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Several of the folks on this forum have asked about data for the Ackley Improved calibers. I will try to post some of the data today if the form transfers well, there will be more later. There is a lot of data here for several calibers, this will just be a sample for each of the calibers inquired about. First I want to say a word or two about the Ackley chambering in general.
Parker Ackley was a lot like me. A tinkerer and an experimentor, but much unlike me, he was a gunsmith. He chambered his own rifles and rebarreled rifles. Like many smiths he specialized in certain avenues of his trade. He worked at a time when few people could afford to buy another rifle to hunt a different species and there were very few shops were a person could swap one rifle for another. But more importantly, there were virtually no high velocity "Magnum" caliber available to the common working man. What he set out to do was to "improve" the performance of the various calibers available to us by increasing the powder capacity of the case to add velocity to it's performance.
One aspect of the Ackley chamberings was that all AI chambered rifles would retain the safe capability to fire factory rounds. That means that all his rechamberings allowed both factory rounds and improved rounds to be fired with the same headspace dimension. In my opinion, if this is lost, due to improper chambering or any other reason, then it is not an Ackley Improved chamber. Of course any round fired in the chamber of an AI rifle will then retain the case dimensions of the AI round. This is all there is to fireforming to Ackley improved dimensions. Now, I must say I have seen a lot of AI chambered rifles. Rifles that were marked as "Ackley Improved". Most of these that were older rifles, were smithed many years or decades ago, were made to the AI specification. Some were not. Most of the later made rifles were not to the Ackley specs. All of the rifles in which this AI data were developed were chambered to provide correct parent case headspace with both the AI case and standard factory case dimensions. Also, there is no AI "standard" dimension. His chamberings were never submitted to SAAMI or any other "standards" laboratory. Therefore, even if a rifle is marked as "Ackley Improved", there is no guarantee that the rifle will safely fire standard ammo or even AI ammo. If you own such a rifle and cannot determine if it is a true AI or not don't shoot it until you know what the chamber dimensions are.
Some of his improved cases offered significant increases in velocity, some did not. Those calibers which had a lot of taper in the original case will gain more room for powder than those that were nearly straight to begin with, such as the 250 Savage with it's pronounced taper compared to the almost straight 284 Win. There will be no discussion as to whether this "rechambering" is worth the effort or the expense. No matter what the results it's still much better than playing golf.
In general the AI case has less body taper and all have a 40 degree shoulder. As stated all retain the parent case headspace dimension. I mean all that headspace on the shoulder, obviously if a case is rimmed, such as the 30-30 or the 303 , that diminsion is retained also. Another point, there were several AI cases based on the 30-06 case. Calibers such as the 30-06 AI, the 338-06 AI, the 6.5-06 AI, the 35 Whelen AI, etc. Not all of these cases have the same improved shoulder diameter dimension. I don't know the reason for that but the drawings I have seen show this and the drawings in posession of the die manufacturers reflect this as well.
And, one more point. Ackley modified many cases. But only those cases that were available to him were included. Many cases which came about after he passed on were AI modified to the Ackley dimension, 40 degree, minimum taper, etc. are called AI cartridges, even though he never saw them.
Ackley was also, or became as his experiments went on, a proponent of high velocity. His theory was that a lighter weight high velocity round was a better killer of game than a large slow bullet. He was not alone in this belief, obviously, due to the increasing number of factory rounds available in high speed calibers. His work with the Army Ordinance department led to the development of the 5.56mm military round. He used to do his testing on San Clemente goats on the islands off the California coast. I did a little playing there myself a few years later.
All of these loads were safe in my rifles. They may not be safe in your rifles. You must follow safe handloading practices and procedures.
I fired several loads that were in excess of factory SAAMI pressure standards in my rifles. I used strong, modern bolt action rifles for all this development. Those loads which exhibited excess pressure are not included here.
Rifle: Sako AV Barrel Length: 24”
Caliber: 6.5-06 AI Case: Win 25-06 Primer:CCI-200
Powder:RL-22 Bullet: Sierra 140 grain spitzer COAL: 3.230”
Charge wt: Velocity: SD: Group:
56.0 grains 2978 fps 13 fps .8"
57.0 grains 3033 fps 15 fps .8"
58.0 grains 3078 fps 09 fps .5"
Powder:RL-25 Bullet: Sierra 140 grain spitzer COAL: 3.230”
Charge wt: Velocity: SD: Group:
59.0 grains 2996 fps 13 fps 1.0"
60.0 grains 3042 fps 11 fps 1.0"
61.0 grains 3081 fps 08 fps 1.0"
Powder:RL-22 Bullet: Norma 156 grain Vulcan COAL: 3.175”
Charge wt: Velocity: SD: Group:
55.0 grains 2822 fps 10 fps .6"
56.0 grains 2878 fps 06 fps .6"
57.0 grains 2907 fps 07 fps .3"
Parker Ackley was a lot like me. A tinkerer and an experimentor, but much unlike me, he was a gunsmith. He chambered his own rifles and rebarreled rifles. Like many smiths he specialized in certain avenues of his trade. He worked at a time when few people could afford to buy another rifle to hunt a different species and there were very few shops were a person could swap one rifle for another. But more importantly, there were virtually no high velocity "Magnum" caliber available to the common working man. What he set out to do was to "improve" the performance of the various calibers available to us by increasing the powder capacity of the case to add velocity to it's performance.
