chambering thru headstock

[coyotechet]

I did a lot of checking of the last three barrels, 1 Hart 5groove 6ppc, 1 Krieger 6Dasher, 1 Proof Research 6x47.

First setup was indicating throat then very breech end of each barrel. Then checked the indicator runout at ½ inch or so in front of the indicated throat.
Second setup was indicating throat then muzzle of each barrel. Then checked the indicator runout at ½ inch or so in front of the indicated throat.

The Hart and Krieger where chambered with the Throat and muzzle setup. The Proof Research Throat and breech set up.

Each time I checked in front of the throat I could not see any differences in the indicator reading between the two setups.
After chambering each of the above three barrels I checked the runout on the free bore, shoulder and at the end of the chamber.
All three barrels indicated zero using Interapid 312-15 indicator (same amount of needle movement if any)

I used the Grizzly rod to first indicate the throat on each setup than double checked the throat with the 312-15 also at the ½ mark. I have found for myself that using the Grizzly rod first REALLY speeds up my time indicating the throat and at ½ inch or so in front.

Chet

 

[Mike Bryant]

Chet, the more barrels you do the quicker you get indicating barrels. I haven’t timed how long it takes me to indicate a barrel in, but I figure 5 minutes or less. That last little bit of tweaking to get the indicator to repeat to the same mark seems to take the longest. I really think when it comes to barrel work most of us tend to over think things. Not that it’s bad to do that, but some things matter some don’t. It seems that I’m always learning when it comes to barreling. I have an easy one to do today chambering a 6 BRX. Then after that it’s going to be a hard one or at least a time consuming one. I’ll have to make some tooling to do it. I wish I’d have talked with Tom Martin more when he was alive as this one was right up his alley as he did these routinely. It’s a .50 BMG on a big McMillan action. My long point Interapid would only reach up about midway of the body of the case. So will build an indicator rod that will let me reach in to the throat area. This barrel is 1.75 in diameter at the breech. Fortunately it tapers down to about 1.35 quickly like a Douglas taper so I’ll be able to get it through my headstock.

 

[Dans40X]

Mike,
DO NOT run breech clearance closer than .015"or barrel heat expansion will bind up the coned bolt nose into the 120 degree included angle of the barrel breech.

Been there...once on one of my McM 50BMG DBM Repeaters.

 

[coyotechet]

50 tms

Hello Mike
Like you it only takes me 5 minutes or less to indicate the barrel in at any point. When using the Grizzly rod even less time and still using the 312-15 to double check the runout. Yes Tom was a 50 BMG man to know. Below is a picture of the 50 cal. Tom Martin Spleical. (6PPC--Tom Martin Speical--50 BMG)
Chet

 

[Mike Bryant]

Mike,
DO NOT run breech clearance closer than .015"or barrel heat expansion will bind up the coned bolt nose into the 120 degree included angle of the barrel breech.

Been there...once on one of my McM 50BMG DBM Repeaters.

Thanks, Dan. I appreciate that.

 

[brickeyee]

Chet, the more barrels you do the quicker you get indicating barrels.

It really is practice that does it.
If I do not do lathe work for even a few months, the time is noticeably longer when I start up again.
A lot comes back after a very few set ups.

I miss having access to some very precise lathes we had for aerospace work.
Laser Interferometers to measure with.
We could polish (and measure) down to fractions of a wavelength of light.

 

[Joel]

Mike,
DO NOT run breech clearance closer than .015"or barrel heat expansion will bind up the coned bolt nose into the 120 degree included angle of the barrel breech.

Been there...once on one of my McM 50BMG DBM Repeaters.

You are correct that you need the clearance but not for the stated reason. Mostly for unburnt powder and brass shavings. On a cone bolt anything between .005 and .015 will work.

The thermal Expansion for metals varies depending on composition but for normal firearm steels it's going to be somewhere around 0.0000053" to 0.0000099" per inch per degree. With a 100 degree increase that is still less than a .001" expansion per inch. Also the bolt lug and face will be at a lower temp than the chamber throat area of the action/barrel. Due to the differences in temperatures of the different areas calculating the clearance change is in not an easy undertaking. While the bolt, receiver and barrel are three pieces they will act as a single piece if the temperature increase is the same for all three piece. In that case the clearance will increase not decrease. It will act the same as if it was a slot or a hole in a solid piece.

 

[alinwa]

........While the bolt, receiver and barrel are three pieces they will act as a single piece if the temperature increase is the same for all three piece. .......

