Off Center throat question...

[eww1350]

I chambered a Hart barrel recently and had an odd problem..the lead or throat was longer on one side than the other..I am puzzled how this happened I set up thru the headstock and indicate the barrel at both ends. Then I drill out the excess metal for the chamber, then indicate on the grooves at the area where the lead or throat will be, I then bore out true to the grooves and then cut my tenon and thread it before running the reamer in.
The reamer is held with a PTG floating reamer holder with the tightest fit pilot bushing for the caliber.
How can the reamer cut the throat longer on one side when it has the ability to float and align with the bore..


Eddie in Texas

 

[savagedasher]

I chambered a Hart barrel recently and had an odd problem..the lead or throat was longer on one side than the other..I am puzzled how this happened I set up thru the headstock and indicate the barrel at both ends. Then I drill out the excess metal for the chamber, then indicate on the grooves at the area where the lead or throat will be, I then bore out true to the grooves and then cut my tenon and thread it before running the reamer in.
The reamer is held with a PTG floating reamer holder with the tightest fit pilot bushing for the caliber.
How can the reamer cut the throat longer on one side when it has the ability to float and align with the bore..


Eddie in Texas

Did you use a a range rod or similar tool to indicte the true bore off from? Larry

 

[WSnyder]

A land or two may have been "taller" than the others, by centering the bore on the grooves and the pilot following the lands you get an off center throat.

 

[eww1350]

I do not use a range rod, I know the "Gritter's" method but have not used it because of the need to index the muzzle after chambering, also have not seen this problem on the Bartlein and Kriegers..

 

[savagedasher]

I do not use a range rod, I know the "Gritter's" method but have not used it because of the need to index the muzzle after chambering, also have not seen this problem on the Bartlein and Kriegers..

U index off the chamber end . Centering a barrel off the of of the barrel is not the best way of doing. With a range rod and the correct bushing you can dial in the chamber end on the range rod perfect . . The front end may be tuning off center. 100 thousand or more Mark the high spot on the on the crown end and is the high spot go reference for timing Larry

 

[eww1350]

If the floating reamer holder will not let the reamer follow the bore, what is the purpose.?? the PTG reamer holder has lots of axial movement, and is adjustable for torque to prevent chatter..

 

[Dusty Stevens]

Try to not pre bore it and see what it does. When you prebore your setup is about twice as critical

 

[eww1350]

OK, one more observation to consider...Jackie Schmit uses a lathe that has a 60 degree center inside the headstock on which he put the crown/muzzle. He uses a adjust true chuck to indicate his barrel breech with a long stem indicator at the chamber throat area.. he then drills, pre-bores and chambers the tenon before threading and headspacing. He uses the tailstock to push the reamer and holds the reamer with a handle device..how in the world can he avoid a off center chamber using his method if you say the ranging rod is the only way to avoid an off center chamber/lead..??

 

[savagedasher]

If the floating reamer holder will not let the reamer follow the bore, what is the purpose.?? the PTG reamer holder has lots of axial movement, and is adjustable for torque to prevent chatter..

The tool holder must be perfect aligned with the bore

OK, one more observation to consider...Jackie Schmit uses a lathe that has a 60 degree center inside the headstock on which he put the crown/muzzle. He uses a adjust true chuck to indicate his barrel breech with a long stem indicator at the chamber throat area.. he then drills, pre-bores and chambers the tenon before threading and headspacing. He uses the tailstock to push the reamer and holds the reamer with a handle device..how in the world can he avoid a off center chamber using his method if you say the ranging rod is the only way to avoid an off center chamber/lead..??

He has the barrel center off the bore that is the correct way . Larry

 

[eww1350]

The tool holder must be perfect aligned with the bore

He has the barrel center off the bore that is the correct way . Larry

Larry, if you read my original post I do exactly the same as Jackie, except I indicate inside my muzzle versus using a 60 degree center to align it...the breech end is done identically except I use a floating reamer holder..

 

[savagedasher]

Larry, if you read my original post I do exactly the same as Jackie, except I indicate inside my muzzle versus using a 60 degree center to align it...the breech end is done identically except I use a floating reamer holder..

How far did you drill?

 

[eww1350]

I drill about .050" short of the shoulder/body junction, I then indicate on the grooves with a long stem indicator in the area where the chamber throat will be...then I bore true to the last indicator reading so the reamer will run true to the bore and not be influenced by the drilled hole. I am wondering if the real issue is the floating reamer holder..??

 

[savagedasher]

I drill about .050" short of the shoulder/body junction, I then indicate on the grooves with a long stem indicator in the area where the chamber throat will be...then I bore true to the last indicator reading so the reamer will run true to the bore and not be influenced by the drilled hole. I am wondering if the real issue is the floating reamer holder..??

Drilling that deep is without using a boreing bar is I wouldn't do . Larry

 

[dmoran]

Drilling that deep is without using a boreing bar is I wouldn't do . Larry

Larry -
Do you yourself chamber barrels?
Donovan

 

[boltfluter]

As W. Snyder mentioned your button rides on the lands and you need to indicate the same way. Your reamer holder probably only floats radially. I use a Bald Eagle that floats radically and axially and has clearance on the back end to float freely. I also only indicate the end that I am working on in. In my experience dialing in both ends at once just bends the barrel. This is just what has worked for me personally. Many different ways to chamber a barrel. Good luck and hope this makes sense.

Regards, Paul

www.boltfluting.com

 

[Tozguy]

A land or two may have been "taller" than the others, by centering the bore on the grooves and the pilot following the lands you get an off center throat.

When using a long reach indicator does it show if there is a difference in the height of the lands?
I don't use that method but I would like to know what differences long reach indicators can reliably pick up.

 

[Roeder]

A land or two may have been "taller" than the others, by centering the bore on the grooves and the pilot following the lands you get an off center throat.

I would put it that one or 2 grooves are likely deeper than the others. The tight pilot keeps the reamer cutting concentric to the bore diameter which may not be exactly concentric to the groove diameter. I guess I'm saying about the same thing as WSnyder.

This is fairly common with button rifled barrels. Some make it a point to use a loose fitting pilot and rely on the pre bored chamber to keep the reamer centered concentric to the groove diameter. I doubt that your floating reamer holder is a factor with this issue.

 

[billlarson]

I chambered a Hart barrel recently and had an odd problem..the lead or throat was longer on one side than the other..I am puzzled how this happened I set up thru the headstock and indicate the barrel at both ends. Then I drill out the excess metal for the chamber, then indicate on the grooves at the area where the lead or throat will be, I then bore out true to the grooves and then cut my tenon and thread it before running the reamer in.
The reamer is held with a PTG floating reamer holder with the tightest fit pilot bushing for the caliber.
How can the reamer cut the throat longer on one side when it has the ability to float and align with the bore..


Eddie in Texas

I would slug the bore...trying to determine if you got a high land.
Thru the headstock with spider can induce a bow in the tube..... IF...... your chucking with jaws instead of some type of gimbel and you put too much pressure on the muzzle end with the spider...
bill

 

[butchlambert]

You can sure tell who has successfully chambered barrels by reading some of the answers. Be careful Eddie, I think you should be able to separate the wheat from the chaff.

 

[eww1350]

I will Butch