Barrel indexing vs muzzle jump

[holstil]

It amazes me that we are able to get barrels as straight as we do. I've drilled many holes and sizes in lots of types of steels and materials with different devices. These gun drills do an incredible job in my opinion. Drills with oil ports in them are cool. Drilling through 28" plus of steel holding the tolerances they do is some feat.
A lot of questions would be answered if you looked down an indicated barrel from both ends while it's spinning. Then you might want to consider what the relationship of the od to the id is at any given point. Leaving out any difference in lands variance. There could be a mean off center to be indexed, would that offset the mean of the od? Food for thought.
I give a barrel three chambers about 70* apart before I scrap it. Sometimes they just shoot after a rechamber maybe its due to what is being discussed or probably there is much more that I don't understand.

 

[holstil]

Finding good bullets is a higher priority for me.

 

[butchlambert]

Ok how do we straighten cam bore and main on race motors
Sunken home
The problem with cam you then have to get over size od bearings
Main bearings you can cut the caps and then you don’t need oversized od bearing
Yes it will straighten the bore .

Larry,
Check with the Sunnen company. I've cut a few main bearing bores, then you hone them. You do not cut them with a hone.
Don't take my word, search or call the right people. I've already done the checking.

 

[ireload2]

Try not to take the silly replies to heart. alinwa responded in the thread earlier, shoot him a PM.. he does a TON of testing of this stuff. I also think what Mr Lambert mentions has merit, that it may be better to think of the barrel as more of "twisted banana" or spiral to it than just a one dimensional curvature... dmoran also Id bet has useful insight on the subject.. Benchrest central honestly might give you better responses

It also depends on the direction you are shooting since the spin of the earth on its axis influences the flight of the bullet.

 

['Freak]

http://riflebarrels.com/barrel-making/

http://riflebarrels.com/what-makes-a-rifle-barrel-accurate/

http://riflebarrels.com/a-look-at-the-rigidity-of-benchrest-barrels/

“… When a cartridge is fired in a chamber, the barrel undergoes many stresses. It begins to vibrate when the firing pin starts its fall and these vibrations increase dramatically from then on.

During recoil and while the bullet is still in the barrel, the barrel will whip vertically. This happens because the thrust axis of the rifle is above the centerline of the stock.

During recoil the barrel comes back and up. The muzzle will lag behind the rest of the barrel in this movement and the vertical whipping motion is set up. While these vibrations of the barrel are very small, they do exist….”

&&

Think about what’d happen to vertical whip with the muzzle end also clocked towards one side or the other …

‘’ … The stiffer a barrel is, the less the muzzle will jump around. This brief description is of course an oversimplification of the dynamics that take place, but they do point out the type of barrel movements occurring and why a stiffer barrel is more accurate. …”

 

[Alex Wheeler]

Most of what we "know" about barrel harmonics is educated guesses. Its just a very hard thing to measure. Like most things in shooting you have to test on paper. Results tell the story. For some, things like this may be a joke. But I am glad there are people who are interested in testing things otherwise we wont make any progress. As soon as it comes down to barrels and bullets, I'll be bored with it. I have never found a barrel with a perfectly straight bore. I dont think it is possible to drill one that good. I do have one out there that is as straight as it gets. Waiting for test results on it. So far I have seen absolutely no correlation between bore straightness and accuracy. I am a believer in positive compensation, harmonics and recoil pulse play a big role it that. Indexing barrels is something I do.

 

[Terry]

What about Savage actions . How do you index the barrel on them ? Don't you just screw the barrel in until the headspace is correct ? What if your index point is a 1/2 turn either way ? I'd assume you would want to remove material rather then add shims ?

Without the nut you index them as you would any other. You can accomplish this with the nut if you have to, but it's more work.

 

[seymour fish]

So just think barrel harmonics. Internal ballistics. Barrels are not straight. If the muzzle of the banana barrel is pointing down will the rifle recoil straighter back or not? Think that it is a f class rig or a benchrest rig?

Gregorio, what if the bent bbl constitutes a spring, which if indexed at 6 o clock will whip upward into that spring, thus making the positive compensation node narrower for long range application

 

[savagedasher]

Larry,
Check with the Sunnen company. I've cut a few main bearing bores, then you hone them. You do not cut them with a hone.
Don't take my word, search or call the right people. I've already done the checking.

You cut them so you can have a small enough hole to when you hone the they aren’t over size

 

[UltraBR30]

You cut them so you can have a small enough hole to when you hone the they aren’t over size

Wondering where your getting this information from. What barrel makers are drilling bores small and honing them out to diameter as you state?
Phil

 

[Alex Wheeler]

Honing is a nice addition to the process, but in no way can it straighten a bore. To straighten a bore would require a hone the length of the barrel and made of some material rigid enough to prevent any flex of the hone. Basically an impossibility. One of the best shooting barrels I ever owned had a loose spot just in front of the chamber. It was bad enough you could feel it with a brush, didnt even need a slug. That barrel may have been the best dasher I ever had. It would collect carbon fowling in that loose spot and was a pain to clean. But man it shot. I still dont know of a way of even remotely telling how a barrel will shoot until you shoot it. If I would have slugged that barrel and nit picked it, no doubt I would have sent it back and missed out on a excellent barrel.

 

[338 Mollett]

Very good points Alex !

 

[fgregorio]

Hi all, I've done the testing in regards to barrel indexing.
2 identical barrels: .308 Bartlein 30" 1/11 5R
Barrel 1: muzzle is 15 thou off centre from tenon.
Barrel 2: muzzle is 25 thou off centre from tenon.
Both barrels indexed to 6 o'clock.
Both barrels have the exact same wind zero.
Barrel 1 impacts 1.5 moa higher than barrel 2 in elevation zero using the same iron sight for both. This is how I know the different elevation zeros and the identical wind zeros.
Muzzle jump?
Much less for 2 reasons:
1- index to 6 o'clock?
2- both are left twist barrels and I am left handed (sling and irons). Having the recoil twist into my position is a major game changer.
So this one is still open for discussion.
Tuneability of the rifle?
These are by far the two most precise barrels I've ever had. I've had other Bartleins, Kriegers, Tru Flutes, but nothing like this. I had to input elevation and windage to separate groups inside the ladder test.
Otherwise the node would be just a ragged hole at 300m (varget from 47.4gr to 47.9gr is the node).
Barrel tuner wise, the tuning nodes are far wider and more neutral than anything I've ever seen.
So, yes, there is curvature in a barrel and its advantageous to have that curvature point either up or down.

 

[21shooter]

Alex Wheeler, Dec 20, 2017 Report
#53 Like Reply
holstil and Ledd Slinger like this.
ng is a nice addition to the process, but in no way can it straighten a bore. To straighten a bore would require a hone the length of the barrel and made of some material rigid enough to prevent any flex of the hone. Basically an impossibility. One of the best shooting barrels I ever owned had a loose spot just in front of the chamber. It was bad enough you could feel it with a brush, didnt even need a slug. That barrel may have been the best dasher I ever had. It would collect carbon fowling in that loose spot and was a pain to clean. But man it shot. I still dont know of a way of even remotely telling how a barrel will shoot until you shoot it. If I would have slugged that barrel and nit picked it, no doubt I would have sent it back and missed out on a excellent barrel.

A Bit Too Much Info That's what those foot long reamers are for

 

[jrm850]

Interesting coincidence... I quit participating on this site a good while ago, partly because of a reaction to this very topic. I check in today, and what topic pops up? lol. It's good to see that there is positive conversation this time though. I appreciated reading through this thread and especially the sharing of empirical results. Cheers all. Back to occasionally lurking for me.