Gunsmithing need some help on an out of the ordinary chamber issue.....

[selfbowhunter]

I just chambered up a shilen #2 in 6.5x47 for a light weight hunting rifle. while measuring runout I encountered something that I just cant wrap my head around! my setup is like most here. I use a spyder on the outboard and either a 4 jaw or spyder on the inboard depending on the length of the barrel. I indicate the grooves on the chamber end as close as I can get to the eventual throat, then I indicate muzzle end and shoot for less than .0005 runout front and back before I start the work. I always pre bore the chambers as well. I measure the chamber after polishing and before removing the barrel from the lathe to make sure all is ok. well this doesn't seem ok! I started at the rear of the chamber and had .003 TIR!!! moving forward it got less and less. the neck area of the chamber and throat are as close as I can get them at less than .0005 runout. HOW IS THIS EVEN POSSIBLE? should I bore the 6.5x47 chamber concentric to the throat area and punch it out to .260AI? I was wanting something with very moderate recoil due to neck issues and didn't want to go that big.
the barrel is already 20" with less than 1" of shank before the taper so I don't think I can cut it off and start over. would it be worth even seeing if the thing will shoot?
chuck

 

[Gene Poole]

I'm not sure I got this straight. Did you indicate at 2 places: the muzzle and the (eventual) throat? My understanding is that you ignore the muzzle end when chambering and indicate at the throat and at the bottom of the chamber (the bore can wander before it reaches the muzzle). Was this with a piloted reamer and a floating pusher?

 

[selfbowhunter]

indicated at the throat and muzzle end. the method you speak of is how Gordy Gritters does it. I would say that more people do it with this method than that! piloted reamer with the proper bushing installed. pushed with a dead center. I do have a pusher I made that is the same as what mike Bryant and many others use. didn't use it in this case but I don't see how that would matter other than making the end of the chamber oversize. don't think it could induce runout.

chuck

 

[buffybuster]

The bore wanders a bit from breech to muzzle. If you proceeded on the assumption the bore was dead straight, that would be a mistake.

 

[selfbowhunter]

The bore wanders a bit from breech to muzzle. If you proceeded on the assumption the bore was dead straight, that would be a mistake.

I didn't assume the bore was straight. the chamber end was indicated in AT THE THROAT. the chamber was PREBORED concentric to the throat. this should have alleviated any issue with a wondering bore shouldn't it? how could I have no runout where the chamber was indicated at the throat and have runout at the end of the chamber?

chuck

 

[jonaddis84]

Im thinking the only way you could end up measuring runout after chambering is if the barrel moved in the lathe during or after the process. Otherwise you would just end up with an enlarged chamber like you said. If say your prebore was cut perfectly, then while chambering the barrel shifted slightly, the reamer would still follow the prebore, and if you measured after chambering it would show runout.

Now back on the indicating process, Im still confused. I would say the way the majority of guys do it is all the indication is done in the chamber end. Whether you use a range rod or direct indication, you ignore the muzzle because who knows how straight the bore was drilled, you want the chamber to be concentric with the bore just after the chamber. This may be the way you are saying, but its hard to tell.

And to answer the other question, if the chamber is in fact true to spec and not oversize, I would just shoot it.

 

[selfbowhunter]

so most folks use the Gordy method, a range rod, or direct indication ONLY ON THE CHAMBER END? I have read that a range rod will never read the same when removed and replace after being dialed in dead nutz. I do have some Gordy rods. I think the next chamber I will try his method and see what happens. do you indicate at the throat an an inch or two ahead or do you indicate at the throat and rear of the chamber with YOUR method? thanks again for the help.

chuck

 

[Killswitch Engage]

I just don't think indicating the muzzle is a good idea. Barrels just aren't straight enough...if ever to indicate both ends at once. Indicate the end you are working on and go on. You more then likely induced some unwanted stress in the barrel that didn't want to be there. As for .003 tir at the back of the chamber that's not the end of the world or nearly the worst I've seen. If its a hunting rifle....run it.

 

[selfbowhunter]

I will try just indicating the breech end on the next one. I still don't understand where the runout could have originated with a prebored chamber.

chuck

 

[Killswitch Engage]

When you indicated both ends I guarantee you induced unwanted stress on that barrel. It would be my guess things started moving a little as material was being removed for the chamber. That's my .02

 

[jonaddis84]

so most folks use the Gordy method, a range rod, or direct indication ONLY ON THE CHAMBER END? I have read that a range rod will never read the same when removed and replace after being dialed in dead nutz. I do have some Gordy rods. I think the next chamber I will try his method and see what happens. do you indicate at the throat an an inch or two ahead or do you indicate at the throat and rear of the chamber with YOUR method? thanks again for the help.

chuck

Yeah I dont like range rods for that reason, but you can still indicate just the breech end with a direct method.

