Bored and reading shooting articles- barrel indexing

Brad Y · Post by **Brad Y** » Tue Jul 29, 2014 11:33 pm

Sitting at my brothers in Perth indulging in a few home brews and I've come across some articles by Gene Beggs regarding barrel indexing. Basically it appears to be finding the natural curve of a barrels bore and setting that at 12 or 6 o'clock so there is no tendency for a barrel to want to vibrate any other way than vertical when fired. This means the shooter tunes the vertical out as per normal and a high level of accuracy is achieved.

Sounds great in theory, has anyone tried it?

Quick · Post by **Quick** » Wed Jul 30, 2014 11:25 am

Talk to rimfire BR guys. I think that they do that as they cant really tune a load to the rifle except try different ammo.

DaveMc · Post by **DaveMc** » Wed Jul 30, 2014 11:31 am

You will find a lot of gunsmiths do this.

Brad Y · Post by **Brad Y** » Wed Jul 30, 2014 1:31 pm

Dave, no gunsmith I've ever used has done it that I know, but will talk to him when my next barrel arrives about doing it on this one. I'm no expert but it makes sense having the bore straight up and down not out to one side. The last thing I would want would be a barrel whipping with the tendency to throw shots sideways. Makes me wonder what my bad one is set like...

aaronraad · Post by **aaronraad** » Wed Jul 30, 2014 6:18 pm

Wouldn't be a simple process with a standard threaded barrel and action I would imagine :?:

I can see it being possible with a press fit type barrel like a rimfire or the old Steyr SSG 69 models.

Not sure about the pinned barrels or barrels using a Savage type nut if I understand them correctly. Maybe some of the clamp-fit interchangeable barrels as well but I think most of them have some sort or index machined into the end to assist correct location, let alone anything with fixed sights mounted on the barrel.

We'll be back to full-length stocks before you know it, test firing with copper/brass rings trying to identify the best point to pack the barrel's pressure points...like the armourers did with the old Enfield's.

Surprised I haven't seen any flanged linear bearings used in some forend of a tube-stocked F-Class rifle yet?

BRETT B · Post by **BRETT B** » Wed Jul 30, 2014 7:16 pm

Its not an easy process !!! There are 2 ways of doing it. You either need a threaded bushing between the action and barrell threads so you don"t effect headspace when you turn it to find the up down!! or you set the up down of the barrel and then re headspace with the reamer !!! Like i said not an easy process!!! There would also be a BIG margin for error as well if your Testing environment was not perfect to see if it shot better at 6 or 12 oclock compared to 3 to 9 oclock. You are also only assuming that the barrel has only one slender curve Too !! some may have more or be stightly twisted which would make it a guessing game on where to set it!!! You also need to consider if the outside contour or bend of the barrel is the same as the bore !!! It could also be thicker on one side compared to the other!! Just something to think about !!!

RDavies · Post by **RDavies** » Wed Jul 30, 2014 8:24 pm

[i]On a related subject. My main F class rifle has had around 15-16 barrels on it. The scope wind zero has remained pretty much in place for the lot. All of my good barrels have ended up with the wind zero being very close to the scope setting (some of the elevations settings have been a long way out), while any problematic barrels have nearly all had wind zeros a few moa out.
This seems to indicate that those barrels which were bent or vibrated to the side of the norm, were never great, never shot small groups, likely vibrating in a few planes, not just up and down.
It is not scientific at all, could be co-incidence, but I have started to get a good feeling when any barrel shoots very close to the usual wind zero and this has shown to hold true lately.
(The latest short mag barrel which MattP has just chambered shoots to the exact same wind and elevation zero as my current good 7mm, so I am optimistic about that one before getting to shoot a real group with it)[/i]

KHGS · Post by **KHGS** » Wed Jul 30, 2014 10:04 pm

RDavies wrote:[i]On a related subject. My main F class rifle has had around 15-16 barrels on it. The scope wind zero has remained pretty much in place for the lot. All of my good barrels have ended up with the wind zero being very close to the scope setting (some of the elevations settings have been a long way out), while any problematic barrels have nearly all had wind zeros a few moa out.
This seems to indicate that those barrels which were bent or vibrated to the side of the norm, were never great, never shot small groups, likely vibrating in a few planes, not just up and down.
It is not scientific at all, could be co-incidence, but I have started to get a good feeling when any barrel shoots very close to the usual wind zero and this has shown to hold true lately.
(The latest short mag barrel which MattP has just chambered shoots to the exact same wind and elevation zero as my current good 7mm, so I am optimistic about that one before getting to shoot a real group with it)[/i]

Actually it is surprising just how many of the name brand barrels have very straight bores. I am not convinced that barrels with slight bore curvature vibrate in any different manner than those without curvature, please note that I am referring to slight curvature & unstraightened barrels. If a barrel is well curved & is straightened all bets are off. In this case the vibratory patten would most likely be accentuated in the direction of the curve due to the stresses introduced by straightening. Indexing will not help, a shot out of the group vertically is just as bad as a shot out of the group horizontally, a 5 or worse is still what it is wherever it is. A barrel that will not shoot symmetrical groups has no place on any competition rifle.
Keith H.

williada · Post by **williada** » Wed Jul 30, 2014 10:47 pm

I make some general observations from barrel indexing I have played with in the distant past. While I think Gene Beggs indexer is great, I think it is best to make sure the first threads of the fitup are truly in contact between action and barrel as close as possible to the action face and the barrel shoulder. Discussion by Harold Vaughn on barrel joint in his book Rifle Accuracy Facts is worth a read. With Gene’s indexer the contact of the threads varies with each new position.

I have approached the task a couple of ways in the past in a four jaw chuck.