And how on God's EARTH could this happen?

Let's start with, "please define the mechanism which heats the bolt".....

 

[Joel]

And how on God's EARTH could this happen?

Let's start with, "please define the mechanism which heats the bolt".....

Thermal expansion his difficult for lots of folks to understand. It gets even more difficult when the heat source is uneven or one sided. Fortunately using 2D examples to demonstrate what is actually happening is simple. Dimes and quarters are what I normally use but large and small primers are fine. Whatever you chose to use it represents one atom. A dime would represent room temperature and the the quarter would represent an elevated temperature.

Metal expands when heated because an increase in temperature is actually an increase in the vibration of the atoms that compose the metal, and this vibration forces the atoms slightly apart.

I use this visual when people have a have time understanding why at hole in a part gets larger and not smaller when heated. Round, square or rectangular it makes no difference but for this scenario square will work the best. You will need 16 dimes and 16 quarters (or whatever use choose) to build two squares with 5 per side. Build one square with dimes and one square with quarters. Once you do this it is easy to visualize why the ID and the OD both get larger.

It gets more interest in the when the temperature are uneven like in the case of a something like a rifle action. If the temperature increase would be even the action acts no different than round, square or rectangular cutout in a solid pieces.

In the case of a rifle action the bolt, action and barrel are different alloys so the expansion rates will be different so it's not exactly the same as a solid piece but the principles are the same.

With a rifle the firing cartridge provides the heat. The heat is transferred to the barrel first. Since the barrel is in contact to the receiver some of this heat is transfer to the action and the case head also transfer some heat to the bolt face. Since the bolt and barrel are retained by the receiver they respond to heat expansion the same as a solid being heated from one side only.

Combine your dimes and quarters and layout your square with one 1/2 being dimes and one 1/2 being quarters. The ID still gets bigger.

That is not completely accurate representation since the barrel will be hotter and some of the expansion will be towards the bolt face. Some of this heat will transfer to the front of the receiver and portion of the barrel and receiver will be expanding away for them bolt face. The hot spot of the barrel will be the front of the chamber and throat area.

That were this gets complicated since the back of the barrel will be hotter that the receiver perpendicular to the back of the barrel. That will be the only material actually moving towards the bolts face. To even complicate the matter more on a coned breech the cone in the barrel will be expanding so that portion of the expansion will be moving away from the bolt face. Total in a best/worst case it might be possible it get a tenth or two decrease in the bolt face cone clearance.

 

[alinwa]

Thermal expansion his difficult for lots of folks to understand.............

Ohh, isn't that cute.

 

[Joel]

Ohh, isn't that cute.

And how on God's EARTH could this happen?

Let's start with, "please define the mechanism which heats the bolt".....

It's simply stating a fact. Even folks that deal with it in industry have a hard time with it. Most folks have a very hard time with the why the material by a hole is not expanding inwards and making the hole smaller. Do you have anything other than SA comments to contribute?

 

[jackie schmidt]

Thermal expansion his difficult for lots of folks to understand. It gets even more difficult when the heat source is uneven or one sided. Fortunately using 2D examples to demonstrate what is actually happening is simple. Dimes and quarters are what I normally use but large and small primers are fine. Whatever you chose to use it represents one atom. A dime would represent room temperature and the the quarter would represent an elevated temperature.

Metal expands when heated because an increase in temperature is actually an increase in the vibration of the atoms that compose the metal, and this vibration forces the atoms slightly apart.

I use this visual when people have a have time understanding why at hole in a part gets larger and not smaller when heated. Round, square or rectangular it makes no difference but for this scenario square will work the best. You will need 16 dimes and 16 quarters (or whatever use choose) to build two squares with 5 per side. Build one square with dimes and one square with quarters. Once you do this it is easy to visualize why the ID and the OD both get larger.

It gets more interest in the when the temperature are uneven like in the case of a something like a rifle action. If the temperature increase would be even the action acts no different than round, square or rectangular cutout in a solid pieces.

In the case of a rifle action the bolt, action and barrel are different alloys so the expansion rates will be different so it's not exactly the same as a solid piece but the principles are the same.

With a rifle the firing cartridge provides the heat. The heat is transferred to the barrel first. Since the barrel is in contact to the receiver some of this heat is transfer to the action and the case head also transfer some heat to the bolt face. Since the bolt and barrel are retained by the receiver they respond to heat expansion the same as a solid being heated from one side only.

