grooves and I cannot for the life of me figure out how to indicate using my 4 jaw chuck and rear spider. I have 4 points of adjustment yet 6 readings I need to dial in upon? Any hints or tips to get this done?

Street · Aug 25, 2015

If i where takling it i would put a plug in the end and locate off that, light tap fit with a slight taper at some point along to. Make it out of aluminum or bronze so it won't damage the bore go in a reasonable distance.
Not too tight you want to be able to get it out easily.
otherwise mark the chuck with paint pen for the land 1 to 6 and piece of paper for the runout figures and move the chuck just like normal except where it is inbetween you move 4 jaws in stead of just two. Think about it, should be straight forward, the paint marks on the chuck will help.

wesg · Aug 25, 2015

Whole bunch easier than one of those 5 groove things.

Start with using the grooves in one axis, and the lands in the other, to get close. Then you just need to be looking at all 6 and forming a picture of what you've got in your head.

Odds are the lands and grooves won't be lined up dead on with the chuck jaws anyway. But within 10 or 15 degrees isn't going to make a big difference in dialing it in.

Take it slow, tiny increments, and keep things barely snug until you're dead on at both ends. Then tighten it up in tiny increments, watching the alignment. If you tighten it up first and then try moving it you'll warp the barrel in the spindle and have no idea where it's all going to be when you take it out.

johnoder · Aug 25, 2015

Without the plug suggested in Post #2 folks must love doing things the hard way

300sniper · Aug 25, 2015

I find it easiest on any groove count barrel to start indicating on a "Grizzly rod" and fitted bushing in the bore, then verify with the DTI directly on the bore, fine tune if necessary. 99% of the time the setup is good to go without any fine tuning the way I do it.

michiganbuck · Aug 25, 2015

Think I would put the barrel between centers and indicate it to see how the OD runs to the ID near both ends and in the center. Put a strip of tape around to mark on (+.003, -.003 or what) Yes best to have a plug so not locating on the chamfer but to the ID. So a brass centered end plug would be made between centers to fit and go in perhaps 1".

For setting in the lathe:
You might make a mandrel that would be a round shaft that just fits to the ID and sticks out perhaps 4 inches to indicate on for run-out and straightness.
The mandrel would have to be made between centers to be accurate and perhaps difficult to make if a small bore like a 223 or so.. It might be made with a very slight taper at the go-in end so it interfere slightly to be a better fit to go in and slightly lock at some point.
The 4jaw might induce a wobble so actually try to bend the barrel perhaps best to have a short contact so perhaps wrap a 1/8 strip of brass around what is in the chuck so to zero the spider end and then work in the out end(chuck end).

*Perhaps you might try to zero the spider end and set the out end on your tail center then line up the steady then remove the center to see if that runs good. If that runs good a much easier method.But driving from the spider might not be good.

Another method is to set the barrel end in the 4jaw and the breech end in a steady. Then check to see how it runs. If that runs good another much easier method.

Jim Kobe · Aug 25, 2015

Get yourself the correct "ZZ" pin. You can get them in .0005" increments, they are .0002" undersize. If that ain't close enough you are just beating your head against the wall.

paracongo308 · Aug 25, 2015

Invest in a 3 or 6 jaw set tru and it will make life easier for just about all work on a lathe.

dero338 · Aug 25, 2015

I am not a professional either, but my favorite way to indicate a barrel is with a grizzly rod as explained in Gordy Gritters's video
Then indexing the thread for the barrel pointing up is a little more work, but I know everything is dead straight.

ulav8r · Aug 25, 2015

paracongo308 said:
Invest in a 3 or 6 jaw set tru and it will make life easier for just about all work on a lathe.

The adjust tru chucks still have four adjustment screws at 90 degree intervals on most. Bison chucks are(were) not at 90 degree intervals and therefore slightly more difficult to indicate.

Butch Lambert · Aug 25, 2015

dero338 said:
I am not a professional either, but my favorite way to indicate a barrel is with a grizzly rod as explained in Gordy Gritters's video
Then indexing the thread for the barrel pointing up is a little more work, but I know everything is dead straight.

