Bolt Cone to Cone Breech Clearance, How Much?

[Dennis_in_VA]

I'm getting ready to put a barrel on a Bat MB and I'm ready to put the tool to the steel.

My question for those of you more experienced than myself is:

How much clearance between the bolt and the breech is necessary and how do you go about checking this to make sure that you have what you THINK you have?

How much is too much or too little gap?

Thanks in advance for your input.

 

[Wayne Shaw]

Thread the tenon long, start cutting the cone, then screw the action on with the bolt in and locked. Once it hits the tenon, measure the gap between the shoulder and action. When you get closer, use feeler gauges to measure. Then give .005 to .007 clearance.

You can make measuring jigs to do this too, but the above will get it done.

 

[Dennis_in_VA]

Thanks Wayne.
That makes way more sense to me that some of the "Guessing" methods being dished out on these videos.

 

[Wayne Shaw]

No guessing here. Once you do one barrel with action in hand, with the proper measuring jigs, you can duplicate every barrel from then on.

 

[JerrySharrett]

Kelblys reccomended 0.010" one time when I ask George Sr. Anything much less you stand a chance of a powder kernel stopping the bolt from closing. most stick powder kernels are in the 1/32" thickness range but will compress some.

Much more than about 0.020" you are getting close to the thinner part of the brass case and under an extreme pressure situation could get a case rupture.

 

[pbike]

other ideas

There is a very interesting article in the "Benchrest Primer" on this very subject (Gap Space)... the article was authored by the Late Great Phil Sauer.


I once watched a very famous gunsmith use a small soft piece of lead, (Pb), and he put it on the front of the bolt with the rifle pointed up. He then closed the bolt to crush the lead. After opening the action and retriving the lead he measured it's thickness. .007" is what I remember.


Paul

 

[Ken Worth]

There is a very interesting article in the "Benchrest Primer" on this very subject (Gap Space)... the article was authored by the Late Great Phil Sauer.


I once watched a very famous gunsmith use a small soft piece of lead, (Pb), and he put it on the front of the bolt with the rifle pointed up. He then closed the bolt to crush the lead. After opening the action and retriving the lead he measured it's thickness. .007" is what I remember.


Paul

Paul, is that article in the old Benchrest Primer. Mine is on loan.

 

[pbike]

Is there a new "Benchrest Primer"? Must be the Old one, It's the only one I know of and I've had it for at least ten years.

Looks like page 156 in the old one. By the way, A number of years ago a fella sent me this "table of contents", since the Benchrest Primer doesn't have one. A book without a Table of contents, must be a PS thing.

Paul