Combine your dimes and quarters and layout your square with one 1/2 being dimes and one 1/2 being quarters. The ID still gets bigger.

That is not completely accurate representation since the barrel will be hotter and some of the expansion will be towards the bolt face. Some of this heat will transfer to the front of the receiver and portion of the barrel and receiver will be expanding away for them bolt face. The hot spot of the barrel will be the front of the chamber and throat area.

That were this gets complicated since the back of the barrel will be hotter that the receiver perpendicular to the back of the barrel. That will be the only material actually moving towards the bolts face. To even complicate the matter more on a coned breech the cone in the barrel will be expanding so that portion of the expansion will be moving away from the bolt face. Total in a best/worst case it might be possible it get a tenth or two decrease in the bolt face cone clearance.

Joel, what you are stating is put into practice in shops such as mine on a weekly, if not sometimes daily basis.

In short, we heat a lot of parts in order to install them, and freeze bushings and pins in order to slip them in place.

I see nothing in your analysis that would contradict what we put in practice. The main thing is that when heating or freezing parts to increase or decrease diameter, it is not only important to arrive at the correct temperature, but also insure that the temperature is distributed evenly in the part.

As for giving a bolt nose sufficient clearance in the counterbore or the cone, I can see no application where the temperature would rise to a level to compromise a .005 clearance fit. All you have to go is take a piece of steel, measure the diameter, and then heat it to where it expands .005 inch. I would challenge anybody to shoot a modern firearm enough times in succession to allow parts to reach this temperature.

And, as you stated, the parts are not independent, heat travels fron one to the other.

Modern rapid fire firearms Usually have some means of bleeding off excess heat so the Mating parts do not experience failure due to over heating.

We will be shrinking on some 8inch ID x 8 3/4 OD x 30 inch long NCB coated liners on a a couple of 8 inch shafts in a couple of days. I should take a video of how we do this so everyone could see just what is involved.

 

[TrxR]

Joel, what you are stating is put into practice in shops such as mine on a weekly, if not sometimes daily basis.

In short, we heat a lot of parts in order to install them, and freeze bushings and pins in order to slip them in place.

I see nothing in your analysis that would contradict what we put in practice. The main thing is that when heating or freezing parts to increase or decrease diameter, it is not only important to arrive at the correct temperature, but also insure that the temperature is distributed evenly in the part.

As for giving a bolt nose sufficient clearance in the counterbore or the cone, I can see no application where the temperature would rise to a level to compromise a .005 clearance fit. All you have to go is take a piece of steel, measure the diameter, and then heat it to where it expands .005 inch. I would challenge anybody to shoot a modern firearm enough times in succession to allow parts to reach this temperature.

And, as you stated, the parts are not independent, heat travels fron one to the other.

Modern rapid fire firearms Usually have some means of bleeding off excess heat so the Mating parts do not experience failure due to over heating.

We will be shrinking on some 8inch ID x 8 3/4 OD x 30 inch long NCB coated liners on a a couple of 8 inch shafts in a couple of days. I should take a video of how we do this so everyone could see just what is involved.

I would think for the heat to get hot enough to change the dimensions of the boltface it would do an awful number on the brass?

Ive used heat expansion and cold to install bearings on shafts or in cases a few times and it takes a fair bit of heat depending on the material so i get the principle .

 

[brickeyee]

It's simply stating a fact. Even folks that deal with it in industry have a hard time with it. Most folks have a very hard time with the why the material by a hole is not expanding inwards and making the hole smaller. Do you have anything other than SA comments to contribute?

A hole EXPANDS as if it was filled with the same material.
That means the hole gets LARGER.

 

[Louis.J]

Jackie I would really enjoy watching a video of the process.

 

[Joel]

A hole EXPANDS as if it was filled with the same material.
That means the hole gets LARGER.

Please reread the statement you commented on below. Than read post #9.

It's simply stating a fact. Even folks that deal with it in industry have a hard time with it. Most folks have a very hard time with the why the material by a hole IS NOT expanding inwards and making the hole smaller.

 

[Joel]

Jackie thanks for the comments. I've always enjoyed reading your posts and your seemingly endless patience to share and be helpful. Too be honest you are a better man than I am. Like you I have been in this business a long time. I started in the mid 70's. During that time I would build match rifles for friends and fellow competitors but precision machining was always my mainstay.

