Jerry Sharrett pix, HAPPY THANKSGIVING!!

[alinwa]

OK Jerry, I'm gonna' try this.....

I'll do it in a series of posts. Try not to get loooong.

Step #1-

I decided to rechamber an old 6BR barrel to make a 6X47L ff barrel. The guy who fitted this indicates both ends so I decided to set it up this way for starters. I want the chamber to be square to the threads. So I set it up as shown here, dialed in muzzle bore on outboard side and chamber on headstock side. In my opinion this setup is centered on the axis of the machine as well as if between centers.

(For now we'll assume the machine is true..... NO allowances made for play/slop/flex etc)

Setup is FINGER TIGHT on both ends..... no bending.

Muzzle dialed to zero in spider

chamber dialed to zero

Pix below.

#1- pic of lathe to show overview of setup
#2- pic of headstock side, chamber indicator
#3- pic of outboard 'spider' side
#4- closeup of spider assy

 

[alinwa]

Step #2-

Now I've got the barrel floating in the headstock, both ends indicated to center. I COULD just tighten 'er down and go to town. As it sits it's centered up as though between centers.

But I want to reach in and find the throat..... And furthermore, I want to reach 'WAYYY in and check out the inch or so BEYOND the throat, find out if it's wandering.

So I do, as shown below.

#1 shows the setup, indicator riding on rod just outside of chamber, the rod extends into the barrel and is resting on the lands just beyond the leade.

#2 shows that the Grizzly Rod is just barely chucked into the tailstock chuck. It's not floating in the bore, in fact no attempt is made to center it up. I presume misalignment and furthermore chuck it so shallow that it HAS to be just setting in the bore.

#3 is just backed off view to show setup.

 

[alinwa]

#3-

I'm now going to hang a WEIGHT on the Grizzly Rod to absolutely force it to the "bottom" of the bore. I'm indicating off the lands only, bottom of bore. The weight will ensure that the Grizzly rod doesn't try to climb the bore on me.

If you look closely you'll see that along with the weight I've marked dots on the Grizzly rod for the three spots I'm checking.

I've taken a bunch of notes.... I've written down my BEFORE weight runout (I've found about 9/10 runout at the throat) I've got the barrel marked for indexing. Before adding the weight I'm showing almost a thou of runout in the throat, back to zero an inch in and about a thou THE OTHER WAY at two inches in. My measurements indicate that the chamber is cocked to the bore centerline with a total of .002 banana in the three and 1/2 inches checked.

After adding the weight to the Grizzly rod I get the same measurements.

This chamber is definitely cocked.

So now I can either dial the muzzle around, jack it with the spider to bring the work area to straight..... or

on to post #4...






pic #1 is checking the throat area

pic #2 is checking a point about 1.5 inches beyond the throat of a 6BR chamber.

edit.... as you can see I'm actually checking a point nearly 3" beyond the throat or about 4.5" into the barrel.

 

[alinwa]

OK..... last post.

I've decided to just leave the barrel indexed as though between centers BUT with one change. I'm now centered on the THROAT and the outboard MUZZLE.

-I've tightened it down
-I've RECHECKED and the runout is still there. Now the mouth of the chamber has a thou of wobble.

I'm an experimenter, soooo, I ran a bit in and bored out the thou of wobble. Now HOPEFULLY I've achieved alignment between 3 points. Muzzle, lands near throat and rear end of chamber.

All's I want is a fireform barrel so now I'm running a 6X47L reamer in..... I'm hoping that the remaining wobble will just get absorbed by the system and I'll get a chamber that's perpendicular to my boltface. If not, then I've got some really nasty cleanup to do......

Meantime, can you do me a favor???

Here's a pic of my reamer driving setup. I made a holder that is designed to be pushed with the tailstock chuck. ONE part, just the holder, no separate pusher plate.

What'cha' think all???

please critique

-setup?
-grizzly rod?
-reamer holder/pusher?

Thanks and Happy Thanksgiving to all!

al

reamer holder and pic showing relationship to tailstock chuck (which retracts fully to present a circular machined surface.)

 

[alinwa]

I just had to add one more item....

This is a thoroughly used barrel. I got some iffy bouncy measurements in the baked-out throat area so I scrubbed 'er out and ran the indicator rod 'wayyy into the bore. I have no idea whether the bore is actually "wandering" or if the original chamber is just cocked a little. My guts tell me the bore is cocked just over a thou in the length measured. But it could just be sloppy wear. I'm trying to get a chamber that'd aligned to the threads. I don't know how to really know this until I've fired some rounds thru the new chamber. The shoulder indicates true to my setup but it's been on-off two different actions a hunnerd times.