Set up your blank in there as normal. I grab my long reach indicator, lay it on the outside of the barrel with it positioned as if it were inserted as far as it could possibly go into the barrel (shank of indicator and all), then set the barrel protrusion from the chuck so that the indicator tip is right on the pivoting point (in my case this is at the end of the aluminum jaw pads). You need some kind of soft jaw pad here or else you will be inducing a large amount of stress into the barrel when you adjust your outboard spider, mine are about 3/8" long where they touch the barrel.

Now indicate the bore in as best as you can, just within .0005 or even a little worse is ok here. Now pre-drill the bore, on a 6.5cm ie I use a .400 drill so its plenty smaller than the smallest diameter of the chamber. Drill this 1.2" (or however long the shank on your indicator is), dont think that longer is better here because you need the rifling intact to indicate off of. needs to be at least .380 or so on most indicators so they will fit into that hole. Obviously if you are chambering a 223 or similar you wont be able to use this exact method.

Now indicate the bore perfect, within .0002 or whatever your favorite number is. The reason for setting the barrel protrusion earlier will become apparent here as it is much easier to indicate when you are adjusting the chuck right where the indicator is measuring, this way when you adjust the outboard spider it doesnt affect the inner adjustment at all.

Now BORE it, just enough so that youve cleaned up all sides is enough, make sure you stay below the smallest reamer diameter.

Now chamber it.

 

[selfbowhunter]

that's basically how I do it! tell me this though. if you are using your indicator at the throat which is the pivot point and you are only interested in the breech end, why are you adjusting the outboard spyder at all?

chuck

 

[Killswitch Engage]

Because you need it adjusted coaxial at two points. Even if you are running your indicator into the bore and going where the throat is going to be you still need to indicate out at the very end of the chamber as well to get coaxial alignment. That's why you pick two spots on the range rod or whatever you use.

 

[selfbowhunter]

well, I went out to look things over again and had decided I would just punch the thing out to .260ai after I was satisfied everything was right. what I discovered is that nothing was wrong other than my setup. when I started out, a very well respected smith schooled me on chambering and advised that I use weed eater string in the 4jaw to keep from inducing stress to the work piece. I did this for a couple years and started using heavy copper wire because I felt it would be more secure (though I never had the slightest issue with the weed eater string). a while back I ran out of copper wire and ran into a guy in town that went to the gunsmithing school in Trinidad. he suggested I use pennies in the headstock since that's what he uses and he said it worked great. we evidently, a penny has too much bearing surface and doesn't allow a barrel to pivot because I set the barrel up as stress free as I possibly could (not using pennies, or my 4jaw for that matter) and I now have well under .001 TIR at the rear of the chamber after the throat is dialed in to as close to .0000 as I can get it! it seems that some residual stress revealed itself as runout after metal was removed from the chamber. would have never believed it but I just proved it to myself anyway.

chuck

 

[Killswitch Engage]

Sounds like you found your monster. How come you don't save your copper rings and reuse them? I've heard of the weed eater string and even o-rings but have more faith in the copper staying put yet letting things pivot. Good thread!

 

[Gene Poole]

I posted this a few days ago in response to a thread on muzzle threading. It's the same basic concept; just on the other end of the barrel.

You can see my copper ring in there at the same point as the tip of the DTI when inserted.

As mentioned earlier, I ignored the runout on the other end and just went for concentricity at the business end, but it was not insignificant (I could see the wobble while running the spindle).

VIDEO0063-0.mp4 - YouTube

 

[jonaddis84]

that's basically how I do it! tell me this though. if you are using your indicator at the throat which is the pivot point and you are only interested in the breech end, why are you adjusting the outboard spyder at all?

chuck

Just like KE said, you are moving the indicator back and forth the length of the indicator and adjusting accordingly. So with the indicator fully into the pre bore you adjust the chuck, then with it pulled out to the edge of where the rifling meets the pre bore you adjust the spider.

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[bear458]

I will try just indicating the breech end on the next one. I still don't understand where the runout could have originated with a prebored chamber.

chuck

Even if the barrels bore is not aligned with the spindle. the bored hole will be. A piloted reamer will follow the bore the boring bar won't,
FWIW Next time try this, mount your copper ring over the spot where the front of the chamber will be, indicate off the bore, not the grooves (the bore is reamed the grooves are cut), then retract the indicator to where the rear of the chamber will be, use the out board (muzzle) spider to bring in zero there. Recheck. This will align the first several inches of the barrel with the centerline of the spindle. Don't worry about the muzzle. Now you have the chamber end aligned and a bored then reamed chamber will be concentric with the hole already there.
At this point I would mark the high spot of the muzzle on the chuck so I could clock the action to the barrel (high spot on the muzzle at 12 o'clock to the action) Works for me, even with a barrel that's not very straight they tend to shoot pretty well.

 

[selfbowhunter]

I am going to try to get me hands on some range rods to give that a whirl. I do have some grizzly rods I could try as well. in any case, I will try one only work on the breech end and let the muzzle do what it will.

chuck

 

[bear458]

For me, The grizzly rods with a snug to the bore pilot, indicator close to the barrel, is the most accurate for me

 

[Straight Shooter]

Chuck,
The .003 in the length of the chamber sounds exactly normal for the way the barrel dialed at both ends.

