Why dial a rifle bore within .0001"

[Canadian Bushman]

Pretty much all quality gunsmith guarantee to dial a rifle bore in to a few ten thousandths before chambering. Is this really necessary?

With the slop between bore, bushings, and reamer, and the fact that most people use floated reamers on poorly aligned tailstocks, what is to be gained by having a barrel dialed to .0001" instead of .001"?

 

[IdahoCTD]

If your drilling and boring the chamber prior to the reamer touching it then it will make a difference. The reamer will have a much harder time going crooked when it has a straight hole to follow regardless of any slop.

 

[Canadian Bushman]

If your drilling and boring the chamber prior to the reamer touching it then it will make a difference. The reamer will have a much harder time going crooked when it has a straight hole to follow regardless of any slop.

Im not sure i fully understand.

By "straight hole" you mean the rifled bore?

 

[IdahoCTD]

What I do is dial in the barrel and then rough drill most of the chamber out (about .030" under size). Then I come back in with the boring bar and bore the chamber just under the shoulder dimension the full length that it's drilled. Then I enlarge the back of the chamber just enough to get the shoulder of the reamer started into the chamber and the pilot into the bore. Without a flush system you can easily ream the whole portion of the chamber that is bored in one pass. This greatly reduces the amount of time to chamber on big calibers if you don't have a muzzle flush system and it is a lot less wear and tear on your reamers. Unless there is deflection induced by pushing the reamer it has the best chance of going straight this way in my opinion.

 

[J E Custom]

That's a good question.

The reason is simple in my mind. If you don't try to make everything as near perfect you will always wonder if it could be better/More accurate. If I can set the barrel up and not even have .0001 thousandths run out on the bore I will still try to reduce the movement in the dial indicator to less if I can.

If I could I would use .00001 indicators but with the machine that I have it would be almost impossible to do but I would still try.

You are correct about other aspects of the set up. If the tail stock is not true and dialed in and the reamer bushing is a poor fit, It wont make much difference. But setting everything up correctly
is every good smiths obligation.

You may not be able to achieve .0001 accuracy in every faze of a build but you must try. after all, perfect is best and less than perfect is still less.

I have modified my process many times in order to improve the accuracy and quality consistency.
I am also always looking for a better way to do something (Not a short cut). I consider myself a craftsman and a good craftsman never excepts less than his best and never stops trying to improve.

So the long and the short of it is, set everything to .00000 if you can and you will never be sorry.

Just my opinion

J E CUSTOM

 

[lazylabs]

I agree that if you can make it better then why not try, but. With all these good points we then take all these pieces and put a loaded round in.... Crank up the pressure to turn the bullet into a piece of goo that pretty much conforms to any shape... I also think we put a ton on time/effort/money to get from a 1/4" gun to a 1/8" gun and can't show the improvement in field situations.

That said... Give me a Dead nuts gun if you can, the miss is my fault!

 

[Canadian Bushman]

JE,
Thats the answer i was hoping for, and the only reason i have to try to get bores dialed closer each time i indicate a barrel. I personally dont think it makes much if any difference, but if i can get it closer why not. I usually keep trying until i start to go backwards.

Now to put things in a different perspective.
If you could get 6" of the bore running under .0002" and the muzzle running out .015" or 12" of the bore running under .0005" and the muzzle running out .01" which scenario would you choose?

 

[Garycrow]

Because tolerances stack and .0001" here then .0001" there adds up. While it's true that .0001" in one place might not make any difference in a sporter weight rifle, it shows a lackadaisical attitude in general on the part of the gunsmith if he accepts that. I don't want a gunsmith with a lackadaisical attitude, I want and am paying for perfection. That's why I use the best barrels and best gunsmiths I can find. If I was OK with a rifle with loose tolerances I'd stick with a factory rifle and save my money.

The minute I hear a gunsmith say something like "it's only a sporter, it won't matter" or "a shaw is just as good as a bartlein for a sporter" then I scratch him off my list. I want him to treat my rifle no differently than a BR rifle.

 

[SidecarFlip]

That's a good question.

The reason is simple in my mind. If you don't try to make everything as near perfect you will always wonder if it could be better/More accurate. If I can set the barrel up and not even have .0001 thousandths run out on the bore I will still try to reduce the movement in the dial indicator to less if I can.

If I could I would use .00001 indicators but with the machine that I have it would be almost impossible to do but I would still try.

You are correct about other aspects of the set up. If the tail stock is not true and dialed in and the reamer bushing is a poor fit, It wont make much difference. But setting everything up correctly
is every good smiths obligation.

You may not be able to achieve .0001 accuracy in every faze of a build but you must try. after all, perfect is best and less than perfect is still less.

I have modified my process many times in order to improve the accuracy and quality consistency.
I am also always looking for a better way to do something (Not a short cut). I consider myself a craftsman and a good craftsman never excepts less than his best and never stops trying to improve.

So the long and the short of it is, set everything to .00000 if you can and you will never be sorry.

Just my opinion

J E CUSTOM

As a machine shop owner and Journeyman tool and die maker, I own numerous lathes, both manual and CNC and for practical purposes, no lathe with the exception of a second operation toolroom lathe, is capable of holding 1 ten thousandths of an inch.