I'll let y'all's have at it now with the critique. Please look at the SETUP not at the obvious problems inherent to trying to dial in an old barrel.

thanks

al

 

[JerrySharrett]

In the previous thread, post #16 I wrote "Deltronic pins, range rods or Grizzly rods, in none of these are you indicating the point where the rubber meets the road which is where the freebore/leade merges with the barrel bore. "

I repeat "Deltronic pins, range rods or Grizzly rods, in none of these are you indicating the point where the rubber meets the road which is where the freebore/leade merges with the barrel bore."

I don't see how else I can put it!!

 

[JerrySharrett]

I can see where you are greatly reducing the resolution of your dial indicator by measuring a greatly reduced movement of thatever the freebore/leade happens to be by where the indicator stylus is on the "rod" thing (whatever you chose to call it).

I can also see where you are inducing potential and probable measurement error with the three contact point setup you show ( contact point #1 is where your bushing contacts the barrel bore, contact point #2 is where the "rod thingy" contacts the bushing bore, and contact point #3 is where your dial indicator contacts the "rod thingy"). i.e If you had placed the stylus tip just in front of the drill chuck in the tailstock the measurement would be near zero. Instead, you are attempting to measure a movement that is still a considerable distance outside there the freebore/leade will be.

In your setup with the "rod thingy" you are not even using that tool for what it was designed for which is to attempt to get an averaged alignment of the chamber end of the barrel bore.

In any instance I thank you for posting and I think the viewing and comments of this thread is something we all may learn something from (what to not do as well as what to do for best accuracy).

Happy Thanksgiving to al and all. We all have something to be thankful for!!

 

[JerrySharrett]

OK..... last post.


Meantime, can you do me a favor???

Here's a pic of my reamer driving setup. I made a holder that is designed to be pushed with the tailstock chuck. ONE part, just the holder, no separate pusher plate.

What'cha' think all???

please critique

-setup?
-grizzly rod?
-reamer holder/pusher?

Thanks and Happy Thanksgiving to all!

al

reamer holder and pic showing relationship to tailstock chuck

A suggestion here, if you will shorten the pusher handle to where it could spin freely in event of the reamer grabbing the setup will be safer. As you show it, if for some reason you loose your grip and the handle strikes the bedway something bad will happen for sure.

 

[Dennis Sorensen]

I think the Grizzly rod set up with weight hanging on it will indicate quite accurately as any 'slop' in the fit of the bushing to the bore or of the bushing to the rod will be always be held against the bore, just as a long spring loaded indicator point would be.

I would certainly shorten the handle so that it can swing without jamming on anything and hand hold it. I use one with about a 4 inch handle and I can hold it with no trouble. You definitely can feel how hard you are pushing it.

 

[Jeffrey]

In the previous thread, post #16 I wrote "Deltronic pins, range rods or Grizzly rods, in none of these are you indicating the point where the rubber meets the road which is where the freebore/leade merges with the barrel bore. "

I repeat "Deltronic pins, range rods or Grizzly rods, in none of these are you indicating the point where the rubber meets the road which is where the freebore/leade merges with the barrel bore."

I don't see how else I can put it!!

Well, your geometry is correct so the Grizzly rod only works when the run out is "0" at every location, which I think was it's intent.

Does anyone indicate the land height to the groove before they start "dialing in", or is it just me wasting energy. I have found one barrel where one land was .0005 taller then the rest. You can often tell when a range rod isn't seated correctly, or when the land diameter isn't true, by the way the indicator reacts. Setting up using varied methods to confirm is probably the best idea.

Jeffrey

 

[Butch Lambert]

Al,
I do a setup that starts initially with Deltronic pins in each end. I predrill and then use my 513-504 Mitutoyo small body indicator to reach into the drilled hole and indicate the leade area. I indicate the groove. I do not like my long probe Interapid for this as the probe is flexible and jumps around. The Mitutoyo has a 1/2" probe. At this time I use a carbide boring bar and taper bore the chamber. This gives me a hole that is running true with the spindle bearings and will allow the flutes to follow the bored hole and not the bushing. I use a loose bushing. My idea is to have everything coaxial with the spindle. I made a pusher similar to the Bald Eagle.
Critiques?
Jeffery, I am doing that when I indicate the leade area. You have to in my method. The only ones that I find that have a problem and is is very little;.0001, is the cut rifled barrels or hammerforged barrels.
Butch

 

[JerrySharrett]

I think the Grizzly rod set up with weight hanging on it will indicate quite accurately as any 'slop' in the fit of the bushing to the bore or of the bushing to the rod will be always be held against the bore, just as a long spring loaded indicator point would be.

