Gunsmithing Barrel runout question

[tlg308]

Trying to get some experience to test a theory.. In regards to the top barrel manufacturers, what is the common runout in the bore you’ve seen at the muzzle end when the barrel is dialed in at the chamber end? I understand all barrels regardless of manufacture have somewhat of curve in the bore.

My current lathe has too long of a headstock to check the runout at the muzzle. I wish I had the resources to buy 15 barrels and test this myself.

Just trying to get a little data. If you want to pm rather then post, due to thinking people who don’t understand all barrels have a curve will see this and think negatively of the manufacturer feel free.

Thanks

 

[tlg308]

Just the bore, since my understanding is the OD of the barrel itself will always be a little off the bore since drilling a 27” hole will never be dead center in the barrel in relation to the OD

So when the bore at the chamber end of the barrel is completely dialed in, how much runout is seen/measured in bore at the muzzle end is what I’m curious about.

 

[308pirate]

Trying to get some experience to test a theory.. In regards to the top barrel manufacturers, what is the common runout in the bore you’ve seen at the muzzle end when the barrel is dialed in at the chamber end? I understand all barrels regardless of manufacture have somewhat of curve in the bore.

My current lathe has too long of a headstock to check the runout at the muzzle. I wish I had the resources to buy 15 barrels and test this myself.

Just trying to get a little data. If you want to pm rather then post, due to thinking people who don’t understand all barrels have a curve will see this and think negatively of the manufacturer feel free.

Thanks

Runout measurements require a reference datum. Which part of the barrel would you like to use as one?

 

[Hoyt7mm]

If I understand your question correctly, the muzzle end is usually less than .025" but I've seen as much as .040"

I haven't seen a difference in performance on target though

 

[308pirate]

Just the bore, since my understanding is the OD of the barrel itself will always be a little off the bore since drilling a 27” hole will never be dead center in the barrel in relation to the OD

Nothing is ever dead center or dead on every single time.

 

[308pirate]

If I understand your question correctly, the muzzle end is usually less than .025" but I've seen as much as .040"

Again to what datum? How is the barrel held? How it's held has a huge influence on the indicator reading.

 

[Hoyt7mm]

Again to what datum? How is the barrel held? How it's held has a huge influence on the indicator reading.

I'm assuming the chamber end is held in a chuck and indicated in to lathe centerline like it would be for chambering

 

[Rubicon Precision]

If you read the internet, one would think the bore would run out a few inches because these barrel makers have no idea how to gun drill a deep hole…

 

[tlg308]

If I understand your question correctly, the muzzle end is usually less than .025" but I've seen as much as .040"

I haven't seen a difference in performance on target though

Cool that’s what I was curious about. Thanks.

 

[E. Bryant]

Again to what datum? How is the barrel held? How it's held has a huge influence on the indicator reading.

*Takes deep breath, ponders posting a semi-snarky rhetorical question about datums vs datum features, goes back to geometry problems I'm paid to solve*

 

[parshal]

I indicate the bore in the headstock so it's straight between two spots at the throat. Drilling a straight hole to that spot before running the reamer should ensure the bullet is straight in the throat. I then tighten the spider on the outboard side to keep the barrel from flopping loosely. Many barrels set up like this have the muzzle side way, way off which is easily visible as the lathe spins. I don't measure it because it's straight where I'm concerned, at the throat.

I'm not sure that answers the OP's question but I don't believe it matters when set up like above. I believe Gordy's process does indicate the muzzle side.

 

[308pirate]

*Takes deep breath, ponders posting a semi-snarky rhetorical question about datums vs datum features, goes back to geometry problems I'm paid to solve*

I didn't (and still dont) feel like teaching an online GD&T class

 

[tlg308]

Thanks @parshal I appreciate the feed back. I think Gordy used to do that but now seems to be dialing in the throat like you do.

Using that method is what I was curious about how much runout in the bore at the muzzle end would be.

Again I know that doesn’t effect accuracy I just wanted a little data to try this theory I’m testing with my lathe. I’m working on dialing in a portion of the bore at one point (i.e. throat portion) and calculating an estimate of runout at different locations within the bore from breach to muzzle.

