Rubicon Prec.
New member
In a blind taste test, would any shooter be able to say without a doubt which method the barrel was dialed in the lathe by looking at his target?
JerrySharrett
Senile Member
First off, we are benchrest here. Generally a PPC and a 21" or there abouts barrel. We don't do 499 Mashemflat Magnums with super long, whippy, barrels.
The in-bore runout on the worst barrel I have ever spin on a lathe had about 0.013" total curve. It was a 20.5" barrel with a curve that looked like a 2-girl jump rope. On this barrel the OD ran true but the ID was curved. When I finished with that barrel I cut it in two parts cutting at the most curve. The total distance, measuring wall thickness variation was 0.013".
(what does a 40 degree shoulder in the chamber have to do with bore runout? For three years I shot a modified 6PPC with a 40 degree shoulder in 100/200 and 600 yard competition. The 6-40Dune. Never thought a 40 degree shoulder effected runout???)
.
.
coyotechet
Chet
I use the Gordy method with the Grizzly rod and indicators, indicating the 2 spots throat and the chamber end let the muzzle be what ever during the full chambering and threading of the barrel. Then I turn the barrel around and indicate the muzzle end the same way using the Gordy method with the grizzly rod and indicators for two plus inches of the bore then cut the crown of the muzzle totally square to the barrels bore.
Chet
Chet
geo.ulrich
Member
Chet, you got it right only you don't need the rods just indicate 2 points , don't need stacked error with the rod.. we don't care where the muzzle is as long as in throat and in front is straight , same when you turn it 2 points at muzzle at least bearing length long....
Yes, you can
One method mentioned will require a big target (sometimes) to "get it on paper"
Does one method shoot any better than the other? At least in the ppc I can't see the difference and I have tried all of the above methods.
I have alot of bbl's for each rifle and it's nice to be able to switch around and not have to go hunting for the first shot.
Well anyway, lots of ways to skin the cat so the each his own. Personally, I think it's more about how good the bbl is in the first place!!
Richard
One method mentioned will require a big target (sometimes) to "get it on paper"
Does one method shoot any better than the other? At least in the ppc I can't see the difference and I have tried all of the above methods.
I have alot of bbl's for each rifle and it's nice to be able to switch around and not have to go hunting for the first shot.
Well anyway, lots of ways to skin the cat so the each his own. Personally, I think it's more about how good the bbl is in the first place!!
Richard
coyotechet
Chet
Maybe not but the aggs. sure are getting smaller for most and I will still put my wages of the indicated two point system.
Grizzly rod or not 2 points chamber end and muzzle end both square to the bore sure makes me fill good when I finish the job.
Chet
coyotechet
Chet
Richard you are so right in all of the above. But GOOD barrel work keeps it that way.
P.S. Richard are you coming to Mill Creek this weekend (Hope So).
Chet
Last edited:
F
Fussy1
Guest
You guys are making my head spin. I think that I need to watch some of the videos. 
I'd been thinking that the throat, and chamber end locations are pretty much the same. And if they are not, what can be done about it?
F1
I'd been thinking that the throat, and chamber end locations are pretty much the same. And if they are not, what can be done about it?
F1
Think of 3 points,
to indicate a barrel A: the back of the chamber B: the throat area and C: the crown. As stated earlier you can only use two of the points at a time. Either A and B, A and C or B and C.
The bores of barrels are not usually perfectly straight so depending on which method you use you indicate two of the three points.
Lets say you choose to do A and B. You would indicate ahead of the throat by at least the caliber of the bullet, once you get that to zero you would do the back of the bbl to zero. If these two points are both zero the crown end is going to have runout but the chamber and throat area is perfectly inline with the bore axis. You would then drill and bore the chamber before running the reamer in.
If you do the B and C method you would indicate the throat to zero and the crown to zero and the back of the chamber would have the runout. Drill and bore and ream.
A and C would be on steady rest, indicate the back true and the crown true and the throat will have the runout.
It's a little more involved than that but you get the idea. There are pros and cons to all of them.
All methods will work, but sometimes one better than the other depending on how straight the bbl is.
Richard
to indicate a barrel A: the back of the chamber B: the throat area and C: the crown. As stated earlier you can only use two of the points at a time. Either A and B, A and C or B and C.
The bores of barrels are not usually perfectly straight so depending on which method you use you indicate two of the three points.
Lets say you choose to do A and B. You would indicate ahead of the throat by at least the caliber of the bullet, once you get that to zero you would do the back of the bbl to zero. If these two points are both zero the crown end is going to have runout but the chamber and throat area is perfectly inline with the bore axis. You would then drill and bore the chamber before running the reamer in.
