If shooting the same bullet, let's say a 70 grain Nosler Ballistic tip in a .243 Ackley vs a 6 XC. What sort of gain or loss would you expect from top end equal pressure loads

I don't know about a 70 grain bullet, but according to a resource I found a 107 grain will run +/- 95 ft/sec faster from the 243AI. That is measured from two rifles only and therefore is not a very broad spectrum to draw solid facts from, and they were loaded by two different hand loaders. Also two different barrels may not shoot equal velocity even when loaded identically.

The 6 XC factory load will send a 100 grain bullet out the muzzle around 2950 fps. The AI will beat that, by how much depends on the chamber pressure.

http://www.norma.cc/sv/Produkter/Jakt/6XC/Oryx/
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Usual to expect 1% velocity increase for every 4% increase in case capacity with all else being equal. Found this to be a good rule of thumb when comparing loads in my 2 x .243AI's to the standard .243.

quote:

Originally posted by Bushchook:
Usual to expect 1% velocity increase for every 4% increase in case capacity with all else being equal. Found this to be a good rule of thumb when comparing loads in my 2 x .243AI's to the standard .243.

Interesting rule of thumb there, thanks...

I'm experiencing a bit the opposite, however the sample of 2 is way to small to mean a thing.

quote:

Originally posted by 308Sako:

quote:

Originally posted by Bushchook:
Usual to expect 1% velocity increase for every 4% increase in case capacity with all else being equal. Found this to be a good rule of thumb when comparing loads in my 2 x .243AI's to the standard .243.

Interesting rule of thumb there, thanks...

I'm experiencing a bit the opposite, however the sample of 2 is way to small to mean a thing.

That isn't a rule of thumb that I invented. It can be applied to cartridges of all calibres, so if you're experiencing the opposite then there are likely to be other factors at play.

quote:

Originally posted by Bushchook:

quote:

Originally posted by 308Sako:

quote:

Originally posted by Bushchook:
Usual to expect 1% velocity increase for every 4% increase in case capacity with all else being equal. Found this to be a good rule of thumb when comparing loads in my 2 x .243AI's to the standard .243.

Interesting rule of thumb there, thanks...

I'm experiencing a bit the opposite, however the sample of 2 is way to small to mean a thing.

That isn't a rule of thumb that I invented. It can be applied to cartridges of all calibres, so if you're experiencing the opposite then there are likely to be other factors at play.

And like all rule of thumps, you will get occasions where it does not work.

I am not sure why, but have an idea that it might be due to the differences in barrels.

I had 5 identical Mannlicher Luxus rifles, all in 270 Winchester, and Norma 150 grain SP ammo.

We got about 150 fps difference in velocities between the fastest and slowest barrels!!??

Also, had a number smaller case cartridges - 300 RUM against the 30-378 Weatherby - that gave faster velocities.

Actions are just as individual too.

We have had some rifles that showed signs of high pressure with starting loads.

Other rifles would take several grains more powder over book maximum.

My best rule of thumb comes from the Hornady load book: each rifle is unique and generalizations should be made with circumspection.

Maybe some humans can tell the difference but I doubt that any animal could. As to trajectory it would be miniscule in the field...Usually the case in most of these discussions.

And then, some bbls are just plain "faster" or SLOWER than others, usually for some unkwown reason...

DM

So mutch guessing and spekulations.
There is no magig in why some barrels are faster or slower than others.
It all comes Down to internal dimentions, (boring dimentions, rifeling dimmention, length and angel of throat, eventual freebore, and chamberdimentions. Surfacequality also influence.
Often a pretty rough lapped barrels (gritt 180)(if the lappingroughness follows the rifeling) produces higher vel. than a highly polished barrel.
A large number of 6.5x55 barrels tested by Norma shoved thar systematically lapped barrels produced 40-140f/sek, higher vel. than in other wise identical hammerforged barrels. The higher vel. was acheved without increase in presure.

Just an interesting fyi:
The 'rule of thumb' has been said to derive from the belief that English law allowed a man to beat his wife with a stick so long as it is was no thicker than his thumb. In 1782, Judge Sir Francis Buller is reported as having made this legal ruling and in the following year James Gillray published a satirical cartoon attacking Buller and caricaturing him as 'Judge Thumb'. The cartoon shows a man beating a fleeing woman and Buller carrying two bundles of sticks. The caption reads "thumbsticks - for family correction: warranted lawful!"