I'm not talking about any barrel. I'm talking about technique in gunsmithing.
Question: Determining the curvature of the bore.
- Thread starter jfseaman
- Start date
I'm not talking about any barrel. I'm talking about technique in gunsmithing.
butchlambert
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Same answer. My technique may be different than yours. Who's technique is better? The technique that makes you warm and fuzzy!
Um, sure Butch. You know best.
butchlambert
Site $$ Sponsor
Didn't mean to upset you. You were asking questions and you got answers.
Simply put, if you have a way to eyeball the bore while it is on rollers, you can determine if it has a bad helix. Different chambering methods have won matches, do what makes you feel bestus.
Now I have seen some terribly drilled and rifled barrels shoot very well.
Simply put, if you have a way to eyeball the bore while it is on rollers, you can determine if it has a bad helix. Different chambering methods have won matches, do what makes you feel bestus.
Now I have seen some terribly drilled and rifled barrels shoot very well.
Darling Butch,
You didn't upset me. I'm not a little snowflake.
Yes, I asked a question and I got answers. Very productive for me. You were very nice to try to provide something useful.
Do you build rifles?
Do you win anything with them?
If so do they win often?
I respectfully ask this because I dont know you and it would give me some context in which to take your comments and then reply
Yes I build rifles, only for me. Trying to get into gunsmithing school as a third career.
No, I don't compete were you win anything except satisfaction. I do shoot 1000 and beyond as far as a bullet can go and I hit the intended target. At the moment I am working on building out this facility: https://www.facebook.com/groups/149824382271353/?ref=br_rs
I have lots of help building out the facility. Both what and where to place targets. More "experienced" shooters. They are at a PRS competition this weekend.
Expert, no.
Physics is physics. Which where the question originates. I recently acquired a DTA SRS. One of the barrel makers states "our Desert Tactical Arms barrel extensions are installed and timed to the curvature of the bore. This ensures that the barrels are indexed perfectly straight with all curvature of the barrel pointing to the 12 o’clock position".
No, I don't compete were you win anything except satisfaction. I do shoot 1000 and beyond as far as a bullet can go and I hit the intended target. At the moment I am working on building out this facility: https://www.facebook.com/groups/149824382271353/?ref=br_rs
I have lots of help building out the facility. Both what and where to place targets. More "experienced" shooters. They are at a PRS competition this weekend.
Expert, no.
Physics is physics. Which where the question originates. I recently acquired a DTA SRS. One of the barrel makers states "our Desert Tactical Arms barrel extensions are installed and timed to the curvature of the bore. This ensures that the barrels are indexed perfectly straight with all curvature of the barrel pointing to the 12 o’clock position".
Dusty Stevens
Shiner
i guess desert tactical arms do AR barrels?
Um, no. DTA does not do AR barrels. I don't do ARs. Well, one just because, in 6mm-6.5 Grendel aka 243 LBC aka 6mmAR aka 6mmARP. Gas piston instead of direct impingement.
Dusty Stevens
Shiner
i just noticed in your post that they timed their barrel extensions. carry on. ive never heard of them so what do i know?
Thanks for your reply.
I asked earlier why you wanted to know the answer to your question and what relation the answer would have to building an accurate rifle. Your reply was that if the bore was curved (which invariably they all do to a greater or lesser degree) it would shoot left or right unless the curve was up or down.
I guess the choices we have when chambering is between centers which personally I find a bit too vague or working within the headstock which I will focus on.
My choice is then which two parts of the barrel will I indicate? I prefer throat and muzzle and then I disregard the rollercoaster ride the bullet takes between these two points. I bore the chamber out up to the indicated throat and then ream to finish chamber size. I have absolutely no idea what amount of curvature I have between the throat and muzzle nor does it interest me one bit. So long as my tenon shoulder is cut square at 90 degrees to my chamber and throat the rifle will shoot straight in both the horizontal and vertical plane (allowing for drop) regardless of any internal curvature.
If you set up the barrel like Gordy Gritters and dial in the first "x" amount of the barrel that will be the chamber and throat then your muzzle will end up running out and it will then be timed to the vertical plane with extra work being needed for in my opinion no extra gain over the earlier method I described that I use.
This brings us back to your original point and how relative it is to know whats happening in the bore along its length?
