Bore straightness, important?

[Alex Wheeler]

Why would you not talk gunsmithing on the gunsmithing forum? I thought that's what this place is for. That's why I am here to learn and discuss gunsmithing techniques.

Like Dave says, dont do anything to make the phone ring. Same applies here. If I posted my opinions on the best way to chamber a barrel Id be on here for a month solid defending those opinions. My favorite thing about Benchrest is that every target, match win, record, ect. is on the record. Its the ultimate proof.

 

[jackieschmidt]

Ever person that makes a post on any Forum on the Internet where the discussion centers around the runout in a Barrel’s ID should first look through a barrel as it is spinning in the lathe before you ever make a comment.

 

[DaveTooley]

Either throat or muzzle has to be crooked right? And if I remember correctly you prefer to have your throat true.

So a bullet has say .375" bearing surface. How much of an affect does the absolutely most crooked barrel ever made have on the angular difference between the bore and the crown in the last .375" inches of the barrel?

 

[john 800]

Why would you not talk gunsmithing on the gunsmithing forum? I thought that's what this place is for. That's why I am here to learn and discuss gunsmithing techniques.

As much as it sucks, I understand Alex’s hesitation to post about specifics with chambering and such. Including but not nearly limited too: It could (WILL) turn into an argument about how to do things, sometimes guys that know what know what they are talking about dissagree, sometimes a 15 year old google expert will argue about how to do things. Also bear in mind Alex is on here representing his business. Its really too bad, it could be a very interesting and informative conversation

 

[darkangel_r2]

So a bullet has say .375" bearing surface. How much of an affect does the absolutely most crooked barrel ever made have on the angular difference between the bore and the crown in the last .375" inches of the barrel?

From observing barrel indexing tests it can be several minutes of angle. But i suppose that number includes the harmonic amplitude itself so its hard to answer that exactly right now. But proper indexing can eliminate most of the negative effects of a curved bore in terms of harmonics and how the barrel moves.

What I don't think has been studied is the effect a curved bore has on the crown. If the bore is curved at the muzzle one side of the bullets bearing surface is going to lose contact with the bore before the other allowing gas to escape on one side first.

 

[jackieschmidt]

You will find that when the discussion of chambering barrels comes up. 95% of the conversation centers around what the heck you true up to what.

 

[Alex Wheeler]

As much as it sucks, I understand Alex’s hesitation to post about specifics with chambering and such. Including but not nearly limited too: It could (WILL) turn into an argument about how to do things, sometimes guys that know what know what they are talking about dissagree, sometimes a 15 year old google expert will argue about how to do things. Also bear in mind Alex is on here representing his business. Its really too bad, it could be a very interesting and informative conversation

Normally that would be true. But do you remember me promoting my business? In fact I avoid that. I put out a lot of info, not everything but a lot.

 

[john 800]

Normally that would be true. But do you remember me promoting my business? In fact I avoid that. I put out a lot of info, not everything but a lot.

I have enjoyed alot of your posts over the years. They have always been simply discussing shooting, reloading or gun builds or whatever question someone asked. That is not really where I was going with my comment, I was just pointing out that getting in a pissing match on the internet could possibly affect your business in a negative way and I don’t blame you for not wanting to post some things.

 

[WSnyder]

Well...The more curvature the bore has the more effectively crooked the crown would be correct?

Either throat or muzzle has to be crooked right? And if I remember correctly you prefer to have your throat true.

What if you were to dial in the chamber at the throat and two inches further into the bore and then cut the chamber. Would the chamber/throat be effectively crooked? What if you were to then flip that barrel end for and dial in at the crown and two inches further into the bore and cut it. Would the crown effectively be crooked?

 

[Edd]

I’m going to say it like this there’s a bunch a great gunsmiths on this website that does a great job but 99% of them wouldn’t know a straight hole if they seen it I’m sorry.

What method would someone use to recognize a straight hole?

 

[Stan Taylor]

What method would someone use to recognize a straight hole?

The easiest way to explain it is a trained eye knowing how to read the hole in barrel that your looking threw I probably look at 50 too 60 barrels a day grading for straightness
Here’s a straight hole.

 

[jackieschmidt]

What method would someone use to recognize a straight hole?

There on lies the problem.

it is easy to see the crooked areas in a barrel. All you have to do is look.

Ascertaining whether an ID of a long object is truly straight takes equipment that is quite specialized.

Every time someone says”curved” in one of these discussions, they just proved that they do not understand the problem, The term “curved” denotes a continuous parabolic shape, much like a banana. This is not what is exhibited in a barrels ID.

