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Gunsmithing Short Action Customs: Timing curvature of the bore

Mgordon

Mgordon

Gunny Sergeant
Commercial Supporter
Full Member
Minuteman
Nov 29, 2007
1,792
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40
Wellington, Ohio
www.shortactioncustoms.com
Shooters,

Here are two quick videos of myself timing the curvature of the bore on two different barrels.

The first barrel is a Schneider M40. The barrel has about .075" of runout on the muzzle end with the chamber end dialed in correctly. This barrel still shoots extremely well, however it has a slight curve to the bore.

The second barrel is a Bartlein M40 30 cal barrel. This one measures around .015" of muzzle runout. This barrel is extremely straight, most that we barrel up have a .020" - 050" muzzle runout.

Muzzle runout has nothing to do with accuracy, and we have had barrels with around .200" of muzzle runout that still shot extremely well. We like straight barrels however.


Locating the curvature of the bore

Locating the curavture of the bore on a Barlein M40

Thank you for watching.

Mark
 
Re: Short Action Customs: Timing curvature of the bore

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Frank Green</div><div class="ubbcode-body">Nice video's Mark!!!!

Later, Frank
Bartlein Barrels </div></div>

Says the guy who made the really straight barrel!
 
Re: Short Action Customs: Timing curvature of the bore

As a beginning amateur machinist, I really appreciate all the videos and time you guys spend sharing with the rest of us, and surprisingly, I've learned and enhanced my approach more from what I've seen here than from actual experience on a mill/lathe. Keep it coming!
 
Re: Short Action Customs: Timing curvature of the bore

and untill you spend a pile of money on a rig that your are forced to hold off your target because your scope doesn't have enough windage and you invest hrs trying to figure out how the hell to fix the scope base holes that must be off center all due to a barrel that shoots around corners!!! GGRRRRRR
 
Re: Short Action Customs: Timing curvature of the bore

This was actually pretty cool to see how you do that, great attention to detail.
Mark, have you ever received a barrel that had so much runout you just couldn't use it?
 
Re: Short Action Customs: Timing curvature of the bore

I had a barrel one time that was fluted from the manufacture that had around .200" runout on the muzzle. Something like that would definitely need to be timed.

Lets say you go to drop that barrel in the stock with out timing it and it is pointing into the 9 o'clock position. How is that going to affect your bedding? Will your action be straight? Lets say you bed it in like that then install a barrel that is very straight with out bedding. It would most likely touch the barrel channel of the action.

We time the curvature of the bore to ensure our barrels are not inducing any windage issues during firing, and to ensure the bedding is straight forward.

Mark
 
Re: Short Action Customs: Timing curvature of the bore

Mark , have you ever gotten a barrel that the OD was strait and the bore was crooked?

I fit up one about 12 years ago that the barrel was strait as can be on the outside but the bore had some .060" runout.
 
Re: Short Action Customs: Timing curvature of the bore

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 2156SMK</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Frank Green</div><div class="ubbcode-body">Nice video's Mark!!!!

Later, Frank
Bartlein Barrels </div></div>

Says the guy who made the really straight barrel! </div></div>

Team effort bud! Not just one guy!!!!

We do what we can to make the straightest tubes!

I feel it's also another
+1 for cut barrels.

After a button barrel is rifled as a blank they have to re stress relieve the blank. Then it gets contoured and any secondary work like fluting etc...in these after stress relieving machining operations any residual stress in the blank the machining operation can relieve any left over stress. This can effect the barrel in several ways.

Also how the barrel is set up for contouring etc...can have an effect on how true the barrel will run. Some makers take short cuts in the turning/machining operation steps.

With all that being said all barrel makers fight drilling as straight a hole as possible. Your drilling a blind hole in the barrel blank. How nice the drill, drills, how nice the material is your drilling/machining in etc...are all variables as well.

Later, Frank
Bartlein Barrels
 
Re: Short Action Customs: Timing curvature of the bore

Again,the point of these videos was not to brag up or bring down any barrel maker, its just to show why we feel timing the curvature of the bore is important and that barrels all have a slight or moderate curvature to them.


Mark
 
Re: Short Action Customs: Timing curvature of the bore

I don't believe anyone would view them as an endorsement or critique of any particular maker Mark, I sure didn't see it that way.

Thanks again for the education, and keep those vids coming!
 
Re: Short Action Customs: Timing curvature of the bore

I didn't view it that way Mark, i thought the video was fascinating to see, i finally understood what you were talking about in my build sheet honestly and appreciated both the new videos.
 