 

[Shooter71]

When you’re done collecting data and testing theories and calculating stuff.... put some loaded ammo in the lathe and run some more tests and calculations, and report back. You might be surprised to find we’re shoving some pretty crooked stuff into relatively less crooked holes.

 

[Rubicon Precision]

Again I know that doesn’t effect accuracy I just wanted a little data to try this theory I’m testing with my lathe. I’m working on dialing in a portion of the bore at one point (i.e. throat portion) and calculating an estimate of runout at different locations within the bore from breach to muzzle.

There’s way too many variables to calculate this. Every barrel is different. Depending on how the barrel is held in the lathe, it may be being bent between chucks/spiders to force a reeding that may not be reality in the free state. Working between chucks/spiders, one may think they have .040” TIR at the muzzle with the chamber end “dialed in”, tear down the whole setup and redo it to find .020” TIR at the muzzle 180 degrees out from their first set up.

 

[chevy_man]

Thanks @parshal I appreciate the feed back. I think Gordy used to do that but now seems to be dialing in the throat like you do.

Using that method is what I was curious about how much runout in the bore at the muzzle end would be.

Again I know that doesn’t effect accuracy I just wanted a little data to try this theory I’m testing with my lathe. I’m working on dialing in a portion of the bore at one point (i.e. throat portion) and calculating an estimate of runout at different locations within the bore from breach to muzzle.

You're chasing your tail at that point.

True the chamber to the bore at the chamber end. What the bore does at the other end doesn't concern the chamber.


If you try chasing the muzzle you'll never get anywhere past frustrated.

 

[iceng]

You will have more fun learning which barrel is cut rifled VS button rifled. Then you can look into pull button VS push button. Dont forget hammer forged barrels.

Pro tip: barrel warping is majority from heat treatment, and the grain structure of the barrel pre / post.

In order to have usable data from this, you will need a huge sample set, and in order to correctly measure this (repeatedly) your equipment may not be up to the task.

Lastly, as @Shooter71 stated, ammo is a huge variable which often is out of the barrel makers, and gunsmiths control.

Theres some great information here. @Feniks Technologies can help with organising stats, @Frank Green can teach you about barrels and their construction (and acceptable runout) and @308pirate can make you question your will to live. That and explain how torque values on barrel tension are another variable in accuracy.

 

[Wannashootit]

If you try chasing the muzzle you'll never get anywhere past frustrated.

I think he's referring to "clocking" the bore runout to 12:00 when the barrel is torqued in place.
I generally don't go that extra step, but it's simple enough to set the barrel shoulder where it's needed to do that after using a gage pin in the muzzle to locate, just like clocking a brake on the muzzle.

 

[Fanadex60]

I think he's referring to "clocking" the bore runout to 12:00 when the barrel is torqued in place.
I generally don't go that extra step, but it's simple enough to set the barrel shoulder where it's needed to do that after using a gage pin in the muzzle to locate, just like clocking a brake on the muzzle.

 

[gigamortis]

We all seem to understand the reality that drilling a 26"+ deep hole in a piece of bar stock will result in some wandering off center. It would make sense to start with an oversized OD barrel blank and set it up between centers. Cut whatever barrel contour you want on the outside and it will then be concentric to the bore.

 

[Rubicon Precision]

We all seem to understand the reality that drilling a 26"+ deep hole in a piece of bar stock will result in some wandering off center. It would make sense to start with an oversized OD barrel blank and set it up between centers. Cut whatever barrel contour you want on the outside and it will then be concentric to the bore.

What’s to say the contouring process doesn’t move the relationship between the OD and bore?

 

[iceng]

Spinning the barrel blank VS spinning the drill alao gives different results.

Nextly, contouring of the barrel is done after drilling / rifling, and held between centres (usually), or a drive dog / spider. This helps make the ENDS concentric.

 

[E. Bryant]

Spinning the barrel blank VS spinning the drill alao gives different results.

As does spinning both.

 

[iceng]

Good point, i should have mentioned that.

 

[308pirate]

We all seem to understand the reality that drilling a 26"+ deep hole in a piece of bar stock will result in some wandering off center. It would make sense to start with an oversized OD barrel blank and set it up between centers. Cut whatever barrel contour you want on the outside and it will then be concentric to the bore.

Not necessarily. The bore has to be straight within very few thousands of an inch for what you say to be true.