Since I have the means to do it, I have taken the time to actually cut a barrel into multiple 2 inch sections to show shooters exactly what is going on. It clearly showed how the ID can wander by several thousandths one way or another in what can best be described as a random pattern.

I made a detailed post explaining the entire phenomena. I posted pictures. I laid it out in a practical manner, easy to understand, and easy to see.

Very few seemed to care. They would rather listen to conjecture over on “bang-a-way.com” from someone trying to sell them something.
Most have no idea of the problems encountered in deep hole drilling of small diameter holes in long sections.
If barrel ID’s were indeed truly straight, all of this would be a moot point. But since they are what they are, Gunsmiths and Craftsmen have to get creative in figuring out what to true up to what.

As a Machinist, you look at a job like this strictly from that viewpoint of a machinist.. As most know, if you are dealing with something that is not straight, you can true any two points in it’s length to run truly straight with each other. The problems arise when you then attempt to plug in a 3d point.

So, logic dictates that you pick out two important points, true them up, and then machine that third point to run truly straight with the first two predetermined spots. You then have three points truly straight with each other.
Everything else in between, you don’t worry about.

The three points I want running true are the chamber, the throat,(described as the very first thing the bullet encounters when it leaves the case), and the muzzle.

I can do this. In fact, that is how I chamber my barrels. It takes a little bit of thought, but it is the best method I have come up with when dealing with the anomalies you encounter in the ID of a barrel.

keep in mind, I am not a Gunsmith. To me, chambering and fitting a barrel is nothing but another machining procedure with predetermined requirements and tolerances that I have to meet.

And, I check my work. In a machine shop, you do not assume things. You check it to insure that your setup is indeed viable and produced the results required.

 

[Edd]

When you set up the barrel to run straight at the throat and muzzle, how much runout, on a typical barrel, will there be a half inch from those two points?

 

[jackieschmidt]

When you set up the barrel to run true at the throat and muzzle, how much runout, on a typical barrel, will there be a half inch from those two points?

It varies from barrel to barrel, but I have seen as much as .001 TIR from one point just an inch from another. In other barrels, not enough to even pick up with a “tenth” indicator.
In my opinion, the worst scenario is having one of those spots at the chamber end. You then have to decide exactly where the throat will be established and true that point so when you single point the chamber true to that point, things won’t get skewed when the reamer pilot is in that area.

As you can see, sometimes you have to compromise and shoot for the best results within the pera meters you were handed. Often, when I chuck one of my barrels up, I have to think about it for a while to figure the best plan of attack.

 

[Dusty Stevens]

The easiest way to explain it is a trained eye knowing how to read the hole in barrel that your looking threw I probably look at 50 too 60 barrels a day grading for straightness
Here’s a straight hole.

Concentric rings

 

[Stan Taylor]

Concentric rings

I couldn’t have said it any better myself thanks pal.

 

[WSnyder]

As you can see, sometimes you have to compromise and shoot for the best results within the pera meters you were handed. Often, when I chuck one of my barrels up, I have to think about it for a while to figure the best plan of attack.

^^^This is what I'd think a lot of us do. You chuck the barrel up and start taking a look at what you've got and then with some experience you decide how you're going to deal with that particular barrel. I can tell you barrel manufacturer preference comes into play here for me. It's not to say that one manufacturer will shoot better than another but lets just say a particular manufacturers barrel may be more consistent straightness wise which to me means faster setup in the lathe and less decisions that have to be made finishing that barrel. I'm prone to analysis paralysis so if I can simplify the decision making I'm better off

 

[PWS]

I’m just a home-shop hack but it seems to me that most people get hung up angles when the bore isn’t “straight” but the guys that are making a living turning out top notch work focus on concentricity.

 

[msalm]

In my barrel bin I still have a 6mm blank from an old match bbl maker. 10tw magnum sporter bbl. Most crooked bore I’ve seen and I can see bore straightness by reading the rings. Some of the older Rock Creek barrels had some good curves on them and the biggest problem is just setting them up to machine. I chamber much as Jackie does and getting that throat centered is the trick with longer cartridges. On some you can make the mistake of dialing in on the throat while using a snug pilot on your reamer that is 1/2” ahead of that point…your throat won’t be perfectly concentric…. Still need to chamber that 6mm someday, but every time I look through it I get a mild reaction just contemplating the attempt. When I get a good chamber in it and time it (first step obviously), I have no doubt it’ll shoot fine.

 

[Sniperhandle]

If your barrel is not straight, Not to worry, You can fix this by getting some cream from "bentcarrot.com" along with simple straightening and stretching exercises.