Is Ackley an improvement? Tikka compatible?

C.W. Richter

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anything on the 7x57 and 250/300 parent cases will have a big gain due to a significant gain in case capacity when the outdated taper is blown out of them on fireforming.
the 308 will gain far less percentage wise.
there are those who claim that the smaller capacity cases can beat the bigger capacity due to being more efficient or some other such tripe.
i recall one who told me that the 250/3000 ackley is faster than the 25/06 ackley because it is more efficient.
case shape is irrelevent to velocity, but capacity is relevent..
as long as you use the correct burning rate powder for the job.
the 7x57 ackley has close to the same capacity as the std 280 rem.
translated into english, at the same pressure and with the best powder, velocities will be the same.
if you want to have to fireform cases for std 280 velocities, go ahead and do the extra work, buy the more expensive dies, and burn out a barrel sooner.
the 280 ackley will be between the std 280 and the 7 rem mag, because it is between them in case capacity.
as a straight dingo gun it would shoot pretty flat with 120 gn vmax or the bit harder 120 gn sierra soft point.
140s of different construction offer a wide range of game opportunity with the same zero and shooting nearly as flat.
then up to 160s of various construction.
after that you have a 375.
such a rifle with a 24" shilen no 3 profile barrel or similar will do a lot of jobs very well.
fir a pure dingo only gun, a 25/06 or a 6mm ackley rem might suit more, but are very specialized.
the 280 or 280 ackley are just so versatile.
120 gn bullets have sectional density of 50 gn 30 cal.
140s the same s.d. as 165 gn 30 cal.
160s the same as 190s.
a nice compromise.
bruce.
Agreed but case shape does affect velocity. Familiarize yourself with the Venturi effect... Ackley's shoulder and neck expound upon this. Otherwise you wouldn't see the tremendous velocity gains in cases containing 10 grains less powder.
 

bruce moulds

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Agreed but case shape does affect velocity. Familiarize yourself with the Venturi effect... Ackley's shoulder and neck expound upon this. Otherwise you wouldn't see the tremendous velocity gains in cases containing 10 grains less powder.
not true.
equal pressures with the right burning rate powders, equals same velocity, whatever the case shape.
tests have been done on this.
where the venturi theory came from was none other than the great roy himself, with his double radius shoulders.
the main advantage of ackley cases, other than the gain in velocity over their paret due to increased capacity, and no other reason, is that case life is extended.
another thing is that the 40 degree shoulder directs flame onto the neck, rather than the throat/leade, an aid to barrel life.
bruce.
 

CBH Australia

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Agreed but case shape does affect velocity. Familiarize yourself with the Venturi effect... Ackley's shoulder and neck expound upon this. Otherwise you wouldn't see the tremendous velocity gains in cases containing 10 grains less powder.

not true.
equal pressures with the right burning rate powders, equals same velocity, whatever the case shape.
tests have been done on this.
where the venturi theory came from was none other than the great roy himself, with his double radius shoulders.
the main advantage of ackley cases, other than the gain in velocity over their paret due to increased capacity, and no other reason, is that case life is extended.
another thing is that the 40 degree shoulder directs flame onto the neck, rather than the throat/leade, an aid to barrel life.
bruce.
Getting way above my level knowledge now.
Out of curiosity does anyone know if the technology exists to look, see or measure what is happening when a given round is fired in test conditions. Can the model or illustrate the actual start and flow of the pressure as the combustion takes place or is it a theory?
Can the expansion and flow of the gas be shown on a diagram or such a thing in a way that shows various points (time lapse) in the minut point of time it takes.
I can understand Bruce point about the direction of gas flow and escaping gas pressure perhaps being more direct than directed at the throat but it would be interesting to see if it can be measured and animated as a way of showing the degree of efficiency and the effects of case design.
It’s interesting stuff and I see Roy Weatherby died in 1988 presumably retired sometime earlier. Technology has advanced in many fields, cartridge development might not be leading that race but I assume the technology to assist it has.

Quite keen on the cartridge and I will possibly see it through now I have mentioned it to my wife.
 

colorado

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So your H4831 is Made here as AR2213sc. Repackaged in the US buy Hodgdon.
I’ve read on a forum that a 22” barrel won’t be long enough for a full burn off of this powder.
I simply don’t know, I’ve read plenty but and loaded lots but still not in the league of many here with experience or a chronic at this point.

Copied from my thread
It seems that the Australian ADI powders don’t seem to be the best options for .280ai. Their book velocities are way lower than what some other powders are said to produce better velocities. Hoping that equates to a flat shooting performance.
With the current carbon wrapped IBI barrels available to me I can only source 22” or 26”. 24/25 was about max preferred length for this project.

Any input welcome
I don't have a 280 AI but I have a 60s vintage BDL in 270. (not improved) I get 3000 fps with 150g Partition out of a 22" barrel and have for too many years to count. I use Remington brass, H4831 and CCI magnum rifle primers. No pressure signs, I do 10 reloads per case then throw them out. So 3000 fps should be easier to get with a 280 AI with a 150g bullet. All barrels are different though so be careful.
 

Ray B

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If the sharp shoulder had an appreciable effect on efficiency, that is, it caused velocity to increase for a given powder charge, one would expect cartridges where everything was equal to other cartridges except case shape to have more velocity. Comparing cartridges such as the 300H&H, Win Mag, Wby Mag and Ackley the potential velocities appear to be a function and proportionate to the case capacity. This would indicate that case shape may have only a small influence of potential velocity, if any.
 

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Well, I had a good idea , and it went to shit.

I thought what if I buy a .280 or 7X64mm and rechamber it

I did the research and it’s seems that 7X64mm an be rechambered To .280ai

Simple enough maybe the gunsmith can relieve the shoulder and re time it to headspace and rest amp the calibre.

New action with new factory barrel cheapest option for such a build.

I emailed a la asking if there are 7X64mm Tikka available preferred stainless fluted but request price and availability.

The response, sorry they seem to be discontinued. ahh, maybe it’s just discontinued by the importer but frustrating as it seemed like a cost effective option.
 

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