Personally I think the curvature found in good quality rifle barrels is not enough to concern yourself about. If the bullet is offered to the throat in both an axially and radially concentric way and the point of exit from the muzzle is also concentric then you will have an accurate rifle, depending on components used and the load development it could be record braking accurate. Lots of match and championship rifles are built using the method I describe and like me I dont think any of those rifle builders will think much about the bullets journey from throat to muzzle taking into account the tolerances match quality barrels are made to.
Just my 2 cents
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@Alex Wheeler shows exactly what I mean.
Restating with different wording so you can correct me if I have it wrong.
As I understand it, @Curious said, make sure the chamber/throat/breach face are all coaxial to the bore at the breach. The muzzle doesn't matter at that stage.
However, if you indicate the curvature of the muzzle exit, what is in between does not matter. Knowing the "crown" of the bore will let us make the breach coaxial to the action/chamber/throat. If we mark the point at which the muzzle is at it's highest deviation from the breach axis and tune the barrel/action interface so that this deviation is centered up then there will be less left right correction.
I'm going to add one thing to the above paragraph. An observation. Where I know the direction the muzzle "crown" as in "crown" like a piece of lumber like @Alex Wheeler s picture. Almost always, that is the direction the point of impact is going to move with barrel heating. Example: My new DTA, I know the muzzle points "up" from being completely axial with the bore at the breach. When I get to round 6 of say a 10 round string, the point of impact starts to move up. The hotter the barrel gets the more the point of impact moves. This is not the only rifle I have where I have POI shift with barrel heating.
So this brings me to @butchlambert s comment
If the "crown" curves up and the POI moves up with barrel heating, this can be easily mapped. If it is at a random angle mapping this POI shift and factoring in wind effects make for a much more difficult shooting solution.
So what I plan on doing is adding an additional step to setting up a barrel in my lathe. Indicate the breach axially true to the axis of the head stock. Determine the point of deviation at the muzzle by measuring the high and low spots with another indicator rod. Touch up the tenon so the action locks up under torque with high end of the barrel curvature pointing up relative with the action center line. After that, when crowning and turning for muzzle devices such as brakes. True the muzzle to the axis of the head stock to make sure the muzzle crown shape and threading for barrel devices is axial to the bore of the muzzle end.
Hopefully, like my DTA, when the barrel heats up during fast or long firing strings, I will know how much the barrel will rise.
Objective data: My DTA 300WM barrel had a loose barrel extension. Just hand tight. Not an issue for safety. However, during shooting strings the POI would move "unpredictable". Last Wednesday I torqued the barrel down to the extension. Today POI shift during long strings was straight vertical.
Restating with different wording so you can correct me if I have it wrong.
As I understand it, @Curious said, make sure the chamber/throat/breach face are all coaxial to the bore at the breach. The muzzle doesn't matter at that stage.
However, if you indicate the curvature of the muzzle exit, what is in between does not matter. Knowing the "crown" of the bore will let us make the breach coaxial to the action/chamber/throat. If we mark the point at which the muzzle is at it's highest deviation from the breach axis and tune the barrel/action interface so that this deviation is centered up then there will be less left right correction.
I'm going to add one thing to the above paragraph. An observation. Where I know the direction the muzzle "crown" as in "crown" like a piece of lumber like @Alex Wheeler s picture. Almost always, that is the direction the point of impact is going to move with barrel heating. Example: My new DTA, I know the muzzle points "up" from being completely axial with the bore at the breach. When I get to round 6 of say a 10 round string, the point of impact starts to move up. The hotter the barrel gets the more the point of impact moves. This is not the only rifle I have where I have POI shift with barrel heating.
So this brings me to @butchlambert s comment
If the "crown" curves up and the POI moves up with barrel heating, this can be easily mapped. If it is at a random angle mapping this POI shift and factoring in wind effects make for a much more difficult shooting solution.
So what I plan on doing is adding an additional step to setting up a barrel in my lathe. Indicate the breach axially true to the axis of the head stock. Determine the point of deviation at the muzzle by measuring the high and low spots with another indicator rod. Touch up the tenon so the action locks up under torque with high end of the barrel curvature pointing up relative with the action center line. After that, when crowning and turning for muzzle devices such as brakes. True the muzzle to the axis of the head stock to make sure the muzzle crown shape and threading for barrel devices is axial to the bore of the muzzle end.
Hopefully, like my DTA, when the barrel heats up during fast or long firing strings, I will know how much the barrel will rise.
