Bore indexing

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Tim L
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Location: Townsville

Bore indexing

#1 Postby Tim L » Mon Nov 09, 2020 7:12 pm

OK so a bit of a plug for Matt Paroz to start.
Just had two new IBI barrels chambered ready to replace a 7 SAUM and the 6.5 SLR
5 round groups shot at 300 to find the powder charge followed by 5 round groups at 600 to find seating depth. No scope adjustment just shooting for groups
Both barrels show promise.
SAUM
20201109_185850.jpg

6.5 (only 4 cos Konsbergs lost a shot!)
20201109_185821.jpg


The point of the post, however, is to make an observation on indexing the bore to the action.
The old SAUM barrel came 2nd hand so not indexed to my action. Windage difference to the new barrel 3.5 minutes.
Both the 6.5s were chambered by Matt for my action. Windage difference between the barrels, bugger all!
Food for thought if your smith says it doesn't matter.
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Last edited by Tim L on Tue Nov 10, 2020 9:41 am, edited 1 time in total.

Steve N
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Location: Gippsland Victoria.

Re: Barrel indexing

#2 Postby Steve N » Mon Nov 09, 2020 7:32 pm

Tim I had a barrel that tracked horizontally further right with increasing velocity instead of vertically as would normally be expected with a properly indexed barrel. Was supplied and nstalled on the action by a very respected gunsmith. (Not Matt or any other that contributes to this forum). Had some interesting ladder tests.
.

Tim L
Posts: 655
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Re: Barrel indexing

#3 Postby Tim L » Mon Nov 09, 2020 7:39 pm

Steve N wrote:Tim I had a barrel that tracked horizontally further right with increasing velocity instead of vertically as would normally be expected with a properly indexed barrel. Was supplied and nstalled on the action by a very respected gunsmith. (Not Matt or any other that contributes to this forum). Had some interesting ladder tests.
.

Bugger, not even thought about that!

Gyro
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Location: New Zealand

Re: Barrel indexing

#4 Postby Gyro » Tue Nov 10, 2020 4:12 am

‘Indexing’ the barrel makes absolutely total sense to me. It takes longer to do and more skills are required to achieve it, both of which translate to more cost to get it done. Some say the gun will never ever shoot consistently if the barrel is not indexed !! That may or may not be true but it makes total sense to me that it is a better way.

Of course some like to be ‘snobby’ about this topic, as if it was rocket science. It aint. Have your barrel fitted by someone who you KNOW will take the time and attention required to do it properly and to a high standard. I do my own so I know that part is perfect.

Pommy Chris
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Joined: Tue Oct 21, 2014 12:05 pm

Re: Barrel indexing

#5 Postby Pommy Chris » Tue Nov 10, 2020 7:25 am

I am sure Peter Smith will jump in, but as far as I am aware he never bothered with indexing and his barrels were all tack drivers. My best barrels I can swap on any of 4 actions with same load, indexing is different on all actions and it makes no difference at all to the load.
Chris

Rich4
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Location: Chinchilla

Re: Barrel indexing

#6 Postby Rich4 » Tue Nov 10, 2020 8:40 am

Steve N wrote:Tim I had a barrel that tracked horizontally further right with increasing velocity instead of vertically as would normally be expected with a properly indexed barrel. Was supplied and nstalled on the action by a very respected gunsmith. (Not Matt or any other that contributes to this forum). Had some interesting ladder tests.
.

I would suggest that is related to stress retention more so than indexing, whilst you should retain centre by indexing with my preferred process, vertical zero is then dependent on bore curvature

pjifl
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Location: Innisfail, Far North QLD.

Re: Barrel indexing

#7 Postby pjifl » Tue Nov 10, 2020 10:00 am

Don't forget that barrels have improved so any gain from indexing is much less than it used to be.

So what does the accepted wisdom say about reasons for indexing.

1/ Barrel changing is less confusing when indexed. 30 years ago, usually after a barrel change, zero was within 2 minutes but now it seems to me with with newer barrels it is well under 1 minute. It is nice to know when changing a barrel that the wind horizontal setting has minimum change because it can be very hard to rezero for wind while competing on a range and this does really matter. Rezeroing for elevation is relatively simple to do.

2/ Vibration analysis is less confusing if you know induced vibration will be entirely in the vertical plane. Some take this to extremes assuming vertical indexing is essential. But locking lugs always have an influence. And asymmetrical aspects of an action like port cutout and bolt handle should mandate something different from vertical indexing. No one bothers about this which suggests to me that 'perfect indexing' does not exist anyway.

I have always been more interested in having perfect headspace matching of different rifle's chambers. Perfect headspacing and perfect indexing on paper is easy - a lot more tedious in practice.

If you feel that by indexing you have an advantage then I am sure this will be true.

Peter Smith.

