Change of POI between different bullets.

[TStone]

Many people will say a barrel tuner, and I would disagree.
You see you can try and tune the load to shoot at a different place, however then you will alter the POI of the other load again, the one against which you are trying to bring it to.
With rifles like these it's good old fashion pen and paper, 10 clicks left and 12 clicks right for X bullet, zero for default load.

Sure, and with a decent scope that is not a problem but I would like my 6mm to shoot Vmax and CX bullets to the same point of impact so that I could use the cheaper Vmax for dealing with jackal and crows and drop a CX into the chamber when I want to kill something bigger and tougher. But that is really just a want, not an important need.

[Againstthegrains]

Sure, and with a decent scope that is not a problem but I would like my 6mm to shoot Vmax and CX bullets to the same point of impact so that I could use the cheaper Vmax for dealing with jackal and crows and drop a CX into the chamber when I want to kill something bigger and tougher. But that is really just a want, not an important need.

To get that right, would take a considerable amount of luck. The metal from the CX is most likely turned from pure copper and the cup of the Vmax most likely pressed from a sheet of gilding metal (Copper with 5% Zinc). They have different physical properties and are likely to interact with the barrel differently. Some people have reported a need to clean the gilding metal from a barrel before shooting mono's as this can affect accuracy, so switching between these two bullets without cleaning may not be the best idea.

[Againstthegrains]

Thanks, I understand this. What I do not understand is why there are such huge differences between different rifles, even rifles made by the same manufacturer.

If you ever have time and money to entertain your curiosity, I would be interested in a ladder as described my Messor using 3 distinctly different bullets from both rifles, to see what the maximum spread is like, from both rifles. This would be a better way of measuring and comparing 2 barrels, rather than comparing the 3 best loads.

[TStone]

If you ever have time and money to entertain your curiosity, I would be interested in a ladder as described my Messor using 3 distinctly different bullets from both rifles, to see what the maximum spread is like, from both rifles. This would be a better way of measuring and comparing 2 barrels, rather than comparing the 3 best loads.

That would be the way to do it but, as you mentioned, it will take both time and money. It would make an interesting project.

[AJR]

Small caliber projectiles might realize a similar POI as distinctly differing ones when discharged from the same barrel at different speeds, but such a result will probably be limited to a shortish distance, and to specific rounds. It will not hold true to 1000m, or beyond.

Although the transaction between pressure, projectile and barrel is complicated, the paterrning effect at a given distance is probably the result of the interaction between the projectile's bearing surface, its elasticity, the barrel's composition and volume, OBT, rifling, and the pressure curves under which the transaction is effected. The strange 'similar patterning' is not dark magic, but a repeatable result at a fairly short distance, where the projectile, barrel and propellant's transaction remains within a given set of parameters.

Over time the result will differ / drift, with everything returning to natural chaos, and eventually, nothingness.

Small differences - such as differing headspace / chamber size / barrels / actions - will introduce a new set of parameters, unique to that rifle.

[Heath Robinson]

I'm just wondering whether the phenomenon could be caused by resilient stresses in the barrel.
If so, Cryo treatment could solve it.
But then again, I don't know if anybody does cryo treatment locally.

[tcbc]

Is the difference between rifles not related to bullet jump, into the lands. The lead? If the action isn’t completely true to the barrel and/ or the bolt face not square, I think that different bullets with different ogives will set up differently in the rifling. Which may cause the variation in barrel vibration point leading to variable exit vectors.

It’s probably worth having the bolt lugs trued, checking that the bolt face is square and that the action is aligned to the barrel.


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[Againstthegrains]

Is the difference between rifles not related to bullet jump, into the lands. The lead? If the action isn’t completely true to the barrel and/ or the bolt face not square, I think that different bullets with different ogives will set up differently in the rifling. Which may cause the variation in barrel vibration point leading to variable exit vectors.

It’s probably worth having the bolt lugs trued, checking that the bolt face is square and that the action is aligned to the barrel.

That makes a lot of sense. I was always under the impression that blueprinting was done to improve the accuracy of a rifle, but never considered it to also reduce the variation of POI's of different bullets.

Do you have any before and after experience with this?

I was thinking of doing this straight off the bat with a new rifle, but am wondering if the 7k quote I got is worth it?

[Heath Robinson]

I was thinking of doing this straight off the bat with a new rifle, but am wondering if the 7k quote I got is worth it?

From the point of view of the amount of work it takes to do it PROPERLY, I think R7k is reasonable.
Whether it's worth it will depend on the accuracy of the rifle and the requirement you have for it. I wouldn't do it without shooting the rifle first. Shooting it doesn't make the blueprinting process any different.

Unless it's a custom rifle built from components. Then nothing I said above is valid. But I would sort-of expect all the steps to be done as part of a custom build.
Of course, there's never a guarantee that any of the steps will be done right.

[tcbc]

That makes a lot of sense. I was always under the impression that blueprinting was done to improve the accuracy of a rifle, but never considered it to also reduce the variation of POI's of different bullets.

Do you have any before and after experience with this?

I was thinking of doing this straight off the bat with a new rifle, but am wondering if the 7k quote I got is worth it?

No current estimate. I had my Musgrave RSA trued over 20 years ago and it was about R500 or so. A gunsmith in Durban who used to work on Bisley rifles. The barrel was already well aligned to the action but the bolt face and locking lugs needed a polish. In those days we competed with issued ammo, and having the rifle blueprinted made a difference in ammo consistency.


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