Objective data: My DTA 300WM barrel had a loose barrel extension. Just hand tight. Not an issue for safety. However, during shooting strings the POI would move "unpredictable". Last Wednesday I torqued the barrel down to the extension. Today POI shift during long strings was straight vertical.
You seem to have taken something quite different from what I wrote. By adding your own words you are now describing something different to me. I appreciate internet fora isn't the best medium for communication on such technical matters at times but I think others get my drift.
With respect I feel you are looking for the solution to a problem that I haven't found to exist. My rifles built using the method I described, indicating throat and muzzle yet dont seem to demonstrate the problems you seem to be concerned with. My interest is LR benchrest so the barrels do heat up over 5 & 10 shot strings yet somehow seem to hold together my group sizes
There could be POI rise as a result of changes in velocity from heating the cartridge and barrel. I try not to chamber until I am ready to shoot.
I stop shooting if I can't hold the barrel comfortably with my hand fully wrapped around it. Additionally I use temperature stickers.
@Alex Wheeler I have a great deal of respect for your experience and contributions. Heat based barrel walking is somewhere we may stay in disagreement. It's a physics issue. The barrel close to the stock will be hotter than the barrel above the stock line. This heat differential will cause the muzzle to rise or as I call it walk. My Bartlien, Hart, Benchmark and Pac-Nor barrels in "conventional" shaped stocks, be they wood, laminate or fiberglass/carbon fiber composite, all walk with heat. As you say there is probably also a heat based velocity change as well.
My barrels in vented free float tubes like the Ruger Precision Rifle or DTA SRS don't have that problem. The Ruger Precision uses a cold hammer forged barrel (AFAIK). It walks with heating, also a physics issue as the density of the crystalline structure is not consistent. The DTA SRS 300 Win Mag POI change is exactly as you describe. Velocity change as a result of heating.
I stop shooting if I can't hold the barrel comfortably with my hand fully wrapped around it. Additionally I use temperature stickers.
@Alex Wheeler I have a great deal of respect for your experience and contributions. Heat based barrel walking is somewhere we may stay in disagreement. It's a physics issue. The barrel close to the stock will be hotter than the barrel above the stock line. This heat differential will cause the muzzle to rise or as I call it walk. My Bartlien, Hart, Benchmark and Pac-Nor barrels in "conventional" shaped stocks, be they wood, laminate or fiberglass/carbon fiber composite, all walk with heat. As you say there is probably also a heat based velocity change as well.
My barrels in vented free float tubes like the Ruger Precision Rifle or DTA SRS don't have that problem. The Ruger Precision uses a cold hammer forged barrel (AFAIK). It walks with heating, also a physics issue as the density of the crystalline structure is not consistent. The DTA SRS 300 Win Mag POI change is exactly as you describe. Velocity change as a result of heating.
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butchlambert
Site $$ Sponsor
@Curious and @Alex Wheeler,
Respectfully guys, I'm not an idiot. I don't treat you that way, please try not to treat me that way.
@Curious, if my restatement does not match what you said it only shows that I did not understand what you said or you don't understand my restatement. Nothing more. I think it matches and matches @Alex Wheeler 's lower diagram. As for:
However
The DTA SRS is a switch barrel rifle. Physics is physics, barrels have a curve as in the breach and muzzle are not exactly coaxial.
I asked how to determine the deviation for a valid reason. When switching barrels on any switch barrel rifle, having this deviation in the same plane for every barrel minimizes scope adjustment required between barrels. Very simple, valid reasoning. If this deviation is all in the vertical plane then only elevation changes need to be made. A simple chart or label for each barrel, done. If you have to make changes in multiple planes because the barrels are not all indexed in one plane, adjustment is more complicated. In real life will it work perfectly, of course not. Like reloading for accuracy, it's about reducing compounded deviation.
If I were asking for a conventionally built rifle, as in threaded barrel tenon torqued into an action, I agree, it is a non issue, though as @Will Henry points out, it is worth checking just in case. @Stan Taylor takes it very seriously as a mater of pride in the product of his company and his own work. Super great. Makes me want to try a barrel from them. For a switch barrel, it is perhaps a minor issue but of course, any issue to add to the list of things to check at a competition adds to the list of possible failure points. Mantra: reduce cumulative deviation in every aspect, ammunition, rifle and scope.
