Gene beggs on chambering

Gene Beggs said:
PG

Yours is an excellent question and one that needs to be discussed. Like Alinwa said, never be ashamed to ask a question. I wrote you a response last night but was so tired, I accidentally deleted it instead of posting it. I just called it a night a went to bed. Sorry.

Your question will be discussed and I'll add something in my post number one of this thread about it. My post number one was just an opener. It will be added to and revised many times after we get feedback from others. There's a lot of expertise here on BR Central. This will be an ongoing, informative thread, I assure you.
Click to expand...

Thanks Gene. This is really intersting stuff.
I look forward to reading more. As you had stated at the beginning, this is an ongoing discussion subject to addition and revision.
A number of members have replied to my question (thanks guys) and some say they drill out the excess material before reaming.

That makes me question another item.
When you drill out the barrel to remove excess material before applying that expensive reamer.... How do you maintain the 6mm pilot hole?
I know when I drill out barstock on my South Bend the hole will wander off center very quickly.
Now that does not concern me very much as I am going to ream it to final size later. However, how can I use the pilot on the reamer if I have already drilled out the material with a drill bit?
Without a pilot the reamer will drift off center quicker than a drill bit I would think.
These are just a few of the questions I have trying to get a grasp on how this operation is done correctly.
Thanks........ pg
 
piniongear said:
Thanks Gene. That makes me question another item.
When you drill out the barrel to remove excess material before applying that expensive reamer.... How do you maintain the 6mm pilot hole?
IThanks........ pg
Click to expand...
Predrilling and boring material out of the body of a chamber is common among many gunsmiths. Just use a sharp twist drill that is slightly smaller than the finished chamber would be at the shoulder. I usually use a drill about 1/32" smaller. Drill to just short of the body/shoulder intersection keeping in mind your twist drill probably does not have the same point angle as your cartridge.

Then take a couple of light boring cuts of just a few thousants per side (say 0.005-0.008" or so) stopping short of the drilled hole shoulder. This straight bored section will accurately guide the reamer to start it concentric to the bore if you properly indicated the bore. If it is a long chamber, the reamer pilot may not pick up on the barrel bore at first but the bored hole will act as a pilot until then.

Come to think of it I can not remember ever prebore/drilling that the pilot did not engage first before the reamer body started cutting.
 
JerrySharrett said:
If it is a long chamber, the reamer pilot may not pick up on the barrel bore at first but the bored hole will act as a pilot until then.
Come to think of it I can not remember ever prebore/drilling that the pilot did not engage first before the reamer body started cutting.
Click to expand...

Thanks Jerry. That is what I wanted to know.
pg
 
Survived Thanksgiving

Now,,, back to work.

We have had some great feedback on this thread. As you can see, there are many things to consider. Not only are there basically two different methods of chambering; i.e., thru the headstock and in the steady rest, there are also three different schools of thought on what Jerry Sharett refers to as, "Where The Rubber Meets The Road" or where the bullet enters the bore. Whether you chamber in the headstock or the steady rest, you have to deal with this pesky little detail and it's all due to one undeniable fact; the bores are not perfectly straight. :eek:

Now don't get me wrong; even though very few bores, if any, are perfectly straight, most of them are pretty darn close. So close in fact that I believe most match grade barrel blanks from any of the top barrel makers can be made to shoot competitively if installed properly.

METHOD ONE

This school of thought holds that there are three points along the barrel that must be in line with each other when the chamber is finished; the crown, the leade, and the aft end of the chamber. This method of chambering is done thru-headstock.

It's easy to get the muzzle end of the bore running true and by using the proper dial indicator, one can get the bore running true at the point where the leade will be located but if the bore is not perfectly straight the aft end will not be lined up with the other two points. The only way this can be achieved is by predrilling the chamber and taper boring with a small boring bar before reaming. Maybe this is the best way to do it but I'm not convinced. The problem I see with this method is that if the bore is not perfectly straight, you are bending the centerline of the chamber off axis and the bullet is introduced to the bore crooked. In my opinion, this is not the way to do it.


METHOD TWO

Another school of thought holds that the muzzle is only a handle to be used in lining up the aft end of the bore where the chamber will be. This method is also done thru-the-headstock. The muzzle is held in a spider and with the use of a range rod or Grizzly rod, the first couple of inches of the bore is lined up before chambering. The theory being to let the muzzle wander where it wants as long as the first couple of inches where the chamber will be are lined up. Proponents of this method believe the bullet enters the bore straighter and I tend to agree. Gordy Gritters demonstrates this method in his video, "Chambering a Championship Barrel." He also emphasizes the importance of indexing and places muzzle runout pointed up in the twelve o'clock position.


METHOD THREE

This is the method I use and it is done in the steady rest. I feel it is not only the best way but also the most user friendly method. I've tried them all and I think this is it. It can also be done in most any lathe regardless of spindle ID. The method is described in detail in post number one.