Matt P
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Re: Bore indexing

#8 Postby Matt P » Tue Nov 10, 2020 2:03 pm

Thanks Tim, glad those barrels are looking good.
It really depends on how the barrel is dialed in as to if indexing is required. I'm not going to go into the how or why, not because it's a secret but because it usually ends up in a pissing match of "my way's better".
Matt P

Gyro
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Location: New Zealand

Re: Bore indexing

#9 Postby Gyro » Tue Nov 10, 2020 2:48 pm

Aint that the truth ! Your comments Matt suggest - to me at least - that some barrels will benefit from indexing. I would say “of course they farking will”, at least from a purely mechanical stand point.
But then Peter alludes to action and/or bolt lug ‘asymmetries’ ……. and on and on it goes.
Just win the shoot. Aint that the whole point ? Never mind the waffle about my gun does this and bla bla bla. I’m bored.

cheech
Posts: 202
Joined: Wed Jul 15, 2009 11:10 pm

Re: Bore indexing

#10 Postby cheech » Tue Nov 10, 2020 3:12 pm

Matt P wrote:Thanks Tim, glad those barrels are looking good.
It really depends on how the barrel is dialed in as to if indexing is required. I'm not going to go into the how or why, not because it's a secret but because it usually ends up in a pissing match of "my way's better".
Matt P


Just keep doing what it is you do mate , that swan barrel / Norma you did for me printed a 0.3 moa group for the last 4 shots (1.2gn spread ) at 900 during a ladder test

KHGS
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Re: Bore indexing

#11 Postby KHGS » Tue Nov 10, 2020 6:34 pm

Matt P wrote:Thanks Tim, glad those barrels are looking good.
It really depends on how the barrel is dialed in as to if indexing is required. I'm not going to go into the how or why, not because it's a secret but because it usually ends up in a pissing match of "my way's better".
Matt P




Ain't that the truth ??? =D> =D> =D> =D> =D> :lol: :lol: :lol: :lol: :lol: :lol: !!!!!
Keith H.

williada
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Re: Bore indexing

#12 Postby williada » Tue Nov 10, 2020 6:49 pm

Bore indexing works. Some barrels that don't respond to proper fitting may have a bore that wanders within the profile and so the wall thickness can vary. As things get hotter shots tend to walk or you may get a twitch or a squeeze near the muzzle depending on what harmonic you are using which determines where the muzzle points.

Rich4
Posts: 287
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Location: Chinchilla

Re: Bore indexing

#13 Postby Rich4 » Tue Nov 10, 2020 8:59 pm

Matt P wrote:Thanks Tim, glad those barrels are looking good.
It really depends on how the barrel is dialed in as to if indexing is required. I'm not going to go into the how or why, not because it's a secret but because it usually ends up in a pissing match of "my way's better".
Matt P

I don’t think anyone would argue that you’ve got a technique that works, and unwillingness to participate in the aforementioned competition definitely stifles discussion, personally indexing to the vertical plane is a no brainer to my understanding of the principles

Matt P
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Re: Bore indexing

#14 Postby Matt P » Tue Nov 10, 2020 9:47 pm

Rich4 wrote:
Matt P wrote:Thanks Tim, glad those barrels are looking good.
It really depends on how the barrel is dialed in as to if indexing is required. I'm not going to go into the how or why, not because it's a secret but because it usually ends up in a pissing match of "my way's better".
Matt P

I don’t think anyone would argue that you’ve got a technique that works, and unwillingness to participate in the aforementioned competition definitely stifles discussion, personally indexing to the vertical plane is a no brainer to my understanding of the principles


Over the years I’ve tried many different methods (except the steady rest method) and this method has given me the most consistent results.
When “dialing in” a barrel you can only dial in two points. Some choose to dial in the muzzle and the throat/breech (many, many winning barrels have been done this way) this method doesn’t require indexing as the muzzle “runs true”.
I prefer to dial in forward of the throat and the back of the barrel (I have a long stem dial indicator and indicate directly on the lands/groove, no range/Grizzly rods), now when those two points are dialed in the muzzle will runout which requires indexing.
Barrels aren’t straight and with the long stem indicator you really see how much the bore “moves around”. My method (in my opinion) allows me to align the centre of bore in front of the throat and the back of the chamber so the reamer follows “as straight a hole as possible”.
I index the barrel to 12 o’clock, no science as to why other than most of my builds are long range and pointing to 12 o’clock gains a few MOA and keeps the windage close to the middle of the scopes adjustments.
The other benefit I’ve seen (bore scope) and measured ( I always check alignment after reaming) is the throats are always centred.
Matt P

bruce moulds
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Re: Bore indexing

#15 Postby bruce moulds » Wed Nov 11, 2020 6:03 am

my instinct would be to go for 6.00 o'clock.
bruce.
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