Re: Short Action Customs: Timing curvature of the bore

Are Schneider barrels normally that bad?
 
Re: Short Action Customs: Timing curvature of the bore

Let me ask a theoretical question. You have a 24" bbl with .020" runout. You have it "timed" so the runout is 90 degrees. If you site rifle dead on at 100yds will the runout put and additional 3" of right windage on the target at each additional 100 yd increments? This sounds off to me but if the bullet is leaving the bbl "off verticle" it will never fly true?
 
Re: Short Action Customs: Timing curvature of the bore

Neat...so many details that go into building accurate equipment.
 
Re: Short Action Customs: Timing curvature of the bore

I will be honest. I had no idea the dang things were crooked.
In fairness, I'm not 100% sure what I'm looking at, it just looks like the darn thing is slightly warped.

So....I'm assuming that the "curve" is to be threaded such that it curves in a vertical plane versus a horizontal one when installed on the receiver, right?

Sorry if this question is stupid.....I just had no idea barrels were shaped like a banana (for lack of a better term).
 
Re: Short Action Customs: Timing curvature of the bore

Jethro3898,

Some barrels are straighter than others. The Bartlein in my video represents a barrel on the straight side. The Schneider is a barrel kind of in the middle of the pack, and I have seen barrels twice as bad as the Schneider barrel.

There is no way to drill a perfectly straight hole in 30" of steel.

What we do is find the curvature of the bore on each barrel we install. We then time the receiver threads so that as the action gets torqued on, the barrel curving up into the 12 o'clock position. This way the bore is pointing straight forward and up, there should be no windage issues and your barrel sits properly in the barrel channel.

Let me ask you this question. Lets say you have a builder makes you a 308 Win. When they do the work, the barrel is timed into the 9 o'clock position with a measured runout of .075" at the muzzle. Lets just assume that at half the barrel length where the barrel is in the stock, you have .0375" of runout in the 9 o'clock position.

Now your builder is bedding the rifle in a McMillan Gel Coated A5. There is .025" of clearance on both sides of the barrel in the channel.

Now you decide that you want an identical .260 barrel made up. Lets say this barrel has the same runout, but this time its curving into the 3 o'clock position with around .0375" at the middle of the barrel.

You can run into problems now that your action is basically bedded in at an angle so that the curved barrel is centered into the barrel channel. Then you install a new barrel that is curving into the opposite direction your action was bedded.

This is an extreme scenario, but it has happened and I have seen it while making another barrel from a previously barreled/bedded rifle.

We believe that timing the curvature of the bore is the best thing to do. Its just how we build rifles. I have no data that proves that your point of impact will shift or it does anything for elevation/windage. But as a builder, it makes sense.

Mark
 
Re: Short Action Customs: Timing curvature of the bore

This is a little on the subject as it pertains to curvature of the barrel.

I had this medium palma profile 6mm barrel with a 5" straight shank that I chambered in 243 as my comp rifle.
The reason for the 5" shank was to leave meat for a full 2" setback.
The barrel had about 0.030" muzzle runout and I set that to 12:00 just like Mark shows above.
I built this on a 700 action that I trued.
I also bedded the scope base on to the action.

I shot the barrel out and by that time, I had a couple surgeon actions on the bench to build my new comp rifles.

So I cut 2" off the back of the barrel and re-chambered the barrel into one of the surgeon actions.
I timed the muzzle runout the same way I always do.
Then I put the scope back on the new gun without chaning the original zero and went to zero the scope.
I was very pleased that my windage was spot-on and my elevation was only 1/10 mil high after setting the barrel back into the new receiver.

Think about ALL the things that have to come together pretty straight for that to happen.
 
Re: Short Action Customs: Timing curvature of the bore

That is really interesting to me.
I had no idea this was even a problem gunsmiths (at least good ones) even had to address. I could see that in extreme situations this could be a pretty big issue if not addressed.

Thank you for the reply Mark.
 
Re: Short Action Customs: Timing curvature of the bore

More videos please Mark!

Maybe you could expound on marking the top of the curvature and how you set it relative to the action when you set the headspace or barrel shoulder.

Nice work,
Justin
 
Re: Short Action Customs: Timing curvature of the bore

Once I saw a video of a barrel maker that straightened by hand all of their barrels after making them.
Is this not a common practice??
 