What prompted the question of the original post was explained in reply #28 that @Curious asked for http://forum.accurateshooter.com/th...ture-of-the-bore.3936477/page-2#post-37083885 I was reviewing buying DTA SRS prefit barrels vs. fitting them myself and came across that comment.
@Will Henry and @Stan Taylor did a great job of explaining why I should at least check if I am going to fit a DTA SRS barrel myself. @Alex Wheeler s lower diagram was great in demonstrating exactly what I was referring to. @Curious s
My question was answered long ago in this thread. It is part of the reason I purchased a long probe indicator.
Too many replies after the question was answered contained "should" and "shouldn't" either explicitly or implied. IMO a very aggressive communications form.
Good shootin' to y'all.
Respectfully guys, I'm not an idiot. I don't treat you that way, please try not to treat me that way.
@Curious, if my restatement does not match what you said it only shows that I did not understand what you said or you don't understand my restatement. Nothing more. I think it matches and matches @Alex Wheeler 's lower diagram. As for:
I think "concerned" is too strong a word. I only asked how it was determined. You asked why, then seem to take that as "concerned". I was looking for a learning opportunity. You say it doesn't matter with "quality barrels". Alex says it doesn't matter with "quality barrels". Butch says it doesn't matter with "quality barrels". Perhaps it doesn't matter with "quality barrels".
However
The DTA SRS is a switch barrel rifle. Physics is physics, barrels have a curve as in the breach and muzzle are not exactly coaxial.
I asked how to determine the deviation for a valid reason. When switching barrels on any switch barrel rifle, having this deviation in the same plane for every barrel minimizes scope adjustment required between barrels. Very simple, valid reasoning. If this deviation is all in the vertical plane then only elevation changes need to be made. A simple chart or label for each barrel, done. If you have to make changes in multiple planes because the barrels are not all indexed in one plane, adjustment is more complicated. In real life will it work perfectly, of course not. Like reloading for accuracy, it's about reducing compounded deviation.
If I were asking for a conventionally built rifle, as in threaded barrel tenon torqued into an action, I agree, it is a non issue, though as @Will Henry points out, it is worth checking just in case. @Stan Taylor takes it very seriously as a mater of pride in the product of his company and his own work. Super great. Makes me want to try a barrel from them. For a switch barrel, it is perhaps a minor issue but of course, any issue to add to the list of things to check at a competition adds to the list of possible failure points. Mantra: reduce cumulative deviation in every aspect, ammunition, rifle and scope.
What prompted the question of the original post was explained in reply #28 that @Curious asked for http://forum.accurateshooter.com/th...ture-of-the-bore.3936477/page-2#post-37083885 I was reviewing buying DTA SRS prefit barrels vs. fitting them myself and came across that comment.
@Will Henry and @Stan Taylor did a great job of explaining why I should at least check if I am going to fit a DTA SRS barrel myself. @Alex Wheeler s lower diagram was great in demonstrating exactly what I was referring to. @Curious s
hit the nail on the head for @Alex Wheeler s upper diagram. Which is how I've done it in the past. @Alex Wheeles s reply # 25 http://forum.accurateshooter.com/th...ture-of-the-bore.3936477/page-2#post-37083735 demonstrates again his lower diagram.
My question was answered long ago in this thread. It is part of the reason I purchased a long probe indicator.
Too many replies after the question was answered contained "should" and "shouldn't" either explicitly or implied. IMO a very aggressive communications form.
Good shootin' to y'all.
Alex Wheeler
Site $$ Sponsor
I am not sure how I was treating you like an idiot? I understand basic physics as well and I think you're thinking is flawed. When you ask questions you're going to get more than one side. And when someone posts a question like how do I find the curve of a hole I have to assume a certain level of experience. So I'm out someone else may be able to help you.
Ha ha ha. Your funny darling. Have you ever done improvised comedy?
@Alex Wheeler you did a great job of answering the question. Thank you. It was truly helpful.
Some of the words in the replies could be interpreted as condescending. Example "question like how do I find the curve of a hole" is one of those. Adding the "I have to assume a certain level of experience" part where you did could be interpreted as condescending. It's hard to tell in the impersonal communications form of internet posts. If it was not intended, no problem.
BTW
is not what I asked. This could be part if the misunderstanding. Though your diagram demonstrates exactly what I was referring to in the original post. Thank you for that.
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