Gene Beggs
 
A common mistaken belief is the bore is curved in a barrel. If you can picture how a barrel is drilled, you can see that ain't what's happening. Running an indicator rod in a bore isn't going to straighten it. You need to remember if you have one with an excessive amount of runout, send it back. Think about this. If you indicate the groove at the leade area and taper bore to that point, you understand that I mean not running the boring bar to that point, just boring toward that measured area. If you have a loose fitting bushing the reamer will follow the taper bored hole and the throat will be coaxial with the indicated leade. Do you think the barrel will make a sharp turn in front of your reamed chamber, I think not! If you have an indicator that will reach indicate beyond the leade and see how much it is off.
Most people on this forum have no clue how much .001 is let alone .0001. This chambering stuff has been discussed many times on all the forums and winning rifles have been chambered several different ways. Choose your own method. The reason I chamber in the headstock is you are working with one setup and it is true to the lathes spindle. It takes less than 2 hours to do a top notch job. You don't have to take the barrel in and out while you are doing your machine work. That means no stack of tolerance.
Butch
 
"Most people on this forum have no clue how much .001 is let alone .0001" I have been thinking the same thing. I am very intrested in chambering a rifle. I have never done it or seen it done. I do however know what .001 is as well as .0001. There are very few who can measure to the .0001. Example If you have 5 blocks of steel ground to diffrent thickness have 5 seasoned machinist measure and write down the measurement to the .0001. Now mix them up and re measure you will find it is very hard to measure to the .0001 and most will measure the same block and get two difftent numbers. "A common mistaken belief is the bore is curved in a barrel" .I do feel the bore is not straight. I feel it is bowed. Not here to argue just want to learn.
 
Mr Dotson
I will agree that nothing is perfect. Do you know how barrels are drilled? Do you have any idea how far they"bow"? I'm certainly not trying to give you a hard time, but it is hard for a person to make a decision on something like this without knowing all the variables. I am here to help you in any way that I can.
Butch
 
Butch Lambert said:
Mr Dotson
I will agree that nothing is perfect. Do you know how barrels are drilled? Do you have any idea how far they"bow"? I'm certainly not trying to give you a hard time, but it is hard for a person to make a decision on something like this without knowing all the variables. I am here to help you in any way that I can.
Butch
Click to expand...
answer to number 1 No I think they use a gun drill? how far they bow? No Idea. forget about he hard time thing I am here to learn so I ask questions
 
Since I have a South Bend 10K lathe, the question of boring at the headstock or at the tail end using a steady rest is one that I do not have to answer.
My lathe has already answered the question for me.
Unless I use a very lightweight barrel (less than 3/4 inch D) it is not going to go through the spindle on a 10K.
Additionally, if the barrel length is a full 26 inches I may not have the bed length on my 3-1/2 ft lathe to do it that way either.
I am currently under the impression it takes a 4-1/2 ft bed to do this with enough room.
Anyone have experience with doing a barrel job on a 3-1/2 ft 10K?
pg
 
Some thoughts

In past times in a Kodak machine shop where there were many high dollar machine tools and nearly 300 well educated and trained machinists we had several applications that used gun drills. One job that comes to mind was a yarn winding shaft that had a 1/8" hole through end-to-end on this SAE4140 shaft that was 25" long. We found that if we rotated the workpiece as well as the gun drill we got a much straighter hole. Hole straightness was not the primary consideration since this passage was for compressed air. A straight hole, however, was desired to keep the gun drill from wandering off and breaking the drill as it would be pinched as the hole wandered off center. Many rifle barrel drilling operations do not rotate both the workpiece and the drill.

As to how crooked the hole is and how it effects accuracy, a few years ago I sectioned a barrel that looked really bad when it was rotated. Turned out that the worst place I could find was a difference of 0.007" out of center (0.014" TIR) measuring from the OD to the ID. This was in a spot about 7" from the blank muzzle. Would/could a drill wander that much just starting the hole? I don't know. I don't even know if the the barrel drilling process takes place always from the same end. i.e. is the drill starting end always maintained to be at the breech end??

(I use 29" blanks as stocked by Lester Bruno. This allows me to cut as much as 8" off the muzzle end blank and still have a 21-3/4" finished barrel at a finish weight of 5# 4 oz. Using this same "Bruno Medium", as he calls it, I can also end up with a 22 1/2" barrel at 4# 12 oz as another extreme.)

Using this worse case example and setting up a barrel and dialing in at the chamber base, then assuming half that error, 0.0035" runout where the leade/freebore merges with the barrel bore. Would you expect a barrel with that much offset to shoot great? I think not.

I have not found a barrel blank with enough crook that by indicating the freebore/leade intersection and preboring that the "cone" appeared to be off-center enough to be visible with a borescope. I have always moved the indicating stylus tip to the base (breech) and checked that runout. I have, on occasion, found a runout of 0.0025"-0.003" TIR while the freebore/leade area was dialed in as close as I could measure with an Interapid indicator.
 