Re: Short Action Customs: Timing curvature of the bore

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Massoud</div><div class="ubbcode-body">Maybe you could expound on marking the top of the curvature and how you set it relative to the action when you set the headspace or barrel shoulder.</div></div>

I don't know how Mark does it, but what I do is make a sharpie mark on the top of the barrel.
Then I know where I want the receiver to time up a few degrees short of that mark to settle into the right spot once it's torqued on.
Timing the receiver is just like timing a muzzle brake.
You cut the barrel shoulder back the required amount to rotate the barrel into alignment in the receiver.
THEN you cut the tennon to length, cut the bolt nose counterbore and chamber to proper headspace.
 
Re: Short Action Customs: Timing curvature of the bore

now mark your tdc and remember how much tir there is at the muzzle. remove the barrel from the lathe and set it up again. is the tdc in the same spot? is the tir the same? if you loosen only the rear spider while the front is still tight. does the tir change at the muzzle change?

i have not done this yet but i am seriously wondering how much we are bending the barrel using the dual spider method and getting a false sense of true, stress free muzzle orientation. i'm guessing what we are doing is working since my personal rifles always seem to be within .75 moa of mechanical scope center on windage at 100 yards.
 
Re: Short Action Customs: Timing curvature of the bore

+1 on a video of barrel timing and the remaining cuts after the correct clock has been achieved.
 
Re: Short Action Customs: Timing curvature of the bore

300,

Take your tdc marked barrel that was done in the front and rear spider out of the lathe.

Then set the barrel up in your action truing jig using the screws, that you would use for a long action. Dial it in as normal with the adjusting screws. After dialed in you can look down the bore and see your high spot through the unsupported muzzle end.

You should be able to easily tell if the high spot is in the same spot visually.

This will answer your question if you are bending/stressing the barrel into true.
 
Re: Short Action Customs: Timing curvature of the bore

75 thousandths sounds seriously excessive to me, although i have not worked with that barrel manufacture before.

if my math is correct, in order to get .075" rounout at the muzzle of a 28" blank in the dual spider setup, that same barrel between centers would already have almost .0027" of runout in the first inch. that is unless we are bending that barrel...
 
Re: Short Action Customs: Timing curvature of the bore

We don't do gunsmith or barrel work but do have alot of parts gun drilled. The gun driller will not guarantee less than .002 per inch and is frequently much greater.

Hope this helps.
 
Re: Short Action Customs: Timing curvature of the bore

The run out thing has me wondering about threading the muzzle for a suppressor. Seems like the run out described above occurring in a short distance could be a bad thing when adding 8 inches of can on the end?
 
Re: Short Action Customs: Timing curvature of the bore

This would be the 1st intelligent argument that I have seen against the barrel nut system on my Savage, The runout is where it is when the chamber headspaces correctly. I'd been considering a traditional barrel install on my Savage receiver anyways and this pretty much seals the deal.
 
Re: Short Action Customs: Timing curvature of the bore

Dirty D, There are other things that I'm against on the Savage barrel nut system besides the timing thing. I set up all my Savages with out the nut.

The barrel nut is a excellent idea from a manufacturers point of view. Saves cost and time mostly.

Later, Frank
Bartlein Barrels
 
Re: Short Action Customs: Timing curvature of the bore

Holy crap.....I never would have thought a quality barrel is that un-straight.
 
Re: Short Action Customs: Timing curvature of the bore

If you guys think .075" is bad you should see what most normal firearms companies allow along with other barrel companies.

Also the way a barrel maker / gun company's manufacturing operations leading up to contouring of the blank can make the run out worse as well. It's not just drilling. They skip operations to save time/money or at times don't know about doing barrel manufacturing properly.

The old saying goes. You get what you pay for.

Later, Frank
Bartlein Barrels
 
Re: Short Action Customs: Timing curvature of the bore

This thread brings to light some of the reasons custom builders choose to work with certain barrel companies. Every barrel we work with gets all the information documented. Here is what we document, and these are some of the reasons why we stick with certain barrel manufactures.

We note how much barrel curvature each barrel we use has. This information gets computed into an excel spreadsheet where averages are formulated. This helps us see numbers that help make certain choices.

We also document barrel O.D. to bore runout on both ends and how well the barrel machines.

Accuracy of the barrel is not the only deciding factor for our barrel choices. We do not make "bandwagon" decisions on any part of our procedures or products. We are still a newer company, but we are doing our best to formulate our own techniques and procedures for executing our work. Short Action Customs never wants to be considered as an industry standard business building rifles based on what others do.