It's impossible simply because the TIR of the spindle precludes that. The only way a spindle (the headstock end( can hold 0.0001 is if the bearings are Class 5 and 99% of machines sold for general use, aren't. Secondly, 1 tenth is entirely dependent on factors such as temperature of the workpiece and tool deflection.

Anyone who claims they are holding 1 tenth accuracy in a shop enviroment without very special considerations is simply FOS.

Besides, most laymen can't measure 1/10th accurately anyway, tailstock alignment or not, floating reamer or not. Not gonna happen.

 

[WapitiBob]

This might get interesting.

 

[shortgrass]

As a machine shop owner and Journeyman tool and die maker, I own numerous lathes, both manual and CNC and for practical purposes, no lathe with the exception of a second operation toolroom lathe, is capable of holding 1 ten thousandths of an inch.

It's impossible simply because the TIR of the spindle precludes that. The only way a spindle (the headstock end( can hold 0.0001 is if the bearings are Class 5 and 99% of machines sold for general use, aren't. Secondly, 1 tenth is entirely dependent on factors such as temperature of the workpiece and tool deflection.

Anyone who claims they are holding 1 tenth accuracy in a shop enviroment without very special considerations is simply FOS.

Besides, most laymen can't measure 1/10th accurately anyway, tailstock alignment or not, floating reamer or not. Not gonna happen.

Flip is correct. You've got that .0001" slack in your spindle bearings, maybe more. Those TR lathes that are capable are beyond the financial reach of all but those with the deepest pockets. The dials on the handles of most tool & cutter grinders, and surface rinders are graduated in .0005. Takes a very controlled environment to even be able to measure below a 1/2 thou accurately/repeatably (temp, humidity, etc. True "gauge rooms" are always in an isolated, climate controlled room). I've worked in the machining industry since 1974,,,,, there's no perfect, but, we keep striving for it when doing barrel work.

 

[Canadian Bushman]

Thats kinda what brought me to ask this question. I have an old b&s indicator i got from my dad thats really sensitive and i dialed in a bore on a barrel i was getting ready to cut, then got off for the night. Mind you after ive been running the machine for a few hours.

When i left i had a 4-6 inch section running dead nuts and about a 10" section inside .0005" and could just about bury the rod and never cross .001".

Came back the next day to a cold machine and the bore was everywhere. .0005" at the closest and .0015 almost .002 across the length of the rod.

The best lathe spindle i ever had was a hardinge hlv just after the spindle was rebuilt and ground. It ran a legitamate .0002 all day. First and last machine i ran that could do that. Now i just let em run for a while in the morning.

 

[J E Custom]

As a machine shop owner and Journeyman tool and die maker, I own numerous lathes, both manual and CNC and for practical purposes, no lathe with the exception of a second operation toolroom lathe, is capable of holding 1 ten thousandths of an inch.

It's impossible simply because the TIR of the spindle precludes that. The only way a spindle (the headstock end( can hold 0.0001 is if the bearings are Class 5 and 99% of machines sold for general use, aren't. Secondly, 1 tenth is entirely dependent on factors such as temperature of the workpiece and tool deflection.

Anyone who claims they are holding 1 tenth accuracy in a shop enviroment without very special considerations is simply FOS.

Besides, most laymen can't measure 1/10th accurately anyway, tailstock alignment or not, floating reamer or not. Not gonna happen.

I 100% agree that there are machine tolerances that we are stuck with, but to settle for .001
on the your part when you can do better is a problem in my opinion.

I only said I tried to get the readings down as low as possible. The machine tolerances are there but you can still try to minimize the Human error.

Garycrow said tolerances stack, and I also agree with that. So why not minimize the human tolerances and lower the overall tolerances to the machine limits.

My point is and will always be, Don't settle for less than your best if you expect the best from your work. The same is true for working up loads for accuracy, I never stop trying and if I can improve the accuracy/group by a few thousandths I have to try.

I am not claiming to get zero tolerance on anything I do (But I try)and I work to the limit of my equipment if possible.

Shoddy works seems to be very common in Gun smithing now days (Because everyone can do it)and from some of the problems I have seen and some I have heard on this site, Good enough may be ok for some but I know others like my self that don't settle for anything but there best.

How much quality will always be subject to debate because different people have different philosophies on what is good enough.

Sorry I try so hard. But I don't intend to change. It may take me longer to do a set up than others, but I am in no hurry and have no intent to compromise My standards. In fact, I try to do every task better than the last time.

I am retired and time is not a factor in doing the best work I can.


J E CUSTOM

 

[SidecarFlip]

I am as well (retired) though I do manage a couple employees (sort of). I trust my employees to be qualified enough to turn out work that is accurate and dimensionally correct to a customers specification.

You don't hire someone off the street with no experience and expect them to hold a tolerance specification. Don't work that way. Experience and skill comes with a price, like everything else in the trades.

When I see a stick with ground threads on the barrel blank and internal ground threads in the receiver (barring the tolerance the barrel maker held the rifling to), I might buy 0.0001. Until then, no way.

To accurately measure a tenth repeatedly, requires coordinate measuring equipment and / or comparative measurement, neither are available to an average smith because it's cost prohibitive and certainly not attainable in an average shop.

Furthermore, I can make just about any stick shoot sub moa on the bench through careful loading practices... In real life, I'm not that good....lol Glad most animals have a kill zone larger than a paper target at 200 yards.....