BAT 25 Degree Cone Depth

Joe said:
How deep is the 25 degree cone from the edge of a 6BR chamber?
Click to expand...

Joe,

I'm not a pro gunsmith but have done a number of BATs and others that have the cone bolt. I've found that it is rather easy to thread the shank and then do the cone in the barrel but hold it obviously shallow. I then screw the receiver on, with the bolt closed, and allow the bolt face to touch the cone. At that time, I measure the space between the receiver and the shoulder on the barrel. That distance plus about .005 is how much more I must remove from the cone.
I have a dial indicator setup to show where the carriage was when I made the cut before trying the receiver/bolt.
Harder to describe than it is to do, I think.

There was an article in PS a few years ago on making tooling that allowed one to establish cone depth but I never saw a reason to go to that extreme.

Jay, Idaho
 
Butch

Without having to dodge barbs from a few action makers, I would give this advice. Treat every action as an individule.

I have been doing quite a few Pandas as of late, and while they are pretty close, I did one a few weeks back that was at least .008 different than some previous.

Also, I built myself a new Rifle a while back, and I finally set the bolt up and re-cut the cone to match the one on a similiar action. At least .010 difference.

But this bares repeating. There is only one reason to keep the cone clearance as close as possible without causing any problems. That is to avoid uncovering the solid portion of the case web, which is pretty close in the BR and PPC Case.

Some actions can have quite a bit of cone clearance and still the case supported. Both of my Stiiler Actions have a shallow enough counter bore that what seems like a lot of cone clearance is of no concern. The Farleys, though, have the bolt nose ending at just about the front of the extractor groove, just when you give it about .005, there is already some of the case exposed.

Every Gunsmith should check each action and treat it as an individule........jackie
 
Jay said:
Joe,

I'm not a pro gunsmith but have done a number of BATs and others that have the cone bolt. I've found that it is rather easy to thread the shank and then do the cone in the barrel but hold it obviously shallow. I then screw the receiver on, with the bolt closed, and allow the bolt face to touch the cone. At that time, I measure the space between the receiver and the shoulder on the barrel. That distance plus about .005 is how much more I must remove from the cone.
I have a dial indicator setup to show where the carriage was when I made the cut before trying the receiver/bolt.
Harder to describe than it is to do, I think.

There was an article in PS a few years ago on making tooling that allowed one to establish cone depth but I never saw a reason to go to that extreme.

Jay, Idaho
Click to expand...

Jay,
Lots of actions on BR guns are glued in the stock therefore you can't screw the action on the barrel when it's in the lathe.
 
J. Pendergraft said:
Jay,
Lots of actions on BR guns are glued in the stock therefore you can't screw the action on the barrel when it's in the lathe.
Click to expand...

J.P.,

Thanks for that comment. I don't do anything with the short range BR stuff so I had not thought of that. I do have a Hart action PPC that is glued in but I just figured to break down the epoxy and remove the barreled action if necessary. The Hart uses a Rem style bolt, not coned.
So, there is a need for tooling when dealing with coned bolts and glue ins.

Jay, Idaho
 
The reason I was asking is because the action is glued in and I can't check it without taking the barrel out of the lathe.

I was hoping that someone would have a magic depth on the "Z" axis, in thousandths, after touching off on the edge of a fresh 6BR chamber.

I built my own depth gage/dial indicator tools for measuring the cone on a Panda. (which is 30 degrees)
 
Joe,
All you have to do is make another tool that is 25deg. like your Panda tool. If you think about it, your Panda tool should work.
Butch
 
I'm guessing you don't have an old barrel to gage off of?

You could leave the length safely O/S, trial fit & measure the gap between the receiver and barrel shoulder, then set it back up and take the depth to size.......yep, it sounds like a real pain.

-Dave-:)
 
You're right Butch, my Panda gage should and will work.

I am just trying to get a measurement.......a depth of cut from the end of the barrel tenon........so I can get it right without having to take the barrel out of the spiders, trial fit the cone depth, and risk setting it back up to take a few more though off of the cone.

I have a setting on my gage (for a Panda tenon) that I can cut the cone and measure it right in the lathe without trial fitting. I can hit .005" clearance over the bolt nose without taking the barrel out of the lathe.
 
Joe,
I am out of town and cannot post pics of my tools. Am I to gather that you have a glued in receiver and no old barrel off of it to measure?
Butch
 
Another method...

is to place go gauge in chamber them hold bolt nose against it. May want to have tail stock center gently pushing against it to keep it centered. Measure clearance between breech and bolt cone. This is assuming that your chamber depth is at go. If you don't have the action that you can take measurements from or the bolt it is an iffy proposition at best. As Jackie stated, I too have seen a few that will not be right when cut to specifications. If you copy an older barrel from that particular action, you better be sure that it is right or you might just might be copying someone else mistake.
If you want to really see how much of the web is exposed, just cross section the web area of a Lapua case and insert it into your completed work. Some actions will surprise you as to how close you are too exposing the entire web. Not a lot of room for error!
Regards...Herb Coates
 
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