We use the Gordy method because it's the only way to get the chamber aligned with the path of the bore right ahead of the neck. We only care about the end we are working on. For a chamber it's at the neck/throat and 2" farther in. Then drill and single point. I want the chamber pointing perfectly into the 2" ahead of the throat. A crown or muzzle threads are dialed at the crown and then 2" back. On the chamber end if you dial the throat and then where the chamber is it can still be misaligned with the actual bore from the throat forward. Our spider chucks are brass pointed up to a 1/8" contact point. If they would hold and last they would be sharp. You can really tweek a barrel with a chuck with wide contacts. The only thing we do that Gordy doesn't do is use a high pressure flush system.

 

[mcfred]

I'd go try it out; I bet it will shoot fine. Have you ever seen a remington chamber?

 

[selfbowhunter]

I have been shooting the shit out of it and its going to be fine. I will definitely try the gordy method next time as the more I think about it the more I come to understand what happened. I think for my method a LOOSE bushing or none at all would keep the bore ahead of the throat from trying to manipulate the rear of the chamber. in this case it was induced stress and I wont make that mistake again. I figured the guy learned a thing or two in Trinidad. that what I get for thinking.

chuck

 

[Straight Shooter]

I don't think stress had anything to do with it. If you dial the throat and muzzle to zero run out those are the only two places that will be dialed. As you move your indicator out towards the chamber you will start picking up the curve in the bore. If you bore and single point the chamber area it will look fine until you put a borescope in it and then you will see rifling starting closer on one side than the other indicating that the chamber is pointing into the side of the barrel. Meaning even though you are centered the barrel is curved right in front of the neck.

Like Mcfred said. They can still shoot even crooked as hell.

 

[selfbowhunter]

what about the TIGHT bushing following the curve in the bore ahead of the throat? are you telling me that doesn't induce any stress or cause any issues behind it?

chuck

 

[Killswitch Engage]

We're not talking about banana curvature here. We're talking a few thousands to probably .020 at the most on a really curved barrel over 26-27". Depending on how much you had to bend the barrel with the outboard spider to bring the muzzle to zero runout there is very easily added stress on the barrel. Add to that the fact that there was little to no pivot point in the chuck even more stress. This is IMHO the reason for coaxial indicating the bore only on the end you're working on at two points. Then your nice tight pilot follows the bore and the back of the reamer isnt being shoved around or flexed since the back of the chamber is indicated as well as the throat. Even if you don't prebore the chamber.

 

[Straight Shooter]

I was talking about your chuck bending the barrel. We see that if the bolts are too tight. There is no way the reamer bushing is stressing your barrel. I'm pretty sure the tip would break off your reamer before you could measure any changes attributed to that. If you don't drill and single point all the dialing is for not anyway. The reamer will just follow the existing bore and you end up with a slightly oversize chamber. Most guys would never knew it happened unless you made a casting and measured it against the reamer.

 

[Killswitch Engage]

There's arguments for prebore and not. I've seen perfect chambers come from just plain ol reaming the whole thing. It's all about the set up.

 

[Straight Shooter]

I guess the definition of perfect might be in order. My definition is when the chambering job is done we check the run out in 3 places. The beginning edge of the chamber, the throat and then 2" into the bore past that. Our method yields zero in all 3 spots.

Assuming still in the lathe, I would bet money that just shoving a reamer in the bore and playing follow the bore it will only measure zero at the throat.

It doesn't mean it still won't shoot pretty darn good. Might even set records with it. I was just showing how I do it here.

 

[Killswitch Engage]

I definitely won't argue that prebore won't provide awesome results but I will say a barrel was chambered today with just the reamer and tir at the throat and edge of the chamber was under.0002. Actually the last two chambers. It can be done if you're not in a rush and trying to make money.

 

[Straight Shooter]

That .0002" is a reflection of the natural curve in the bore. It would be far easier and faster for us to use ram reamer start to finish. Whether you feed it fast or slow, the run out numbers will be the same. The purpose of drilling and single point preboring is nothing to do with saving time but correcting the chamber area into line with the throat and 2" of bore. My goal is not to just get it done. It takes what it takes. I won't be rushed on it. My payment is seeing that smile when a guy finds out after all these years he really can shoot much better than he ever thought possible.

 

[jonaddis84]

I wouldn't expect too many chambers to be cut from a finish reamer without any prebore....

Preboring is good all around, saves time, saves reamer life, and makes sure everything is lined up for the reamer to follow.

Not to mention, at least IMO, you can't indicate it properly UNLESS you prebore. Unless you have some super special indicator with a 4" tip that still reads close to .0001", which I doubt. Otherwise you are indicating the bore where the chamber is going to be, not where the bullet is going to start it's journey.

This is all said with the assumption that we ARE splitting hairs when we discuss this stuff. I bet if you threw a good quality barrel in a 3 jaw and shoved a match finisher in there with proper headspace, it would still shoot.

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