One aspect of the Ackley chamberings was that all AI chambered rifles would retain the safe capability to fire factory rounds. That means that all his rechamberings allowed both factory rounds and improved rounds to be fired with the same headspace dimension. In my opinion, if this is lost, due to improper chambering or any other reason, then it is not an Ackley Improved chamber. Of course any round fired in the chamber of an AI rifle will then retain the case dimensions of the AI round. This is all there is to fireforming to Ackley improved dimensions. Now, I must say I have seen a lot of AI chambered rifles. Rifles that were marked as "Ackley Improved". Most of these that were older rifles, were smithed many years or decades ago, were made to the AI specification. Some were not. Most of the later made rifles were not to the Ackley specs. All of the rifles in which this AI data were developed were chambered to provide correct parent case headspace with both the AI case and standard factory case dimensions. Also, there is no AI "standard" dimension. His chamberings were never submitted to SAAMI or any other "standards" laboratory. Therefore, even if a rifle is marked as "Ackley Improved", there is no guarantee that the rifle will safely fire standard ammo or even AI ammo. If you own such a rifle and cannot determine if it is a true AI or not don't shoot it until you know what the chamber dimensions are.
Some of his improved cases offered significant increases in velocity, some did not. Those calibers which had a lot of taper in the original case will gain more room for powder than those that were nearly straight to begin with, such as the 250 Savage with it's pronounced taper compared to the almost straight 284 Win. There will be no discussion as to whether this "rechambering" is worth the effort or the expense. No matter what the results it's still much better than playing golf.
In general the AI case has less body taper and all have a 40 degree shoulder. As stated all retain the parent case headspace dimension. I mean all that headspace on the shoulder, obviously if a case is rimmed, such as the 30-30 or the 303 , that diminsion is retained also. Another point, there were several AI cases based on the 30-06 case. Calibers such as the 30-06 AI, the 338-06 AI, the 6.5-06 AI, the 35 Whelen AI, etc. Not all of these cases have the same improved shoulder diameter dimension. I don't know the reason for that but the drawings I have seen show this and the drawings in posession of the die manufacturers reflect this as well.
And, one more point. Ackley modified many cases. But only those cases that were available to him were included. Many cases which came about after he passed on were AI modified to the Ackley dimension, 40 degree, minimum taper, etc. are called AI cartridges, even though he never saw them.
Ackley was also, or became as his experiments went on, a proponent of high velocity. His theory was that a lighter weight high velocity round was a better killer of game than a large slow bullet. He was not alone in this belief, obviously, due to the increasing number of factory rounds available in high speed calibers. His work with the Army Ordinance department led to the development of the 5.56mm military round. He used to do his testing on San Clemente goats on the islands off the California coast. I did a little playing there myself a few years later.
All of these loads were safe in my rifles. They may not be safe in your rifles. You must follow safe handloading practices and procedures.
I fired several loads that were in excess of factory SAAMI pressure standards in my rifles. I used strong, modern bolt action rifles for all this development. Those loads which exhibited excess pressure are not included here.
Rifle: Sako AV Barrel Length: 24”
Caliber: 6.5-06 AI Case: Win 25-06 Primer:CCI-200
Powder:RL-22 Bullet: Sierra 140 grain spitzer COAL: 3.230”
Charge wt: Velocity: SD: Group:
56.0 grains 2978 fps 13 fps .8"
57.0 grains 3033 fps 15 fps .8"
58.0 grains 3078 fps 09 fps .5"
Powder:RL-25 Bullet: Sierra 140 grain spitzer COAL: 3.230”
Charge wt: Velocity: SD: Group:
59.0 grains 2996 fps 13 fps 1.0"
60.0 grains 3042 fps 11 fps 1.0"
61.0 grains 3081 fps 08 fps 1.0"
Powder:RL-22 Bullet: Norma 156 grain Vulcan COAL: 3.175”
Charge wt: Velocity: SD: Group:
55.0 grains 2822 fps 10 fps .6"
56.0 grains 2878 fps 06 fps .6"
57.0 grains 2907 fps 07 fps .3"
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