I used to hang out a lot here back in the day when world class smiths used to freely share their knowledge here. Alan Warner and Chad Dixon come to mind. I know there were others also but I am not sure if it was this forum or others. It appears you maybe the only one left. I haven't back read the older posts so if I am slighting any of the truly knowledgeable posters that is not my intent.

Stopped hanging out here when Alan Warner and Chad Dixon stopped posting. At the time Chad Dixon had built the raining 1,000 World Record holding rifle. Chad used somewhat of a different threading and chambering technique. He shared his method and was savaged for using a different methodology by people that probably never barreled a rifle let alone a world record 1,000 yard grouping rifle.

The only thing that appears to have changed here is there is a lot less participation. I wonder why???????

A personnel thanks to you Jackie for hanging in here. As I said you are a better man than I am.

 

[Louis.J]

Jackie is one of the reasons I am on this site I never cease to learn something new from his very informative posts. There are others here that I also feel the same way about and they too are also the reason I enjoy coming to this site. In regards to building match winning rifles there are several here who do exactly that. It's up to who ever is behind the rifles that they build to go out and to set world records and to win matches once their work is done. And there have been several who have the abilities and have done and continue to do just that with what they have built.

 

[alinwa]

Joel,

the simple fact is that some folks have set tolerances too tight and had the barrel tenon expand and touch the bolt head.

I commented because you muddied Dan's post up with your initial statements re "everything heated at the same rate" and other irrelevancies, in an attempt to look knowledgable.

Sorry, in the real world this doesn't happen

sorry to get yore pannies in a wad

sorry to have stood for Dan Armstrong in 'your post'........ contrary to your statement that "Jackie's the only smart one left" I consider Dan to be a valuable asset to this board.

 

[Bob Smeltzer]

Thermal expansion his difficult for lots of folks to understand. It gets even more difficult when the heat source is uneven or one sided. Fortunately using 2D examples to demonstrate what is actually happening is simple. Dimes and quarters are what I normally use but large and small primers are fine. Whatever you chose to use it represents one atom. A dime would represent room temperature and the the quarter would represent an elevated temperature.

Metal expands when heated because an increase in temperature is actually an increase in the vibration of the atoms that compose the metal, and this vibration forces the atoms slightly apart.

I use this visual when people have a have time understanding why at hole in a part gets larger and not smaller when heated. Round, square or rectangular it makes no difference but for this scenario square will work the best. You will need 16 dimes and 16 quarters (or whatever use choose) to build two squares with 5 per side. Build one square with dimes and one square with quarters. Once you do this it is easy to visualize why the ID and the OD both get larger.

It gets more interest in the when the temperature are uneven like in the case of a something like a rifle action. If the temperature increase would be even the action acts no different than round, square or rectangular cutout in a solid pieces.

In the case of a rifle action the bolt, action and barrel are different alloys so the expansion rates will be different so it's not exactly the same as a solid piece but the principles are the same.

With a rifle the firing cartridge provides the heat. The heat is transferred to the barrel first. Since the barrel is in contact to the receiver some of this heat is transfer to the action and the case head also transfer some heat to the bolt face. Since the bolt and barrel are retained by the receiver they respond to heat expansion the same as a solid being heated from one side only.

Combine your dimes and quarters and layout your square with one 1/2 being dimes and one 1/2 being quarters. The ID still gets bigger.

That is not completely accurate representation since the barrel will be hotter and some of the expansion will be towards the bolt face. Some of this heat will transfer to the front of the receiver and portion of the barrel and receiver will be expanding away for them bolt face. The hot spot of the barrel will be the front of the chamber and throat area.

That were this gets complicated since the back of the barrel will be hotter that the receiver perpendicular to the back of the barrel. That will be the only material actually moving towards the bolts face. To even complicate the matter more on a coned breech the cone in the barrel will be expanding so that portion of the expansion will be moving away from the bolt face. Total in a best/worst case it might be possible it get a tenth or two decrease in the bolt face cone clearance.

It has a lot to do with the chem. make up of the material, high carbon, or high silicon, or both will cause more expansion! And then the cooling comes into play if it is cooled with water it will not go down to the same size as air cooling!because of the martinsite!I worked as a roller in a rolling mill for 40 years. When rolling those kind of metals we would see a shrinkage of about 3/16 in per foot of material. But as Jackie said I can not see any gun heating up to those temps. I am talking 1800 to 2000 degrees!