Barrel Threading
- Thread starter yoteslayer77
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Originally Posted By: jpx2rkI'm going to need at least 3 rifles threaded in the near future, so can someone point me in the right direction of what questions to ask and the correct answers I should be getting. For example, what does "thread the barrel between centers" mean ? TIA
I like to ask for references, I want to see what work the machinist has done in the past so that I can ask the end users what the results were. The proof is on the paper. Word of mouth from reliable shooters can help you to find a good machinist. Then you need to make sure that they know how to machine a barrel and that they have done it.
A center is a tapered tool, usually tapered to 60 degrees, that allows the piece to be more accurately held and spun by the lathe. Some machinists just use the chuck to told the barrel, but their chucks can be off, although with a high quality lathe that is not as likely, but the center of the barrel might also be off. I have seen some machinists try to "center" the barrel by using the outside diameter of the barrel. That is where things break down and like all professions you have good machinists and you have bad machinists. If a machinist tries to use the OD to thread from, you will end up with tragic problems like baffle strikes, because the barrel center line and the OD may not be perfectly parallel and may intersect. I have worked alongside many guys who called themselves "machinist" who were much like guys that call themselves "refuse engineers" because they toss garbage. Running a machine does not make you a machinist.
A good professional machinist will place the barrel in a center to help them to find the true "center" of the barrel. Our guys also will measure the individual lands and grooves to make sure that they are the same length when they were finished. This helps the gases to vent equally and will help to minimize thrust on the bullet caused by gas jetting. This is a key to barrel crowning.
Many times the barrels that come out of factories can be hit or miss. A top quality barrel is usually quite accurately machined. But in the shooting world, people sometimes have to buy as much gun as they can afford, and the quality control on the barrels can vary greatly. Many high end barrels look for end to end run out of .001-.003 when the barrel stock is selected and then they check again once the barrel is rifle drilled and then again when it is rifled, and again once the barrel is chambered. Different manufacturers have different procedures and proprietary methods they use to tighten up these specs as much as they can such as honing before and after processes, etc. These things all cost time and money. So some companies will accept higher tolerances and the end results of lower accuracy.
So it is not too hard for a hobbyist with a cheap lathe to quickly destroy all the hard work that went into making a barrel. Having worked with companies like Lilja, ER Shaw, Kreiger, Bartlein, Lothar Walter, McGowen I have seen just how varied the barrels can be. There's good then there's good. But you don't want to see a $300-$800 barrel ruined by someone who doesn't know what they are doing.
Hope that helps.
I like to ask for references, I want to see what work the machinist has done in the past so that I can ask the end users what the results were. The proof is on the paper. Word of mouth from reliable shooters can help you to find a good machinist. Then you need to make sure that they know how to machine a barrel and that they have done it.
A center is a tapered tool, usually tapered to 60 degrees, that allows the piece to be more accurately held and spun by the lathe. Some machinists just use the chuck to told the barrel, but their chucks can be off, although with a high quality lathe that is not as likely, but the center of the barrel might also be off. I have seen some machinists try to "center" the barrel by using the outside diameter of the barrel. That is where things break down and like all professions you have good machinists and you have bad machinists. If a machinist tries to use the OD to thread from, you will end up with tragic problems like baffle strikes, because the barrel center line and the OD may not be perfectly parallel and may intersect. I have worked alongside many guys who called themselves "machinist" who were much like guys that call themselves "refuse engineers" because they toss garbage. Running a machine does not make you a machinist.
A good professional machinist will place the barrel in a center to help them to find the true "center" of the barrel. Our guys also will measure the individual lands and grooves to make sure that they are the same length when they were finished. This helps the gases to vent equally and will help to minimize thrust on the bullet caused by gas jetting. This is a key to barrel crowning.
Many times the barrels that come out of factories can be hit or miss. A top quality barrel is usually quite accurately machined. But in the shooting world, people sometimes have to buy as much gun as they can afford, and the quality control on the barrels can vary greatly. Many high end barrels look for end to end run out of .001-.003 when the barrel stock is selected and then they check again once the barrel is rifle drilled and then again when it is rifled, and again once the barrel is chambered. Different manufacturers have different procedures and proprietary methods they use to tighten up these specs as much as they can such as honing before and after processes, etc. These things all cost time and money. So some companies will accept higher tolerances and the end results of lower accuracy.
So it is not too hard for a hobbyist with a cheap lathe to quickly destroy all the hard work that went into making a barrel. Having worked with companies like Lilja, ER Shaw, Kreiger, Bartlein, Lothar Walter, McGowen I have seen just how varied the barrels can be. There's good then there's good. But you don't want to see a $300-$800 barrel ruined by someone who doesn't know what they are doing.
Hope that helps.
FWIW... the small caliber stuff is extra bad on the deep hole drilling. It's typical - not unusual - but the norm, for a .17 bore from one of the top makers to be hella crooked and not have much a relationship to the OD of the barrel.
I had several top shelf .17 barrels chopped and threaded in my last batch and asked to have the stubs saved for me to weigh and satisfy my various curiosities with. Bore was of course centered at the old muzzle on them, but it was nowhere close to centered on the back end of any of those stubs.
Guy chucks one of those barrels up and indicates off the OD, or even just the bore right at the muzzle, bad ju-ju gonna ensue...
So ask them how they setup, and how, very specifically how and using exactly what, they are going to indicate. And what the plan is when nothing lines up with anything. Because that is often that actual case with small calibers of any make and factory bores of any caliber. Everybody has a plan until crap doesn't go the way it was supposed to. This stuff has a tendency to not go the way it was supposed to. The real craftsmen thrive on solving these problems. The pipe fitters are scarcely even aware the problem exists.
- DAA
I had several top shelf .17 barrels chopped and threaded in my last batch and asked to have the stubs saved for me to weigh and satisfy my various curiosities with. Bore was of course centered at the old muzzle on them, but it was nowhere close to centered on the back end of any of those stubs.
Guy chucks one of those barrels up and indicates off the OD, or even just the bore right at the muzzle, bad ju-ju gonna ensue...
So ask them how they setup, and how, very specifically how and using exactly what, they are going to indicate. And what the plan is when nothing lines up with anything. Because that is often that actual case with small calibers of any make and factory bores of any caliber. Everybody has a plan until crap doesn't go the way it was supposed to. This stuff has a tendency to not go the way it was supposed to. The real craftsmen thrive on solving these problems. The pipe fitters are scarcely even aware the problem exists.
- DAA