.

I agree with the slop issue but why decrease the measurement resolution by about a factor of four when he has the capability, as shown in post#1, photo #3, to measure directly????

 

[IndianaJames]

I agree with the slop issue but why decrease the measurement resolution by about a factor of four when he has the capability, as shown in post#1, photo #3, to measure directly????

Because it's easier to measure on a smooth rod than land groove land groove land groove land groove????

I've wondered about the land height variance mentioned by Jeffrey above. How common is it to have different height lands?

Jim

 

[4Mesh]

Because it's easier to measure on a smooth rod than land groove land groove land groove land groove????

I never minded using the instrument right on the lands/grooves. I guess that's just me.

I've wondered about the land height variance mentioned by Jeffrey above. How common is it to have different height lands?

Jim

Not very likely, since it's the tops of the lands that were done with a drill and reamer. The bottoms of the grooves are where you would expect to see variation, if there were any. In my experience with both button'ed and cut barrels, it is slight.

Al, thanks very much for your amazing effort in producing this thread. Since I don't have a lot of time to study this, I'll have to give it some thought before finding fault or promise. Like Jerry, I can see a lot of issues forthcoming here. Not the least of which is that you've said this barrel has been installed / re-installed many times. That alone means it's been in a vice many times, exactly where you are measuring. These things do crush.

I'll have to think about it more... Thanks again, and Happy Thanksgiving to all. Time to leave for dinner! WhoooHooo

 

[Boyd Allen]

Al,
One spectator question....Why be saddled with the original tenon and shoulder? If you want the chamber to line up perfectly with the action (Hopefully the bolt face is perpendicular to the action threads and parallel to its face.) you could chamber just short of full depth, and then reindicate off of the chamber and then cut a new tenon and shoulder. I'm just asking.

 

[Wayne Shaw]

Variations in the top of lands do happen, as do variations in the grooves. If you watch a good indicator while slowly rotating a barrel, you can see it. I doubt it is from the tooling used, be it cut or button. I believe it is from the lapping. It's common to see a variance in the groove between land to land, such as a "belly" in the middle. It's not a consistent arc, as it should be. I would imagine it's not easy to get an even coating of lapping compound all the way around, and in all places.

And to top it off, the bullet obturates to the internal profile of the barrel. Any variance inside will be mirrored on the bullet.

 

[alinwa]

In the previous thread, post #16 I wrote "Deltronic pins, range rods or Grizzly rods, in none of these are you indicating the point where the rubber meets the road which is where the freebore/leade merges with the barrel bore. "

I repeat "Deltronic pins, range rods or Grizzly rods, in none of these are you indicating the point where the rubber meets the road which is where the freebore/leade merges with the barrel bore."


I don't see how else I can put it!!

Thanks Jerry, I finally see what you're saying.... I think. You're saying that the true story is told in the GROOVES not up on top of the lands. I can't disagree with your logic.

Regarding the handle. Thank you, good catch. I should have used the short handle for the pix. The handles are hunks of 5/8 rod stock w/1/4-28 allthread....... I kinda' am still fiddling with them (smooth/knurled/straight/bent) I was trying to keep my hand out of the way in the first pic!



LOL

al

 

[Dennis Sorensen]

I have not had any chambers 'forced sideways' by holding the short dog... magnum cases get pretty 'heavy' towards the end...
This is a 308 chamber...

 

[Charles E]

I have real knowledge to add, just an observation.

Back in the days when anybody could shoot in the Factory Class at Hawks Ridge, Joel Pendergraft got a Savage .300 Win Mag to compete. It was a typical Savage barrel of the late 1990s -- rough.

We went to the range, and as he had other things to work on, I firelapped this barrel for him. We knew there was some risk of pushing the throat forward, so I both cleaned and used the borescope after every firelapping shot. By how shiny things got, I believe you could see where the bullet was bearing on the barrel.

What you'd expect, I suppose. There was a shiny line down the center of each groove, but it wasn't quite as shiny -- or anywhere near as wide -- as the line down the center of lands.

My conclusion was that in the early part of the bullets passage down the barrel, the lands were most important.

FWIW. Anyone got any counter evidence / explanation?

BTW, the corner of the grooves seemed untouched. Makes you wonder about the claims made for different land profiles. Well, one barrel, 20 shots, YMMV

 

[Sam Duke]

Quote " Thanks Jerry, I finally see what you're saying.... I think. You're saying that the true story is told in the GROOVES not up on top of the lands. I can't disagree with your logic."

Where does the reamer pilot run?

Sam