For those qualified, you can make a false receiver placed in the chuck out of steel or aluminium. Align it with dial gauges and to be sure it is perfect just face it off. Screw in the barrel which I assume it has been dialed in and threaded and chambered close to final limits correctly. Now the important bit, rotate the chuck by hand and with a dial gauge placed at the tailstock with only the gauge in contact with the barrel mark the 12 o’clock position.

Now you have to calculate how much the barrel will draw up to locate your mark in the correct position. To calculate how much the barrel will draw up in one turn you use the thread pitch. For a 1-12 thread pitch barrel, 1 divided by 12 equals 0.083” (imperial measurement). So if the barrel is within a quarter of a turn from going home, divide the full turn calculation by ¼ and allow 0.002” for crush and face off the shoulder. Eg. .083”/4=.020-.002”=0.018”. Now you re-chuck the barrel only, dial it in and nip up the chamber for correct headspace if you have to.

Or you could save time by taking the 12 o’clock measurement with the muzzle poking through the headstock when the barrel has been dialed in before threading and chambering. However this method can pose problems as the spider is released on the muzzle as to what is the true 12 o’clock position. You have to know what you are doing here. The former method given that not all actions are blueprinted is a surer bet and for all practical purposes will be good enough.

From my formal testing and for practical purposes usually the 12 or 6 position works best. This confirmed both the small bore experience and comments on US sites. One may be better at short range and the other may be better at long range. (Probably due to compensation characteristics as compensation can be induced at any distance). I will leave that to the sceptics to work out. In just a few barrels which waggle towards the muzzle, due to projectile torque effects, the position may vary a few degrees. Another diagnosis can be made from the target by making notes about the angular spread of shots and calculating the degrees it would take to shift that angle to the vertical then making the necessary adjustments on the barrel shoulder. If you are getting round or triangular groups don’t worry about changing anything. Most barrels are so well made the margins are not worth worrying about. But I have seen some shockers when placed in the chuck a visible wobble can be seen while looking down the bore. If you want to accentuate the angular spread vary the load a bit within a pet range of powder. A slightly vertical group is easy to tune with a tuner. It is those lateral groups or diagonal groups that need remedy if better ammunition does not seem to solve the problem.

The vertically indexed barrel also means the scope and bore line are aligned more appropriately. This is so important for windage and getting the most out of your scope adjustments not to mention you are closer to the optical centre of the scope. You can see this on the grid of an optical bore sighter. If the bore is not aligned with the scope then a different windage zero will result at each range. For those of us that use an outrigger in fullbore you know what I am talking about. Who needs another disadvantage in the range of factors that determine a score. Need I say more as Rod’s observations are correct.

For those that are worried about the variance in wall thickness as opposed to barrel curvature these crook barrels will show up as the barrel warms up and groups walk. On the other hand if the barrel profile has been turned down poorly then a grind between centres will help.

All of these procedures are very time consuming and costly. It would be a gunsmiths worst nightmare appeasing fastidious consumers. However, those smiths with the knowledge do it for themselves. Check out Gordy Gritters site on barrel fitting. It is not a level playing field, but the sooner it becomes one with this knowledge then the best shooter on merit will rightfully deserve the gongs.

Seddo · Post by **Seddo** » Wed Jul 30, 2014 11:46 pm

I have something to add on this one. My DTA uses a quick change barrel system and although not a popular F Class rifle shows this issue. All of the factory barrels are dialled in at the 12 o'clock position (if you believe them) and when i swap between factory barrels there is less than 2moa of adjustment required to re-zero. Now when i plug barrels that have been fitted by local gunsmiths the zero on 2 of them 4moa right and the other 12 moa left (not worrying about elevation for this one) of the scope zero with the factory barrel. The only way i can explain that is the curvature in the bore is not set at the same point on the locally made barrels as it is on factory barrels.

Any one have a better idea?

williada · Post by **williada** » Thu Jul 31, 2014 12:02 am

Seddo there is the possibility that your smith used a 3 jaw chuck on the re-enforce and the barrel therefore is not dialled in. So it would be that the threads/shoulder are not aligned concentrically with the bore. This occurs when the bore is off centre at the re-enforce. The three jaws grip the outside. Together with barrel curvature the problem is magnified. David.

pjifl · Post by **pjifl** » Thu Jul 31, 2014 7:11 am

To me a 12 min X discrepency is totally unacceptable. It indicates either a very poor barrel or poor workmanship and is unlikely to be very accurate. I would be redoing the shoulder which probably means a slight rechambering. It is very easy to do a shoulder between centres or equivalent in a lathe.

Peter Smith.

Seddo · Post by **Seddo** » Thu Jul 31, 2014 12:07 pm

Both barrels are super accurate, they just have a different point of aim.

KHGS · Post by **KHGS** » Thu Jul 31, 2014 1:47 pm

Seddo wrote:Both barrels are super accurate, they just have a different point of aim.

My point exactly....things are not always as they seem. It is great to have theories, but without proof they remain theories. My comments are based on many years of barrel fitting & observation of clients successes with what "won't work" in popular theory anyway. All of which tells me that the more we know the less we know.
Keith H.

pjifl · Post by **pjifl** » Thu Jul 31, 2014 4:00 pm

I am very surprised. And yes, theory is just that and may be wrong.

But it goes against a lot of what I have seen.

New barrels usually hit in or close to the black when carefully fitted and often well within the bull.

I would be trying to find out why the difference of 12 minutes if for no other reason than curiosity. There is knowledge to be gained by investigating any anomoly.

12 minutes left is so far off centreline that the scope wind setting will be well off centre to such an extent that the vertical range of the scope will be significantly reduced. It almost demands a different scope mount for that barrel.

Peter Smith.