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Most interesting, jerry

When Harold Broughton was making barrels, I was fortunate to be there one day when he was drilling blanks. Harold said he could drill the hole much faster but felt it was more likely to stay straight if he fed the gun drill slower. In his machine, the gun drill bit did not rotate but the barrel itself was really turning. I don't remember him saying what RPM he was using but the barrel blank was really humming. Cutting oil and chips were just boiling out the aft end of the blank.

After the hole was drilled, Harold placed the blank in another machine which pulled a reamer thru while the barrel rotated. We were talking about how straight the hole was and he said, "It's not TOO crooked or that reamer wouldn't go thru there without breaking."
 
Gene Beggs said:
When Harold Broughton was making barrels, I was fortunate to be there one day when he was drilling blanks. Harold said he could drill the hole much faster but felt it was more likely to stay straight if he fed the gun drill slower. In his machine, the gun drill bit did not rotate but the barrel itself was really turning. I don't remember him saying what RPM he was using but the barrel blank was really humming. Cutting oil and chips were just boiling out the aft end of the blank.

After the hole was drilled, Harold placed the blank in another machine which pulled a reamer thru while the barrel rotated. We were talking about how straight the hole was and he said, "It's not TOO crooked or that reamer wouldn't go thru there without breaking."
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I don't have much experience making barrels but I made one under the supervison of Bill Prator in Trinidad, Colorado 44 years ago on his equipment in his shop at home. Bill was an instructor the the gunsmithing college and he offered some students a little extra 'teaching'.

The drilling process took about 30 minutes... the barrel was spun at very high revs and the drill was fed very slowly with a continuous oil flow clearing chips. I don't remember what controlled the feed of the drill, it was not mechanical.

On reaming he also said , maybe not in the exact same words but I understood, "It's not TOO crooked or that reamer wouldn't go thru there without breaking."

The hole exiting the drilled barrel was usually not far off center, but off slightly was acceptable and indicated the drill may need a little touch up.
 
The different deep hole barrel drilling machines that I have seen turn the barrel. The gun drills are single fluted and have a hole in the nose for high pressure cutting oil. The Pratt&Whitney does move the spinning barrel on the carriage.
Butch
 
Someone once told me that Douglas and Krieger turn the barrel and counter rotate the drill, at different speeds, and the others do not. This was before some of the newer barrel makers came on the scene. Also told me that turning both, as a general rule, tends to produce straighter deep holes.
 
If you ever happen to be in Springfield Massachusetts, Savage Arms conducts factory tours. I took 25 of my shooting club members there last fall. Nothing is 'off limits" you can ask to see anything you want. It was amazingly open door policy.
We saw barrels being drilled on very old Pratt and Whitney deep boring machines. Barrels turn, drill is stationary.

P1020118-vi.jpg


Savage uses button rifling. I was told that all holes have a bit of a curve to them, but if they were excessive, it would damage the button. I wasn't told what "excessive" was.

P1020116-vi.jpg


These are the "buttons"

P1020122-vi.jpg


As many of you know, Savage "straightens' all their barrels before they are chambered.

P1020125-vi.jpg


We all got a chance to look down the bore before and after......Amazing. But once the barrel was made straight, you couldn't detect it with the eye from the exterior. It is extremely minor.

All chambering was done on a vertical machine. Rough chamber, finish chamber, final brush hone. All at low speed with constant flush. These machines are constantly being "tweaked" for best possible performance. Only senior folks operate them. I witnessed Remington chambering barrels one time. Not something you want to see on a full stomach.

P1020129-vi.jpg


The rest of the pictures of the tour are here:

http://public.fotki.com/Rbertalotto/bang!/savage-factory-tour/

Hope this keeps the discussion going!
 
I went on a tour at a small button rifling operation and the over-size blanks were contoured between centers after they were drilled (barrel rotated and drill supported), then reamed and button rifled. The button rifling process was the button was pulled through and rotation was under power, which matched the twist of the button, so that twist was constant. The rifling button was followed with a second smooth button on the same rod to smooth the top on the lands and give a consistent ID between lands. The lubrication during the button rifling process is important to prevent chatter which makes the lands look like railroad tracks. There is quite a difference in button rifled barrel quality and the fouling when used. Most of the factory chambers I've seen through a bore scope don't have concentric throats. I've seen hammer-forged factory barrels that are better than factory button-rifled barrels as well. - nhk
 
 
Finished

Well guys, that's about all I can tell you about it so I guess I'm finished. Hope this helps someone with something. If you have any questions, I'll try to answer them and if I can't I know there are many here who know a lot more about it than I do.

It's beginning to look like I'm going to survive this miserable cold I've been fighting since Thanksgiving, so I'll be back in my shop next week.

Later,

Gene Beggs
 
Gene,

Could you describe how you run the reamer and how you gauge depth of the chamber??

This is the sort of stuff that's hard for the new guy to visualize....... you don't just drive the reamer in "about yeahh" using gtrial and error... ;) ... so could you tell us WHEN to stop the reamer and how you know?

thanks


al
 
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