Bolt Cone to Cone Breech Clearance, How Much?

[Dennis_in_VA]

I'm getting 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.

 

[Preacher]

I like .005 on mine.. but I keep the action really clean...
Cut it on the short side and screw it all together with the bolt in place and check the distance between the action and the barrel shoulder and remove that plus .005 and that will give you what you need... it works for me anyways...
To little clearance and the bolt won't close..
To much clearance and it will leave a lot of the cartridge unsupported...

 

[Cheechako]

What Preacher said. He knows what he's talking about.

I've gone as much as .010" on some of mine but there is really no reason for that much gap if you keep your rifle clean (and you should!).

If you need a reason to justify that $20,000 lathe, you can make yourself a gauge with an attached dial indicator and get it right down to a XXXX hair every time, first time. :

A quick and dirty way to measure the gap is to close the bolt with a short piece of soft solder between the bolt and barrel. It takes three hands to do it the first time but you can then measure the thickness of the solder after it's been compressed.

ray

 

[Dennis_in_VA]

Thanks Preacher, I will try that on my next test run.
I have already threaded a dummy stub to check things out.
I took a piece of lead solder and stuck it to the bolt with some grease and cammed it shut.
I had .020" clearance. I picked this trick up from a post I saw a while ago.
I like the way Preacher said to do it.
Thanks. My day is not a total waste because I learned something new today.

I will post up when I get the real one threaded on .

 

[Robert]

I'm getting 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.

Dennis,

As Preacher says, .005 to .008 is OK.

The clearance can be easily controlled by fixing with grease on the bolt cone a small piece of thin lead wire (old fuse wire), closing the bolt on the tightened barrel, and miking the crushed lead wire to accurately determine the gap size.

In some actions, there could be an interference issue with the extractor front against the barrel cone. This is to be corrected when possible by adjusting the extractor front, not in increasing the clearance.

R.G.C

 

[tdking]

Preacher, shouldn't that be the gap between the action and shoulder MINUS 0.005" to give you a 0.005" gap?

Theron

 

[spclark]

Plastigauge?

http://www.plastigaugeusa.com/how.html

A warmed chunk of jewelers' wax?

http://www.progresstool.com/pd_wizard_wax.cfm

 

[holstil]

Screw the action on the barrel with th bolt in it when you get close. Use feeler gauges to detemine how much shoulder to take off. You can then do the same thing with the go gauge or brass for chambering depth.
Jim

 

[blawton]

On a cone bolt anything between .005 and .015 will work just fine for ya.

 

[butchlambert]

Dennis,
I'm sure you have the right tools.I do mine at .008. My tool for measuring is pictured. Most of our barrel work is on glueins and you can't screw the barrel into a glue in receiver.

Take your take off barrel and slide your headspace gage into the chamber. Screw the tool on the tenon and after the tool Tightens against the shoulder you can run the thimble of the micro until it bears on the gage. Write that number down. Do the same thing with the little valve like tool. When you are doing your new chamber, cut the chamber to match the readings that you took off your take off barrel. Your headspace and tenon to bolt nose should be exactly the same.
Butch

 

[Rustystud]

About six years ago I had a customer who graduated from Montgomery Gunsmithing School who is a Long Range Prone shooter. He thinks he is a lot smarter than anyone else, not the fought of the school. He had me reabarrel a Neseika Bay Action that had a cone bolt. He demanded that it only have .0015" clearance between the bolt and the action. He went to Camp Perry and was shooting in 100 plus degree weather. With the heat comes expansion. His bolt would not open when the gun got hot. I am a firm believer in .005 minimum in clearance. This is also true with real tight tolerences in headspacing. Heat and a little fouling can also make bolt closure a problem.

Nat Lambeth

 

[shortgrass]

About six years ago I had a customer who graduated from Montgomery Gunsmithing School who is a Long Range Prone shooter. He thinks he is a lot smarter than anyone else, not the fought of the school. He had me reabarrel a Neseika Bay Action that had a cone bolt. He demanded that it only have .0015" clearance between the bolt and the action. He went to Camp Perry and was shooting in 100 plus degree weather. With the heat comes expansion. His bolt would not open when the gun got hot. I am a firm believer in .005 minimum in clearance. This is also true with real tight tolerences in headspacing. Heat and a little fouling can also make bolt closure a problem.

Nat Lambeth

"You might lead a mule to water, but you can't make him drink." " Buy 'um books, sent them to school, then they try to -----------". Seems some show up to the accredited schools with alot of pre-conceived ideas they won't turn loose of.

 

[clowdis]

About six years ago I had a customer who graduated from Montgomery Gunsmithing School who is a Long Range Prone shooter. He thinks he is a lot smarter than anyone else, not the fought of the school. He had me reabarrel a Neseika Bay Action that had a cone bolt. He demanded that it only have .0015" clearance between the bolt and the action. He went to Camp Perry and was shooting in 100 plus degree weather. With the heat comes expansion. His bolt would not open when the gun got hot. I am a firm believer in .005 minimum in clearance. This is also true with real tight tolerences in headspacing. Heat and a little fouling can also make bolt closure a problem.

Nat Lambeth

Bet I know exactly who that was