No you are not.
I use double catheads to keep a chuck from bending the barrel. I have a set of Deltronic pins for each caliber that I chamber. They are in sets of 25 pins in .0001 increments. I indicate the pins on ea. end until the tenth indicator doesn't move. I drill the chamber and then use My 513-504 Mitutoyo to indicate the grooves. My Interapid indicator with the long probe jumps too much and takes much longer. I then taper bore to the throat. I want my reamer to follow the bored hole that is coaxial to the throat and not where a rod has wandered aimlessly through a bore. The purpose to indicating is to start the bullet in the center of the bore. Barrel bores to some degree are not straight, and they are not banana either. The idea is to get your chamber coaxial with the bore at the throat. No indicating method will straighten the barrel bore and I sure do not want the muzzle flopping on the other end.
I and several other people have tried the Gurdy method and quickly got away from it. I have modified my chambering method through the years as have a lot of people. Mine may not be the best way, but at this time in my mind it is.

James Lederer · Aug 25, 2015

Pretend the lands aren't there. For all intents and purposes you are only concerned about the grooves. If the lands weren't there, the grooves would make up a round hole. You can dial in a round hole with a 4 jaw chuck, right? Often the grooves don't make a perfect circle. So it does require some judgement to sort of mentally average the grove diameter and get the groove circle where you want it. Ideally you want every groove to present itself to the indicator the same way. In other words the needle should show identical movement and position for every groove. When I do it, I could care less what the lands do, they make up a small percentage of the bore anyway, and the bullet centers itself on the grooves when it is forced into the rifling.

Butch Lambert · Aug 25, 2015

James has made a barrel or 3.

zombiedfens · Aug 25, 2015

300sniper said:
I find it easiest on any groove count barrel to start indicating on a "Grizzly rod" and fitted bushing in the bore, then verify with the DTI directly on the bore, fine tune if necessary. 99% of the time the setup is good to go without any fine tuning the way I do it.

When you say "the way I do it" are you referring to the post you made awhile back with using a small weight on the Grizzly rod?

michiganbuck · Aug 25, 2015

https://www.grizzly.com/products/Grizzly-Rod-3-30-Cal-and-Up/T10772

paracongo308 · Aug 25, 2015

ulav8r said:
The adjust tru chucks still have four adjustment screws at 90 degree intervals on most. Bison chucks are(were) not at 90 degree intervals and therefore slightly more difficult to indicate.

Yes there is 4 adjustment screws on a set tru chuck, however your initial chucking is within a few thousandths OD ID concentric not a 1/16" or more starting with a 4 jaw chuck.

dero338 · Aug 25, 2015

I use a 3/4 nut to weight the grizzly rod and Just like most, I use a 1/8 brass rod to hold the barrel in a 4jaws chuck so barrel dont bend and chamber is perfectly aligned and centered with the bore.

Time being money, pros have equipment hobyist cant afford and when doing stuff for hoby, time is no concern.

wesg · Aug 25, 2015

paracongo308 said:
Yes there is 4 adjustment screws on a set tru chuck, however your initial chucking is within a few thousandths OD ID concentric not a 1/16" or more starting with a 4 jaw chuck.

I start with the barrel on a center in the tailstock, and snug up the tail end to hold it there. Then rough indicate the tail end. Barrel swivels on the center. Barely snug the screws at the front end to contact the barrel, remove the tailstock and start indicating.

Usually within a couple thou', and would probably be better if my tailstock was dead on vertically.

tdmidget · Aug 25, 2015

These folks LOVE the hard way. It has never occurred to them that these firearms were made by machinists, not gunsmiths. If they did it their way a single shot .22 would cost $5000,00. It wouldn't have a stock because all they think about is chambering and threading muzzles. It wouldn't have a trigger either except for the availability of store bought items.

300sniper · Aug 25, 2015

tdmidget said:
These folks LOVE the hard way. It has never occurred to them that these firearms were made by machinists, not gunsmiths. If they did it their way a single shot .22 would cost $5000,00. It wouldn't have a stock because all they think about is chambering and threading muzzles. It wouldn't have a trigger either except for the availability of store bought items.

And there's probably a pretty good reason a 700 fitted with a quality barrel by someone that took time to do it as true as possible shoots FAR better than an off the rack 700.

Indicating a 6 groove rifle barrel with long stem indicator

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