Good luck reading my chicken scratch!

Mark Gordon
Short Action Customs


IMG_5538.jpg


IMG_5539.jpg
 
Re: Short Action Customs: Timing curvature of the bore

Hey Mark! Thanks for adding to the post about how you keep data/information on the build etc....

Guys I tell everyone they should do this. I don't care if your doing the work yourself or a gunsmith doing the work.

This information could mean a lot down the road. If you have a problem somewhere during the build or after etc...and you should call us I always ask for the s/n of the barrel.

Glad to see the information Mark!

Later, Frank
Bartlein Barrels
 
Re: Short Action Customs: Timing curvature of the bore

Thanks for the the video It's a real eye opener. I have seen you make reference to timing the barrel for curvature but thaught you were talking about a couple thousandths not the ammount shown here.
shocked.gif


Stan
 
Re: Short Action Customs: Timing curvature of the bore

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RTK</div><div class="ubbcode-body">Once I saw a video of a barrel maker that straightened by hand all of their barrels after making them.
Is this not a common practice?? </div></div>

Just repeating this to see if any manufacturers in the US do this.
 
Re: Short Action Customs: Timing curvature of the bore

So the setup of that barrel is stress free and accurately depicts the straightness of the bore?
 
Re: Short Action Customs: Timing curvature of the bore

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RTK</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RTK</div><div class="ubbcode-body">Once I saw a video of a barrel maker that straightened by hand all of their barrels after making them.
Is this not a common practice?? </div></div>

Just repeating this to see if any manufacturers in the US do this. </div></div>

I saw a video of Ruger doing this.
 
Re: Short Action Customs: Timing curvature of the bore

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RTK</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RTK</div><div class="ubbcode-body">Once I saw a video of a barrel maker that straightened by hand all of their barrels after making them.
Is this not a common practice?? </div></div>

Just repeating this to see if any manufacturers in the US do this. </div></div>

The only current gun manufacturer that I know of that straightens barrels still is Savage. Not sure of any others.

i don't know of any custom barrel makers that do.

We won't straighten a barrel. Even straightening a barrel like a barrel that Mark shows in the video will still have runout. They are trying to straighten the bore of the barrel in different spots. Not necessarily at the muzzle etc...but when you straighten a bore of a barrel you induce stress back into the barrel blank. That barrel more often than not as it heats up from shooting you will notice your groups walk on paper. If you let the barrel cool and it starts printing where your first rounds where it's because the steel has a memory and wants to go back to where it started.

Later, Frank
Bartlein Barrels
 
Re: Short Action Customs: Timing curvature of the bore

Thanks for the answer
 
Re: Short Action Customs: Timing curvature of the bore

Fascinating stuff. I'm running my second Bartlein barrel now. Looks like I made a good choice.
 
Re: Short Action Customs: Timing curvature of the bore

Thanks for the vid.

How far apart do you feel your two indication points need to be to be sure that end it straight? Did you say 1" in the video?

Also, mind sharing your favorite long reach indicators?(anyone)

Im looking at a B&S
 
Re: Short Action Customs: Timing curvature of the bore

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Keith Johns</div><div class="ubbcode-body">
Also, mind sharing your favorite long reach indicators?(anyone)

Im looking at a B&S </div></div>

interapid 74.111965 and mitutoyo 513-504
 
Re: Short Action Customs: Timing curvature of the bore

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: M.Gordon</div><div class="ubbcode-body">This thread brings to light some of the reasons custom builders choose to work with certain barrel companies. Every barrel we work with gets all the information documented. Here is what we document, and these are some of the reasons why we stick with certain barrel manufactures.

We note how much barrel curvature each barrel we use has. This information gets computed into an excel spreadsheet where averages are formulated. This helps us see numbers that help make certain choices.

We also document barrel O.D. to bore runout on both ends and how well the barrel machines.

Accuracy of the barrel is not the only deciding factor for our barrel choices. We do not make "bandwagon" decisions on any part of our procedures or products. We are still a newer company, but we are doing our best to formulate our own techniques and procedures for executing our work. Short Action Customs never wants to be considered as an industry standard business building rifles based on what others do.

Good luck reading my chicken scratch!

Mark Gordon
Short Action Customs


IMG_5538.jpg


IMG_5539.jpg


</div></div>

it's pretty tough to impress me. this impresses me
grin.gif

keep up the good work.


edit: i don't see a spot for measured thread pitch diameter.
 
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