If you do the B and C method you would indicate the throat to zero and the crown to zero and the back of the chamber would have the runout. Drill and bore and ream.
A and C would be on steady rest, indicate the back true and the crown true and the throat will have the runout.
It's a little more involved than that but you get the idea. There are pros and cons to all of them.
All methods will work, but sometimes one better than the other depending on how straight the bbl is.
Richard
You guys are making my head spin. I think that I need to watch some of the videos.
I'd been thinking that the throat, and chamber end locations are pretty much the same. And if they are not, what can be done about it?
F1
Barrels are not bored straight. CUSTOM BLANKS are not bored straight and subsequent turning/contouring/fluting operations turn them into snakes....
The thinner and longer they are the crookeder they may be.
I've had BR quality, custom-actioned, professionally built name-brand hunting barrel blanks crooked enough that, when chambered between centers (NOT BY ME, but by well-known professionals) with the muzzle "directly in front of the throat" they printed 18" off at 100yds......enough that one could not get the scope adjusted to poi properly, rings needed to be lapped over.
Furthermore all this talk of using "the ends" of the blank for any sort of indication scares me. (Incidentally, I went to gunsmithing school full-time for two years and learned to center up barrels using these ends) But I've since learned about, and measured the "lapping bell" which occurs on each end of a blank. The inner bore of a custom barrel blank is wallered out, enlarged and eccentric such as to be unusable for any sort of true centering on each end, that area where the lap is reversed....
So, one must start by reaching in (or cutting off) an inch or more from each end, THEN depending on ones abilities one must "pick two points" from there.....I choose to start the centerline of the entire rifle build around a 3" long section of the bore centered on the ogive of the bullet. I then adjust the bedding as desired to make the rifle recoil as I see fit.
If one of my builds were fired in deep space I'd want it to recoil directly rearward, spinning like a wagon wheel..... IMO this makes for an "automatic" or easy_shooting rifle. One which isn't sensitive to how it's held.
This is actually perty hard to accomplish.
2 things.....
#1, I've been frightfully successful at achieving this goal and
#2, It's astonishingly repeatable.
I've got lots of barrels and blanks kicking around. I'll sometimes assess a blank and set it aside. Later I can easily take one of these blanks, COVER UP MY INDEX MARKS and re-set the blank into the lathe randomly with no attempt to match or duplicate my prior setup. peel the tape to find my old setup to match my new.
As a machinist, this makes me grin and shake my head
every time
F
Fussy1
Guest
Thank you for the detailed explanations, guys! I think that I would have to choose A/B, Richard. Alinwa, the things that you benchresters describe go far beyond hunting rifle procedures. I associated with shooters years ago, that would buy a rifle, and head for the range. Accurate rifles (usually factory) would be kept, the also-fans were traded/sold off. This strategy was probably cheaper than custom work, but we are talking about hunting accuracy, not bench work. I have great regard for the work of the gunsmiths on this forum.
F1
F1
Last edited by a moderator:
B
Bill in AZ
Guest
Interapid Indicator, which configuration, which resolution?
I have an old and abused Brown 7 Sharpe horizontal indicator that has been abused for decades before it was given to me, so I am looking to replace it.
At MSC they have several Interapid indicators, both Horizontal mount and vertical mount, I have only used horizontal style, any reason to look at the vertical mount indicators?
ALSO these indicator are offered with 0.0005 graduations (half a thou) or 0.0001 graduations (tenth thou). Does the tenth on become too fussy to set up or is the finer resolution a good thing?
And then I need to select an extension point or two to reach into the bore.
I have an old and abused Brown 7 Sharpe horizontal indicator that has been abused for decades before it was given to me, so I am looking to replace it.
At MSC they have several Interapid indicators, both Horizontal mount and vertical mount, I have only used horizontal style, any reason to look at the vertical mount indicators?
ALSO these indicator are offered with 0.0005 graduations (half a thou) or 0.0001 graduations (tenth thou). Does the tenth on become too fussy to set up or is the finer resolution a good thing?
And then I need to select an extension point or two to reach into the bore.
GeneT
Active member
10ths works
Get the 0.0001" - you're going to lose precision with a long tip anyway. Also, while interapid is a better indicator (probably the best) Mitutoyo and Gem make some of their indicators with a long thin body that will insert into the body portion of a cut chamber...
GsT
Get the 0.0001" - you're going to lose precision with a long tip anyway. Also, while interapid is a better indicator (probably the best) Mitutoyo and Gem make some of their indicators with a long thin body that will insert into the body portion of a cut chamber...
GsT