Rambling Thoughts on Ackley Improved Cartridges
by Greg Ritchie
My introduction to improved cartridges was by way of the 22/250 Ackley Improved. A friend had his 22/250 rechambered thus and was trying for the magical 4000 feet per second mark. I remember the first shot I fired out of the rifle with some forgotten 52 grain bullet. The bullet never made it to the target, instead the velocity and rotational forces caused the bullet to disintegrate shortly after leaving the muzzle. Today I understand that this was the wrong bullet for the application, but my young mind was impressed at such a powerful cartridge and thus my fascination with improved cartridges began.
P. O. Ackley is the name most often thought of when improved cartridges are mentioned. He was a well known gunsmith and writer in the 1960's. His idea on improved cartridges was to minimize body taper and sharpen the shoulder to 40°. This resulted in a cartridge that gave quite a velocity boost to the parent cartridge, sometimes as much as 10% or more!
There are other advantages to improved cartridges also. Case stretching is greatly reduced, as is back thrust. It can also eliminate headspacing issues, especially with rimmed cartridges. Another advantage is more efficient combustion of powder. The theory is that the sharper case shoulder causes combustion to take place inside the cartridge case, rather than in the leade and first few inches of barrel. Yet another advantage is that standard factory ammunition can safely be fired in improved chambers. Forget your ammo for the 30/30 AI? Not a problem, just run down to the local hardware store and pick up a box of standard 30/30.
Of course there are disadvantages also. That 30/30 AI I mentioned? It might not work as well in your lever gun as do the standard rounds. The sharp shoulder and straight case can cause feeding problems. A problem that could be remedied by tuning the rifle.
Let's look at a couple of the improved cartridges I have owned and one that I am thinking about.
First, the 22 Hornet. I was thoroughly disappointed in my first 22 Hornet. It shot patterns, not groups. Not wanting to give up on it I started to handload for it. Groups instantly tightened up. But then I ran into a second problem. Cases were not lasting long, sometimes showing signs of incipient case head separation after just one or two firings. The cases had to be trimmed after every firing. The cases are an old design and thin, but they should last longer than this. What to do? Headspace off the cartridge neck was the first thought, but nearly impossible to do with the Hornets long sloping neck.
The answer was to have the rifle reamed to K-Hornet. Designed by Lyle Kilburn who blew out the case and sharpened the shoulder. The K-Hornet was also supposedly able to push the 45 grain bullet to 3000 feet per second, a claim I could not reproduce. I simply took factory Hornet ammunition, fired it through the K-Hornet chamber and viola. K-Hornet brass. Nearly every every case survived the transition. I loaded the 45 grain pill to just over 2750 feet per second. Case life was greatly increased, requiring trimming after about 4 firings and getting about 8 or 10 firings out of each case before discarding them.
Second was the 30/30 Winchester. I liked what happened with the 22 Hornet so well, I thought I would apply the same set of goat glands to my 30/30. Same model rifle, just a different chambering, to see what happened. I had this one chambered to the Ackley Improved version. The 30/30 AI straightens the case, adds a 40° shoulder and lengthens the case body by blowing out the neck. Ackley claimed 2700 feet per second with this one.
I did lose a few cases when firing factory rounds through the 30/30 AI chamber. The cases I lost failed where the neck was blown out to form the new shoulder. About 2 cases in every 20 round box would crack in this area. The remaining cases lasted a long time though, 15 or more firings. They would go as many as 10 firings without needing to be trimmed. Again, I could not get 2700 feet per second but I could get nearly 2600 fps. I settled on a load that pushed the 150 grain bullet at 2550 fps.
So what did I achieve with the Improved cartridges? Accuracy was the same both before and after the rechamberings, no better and no worse. The 22 Hornet benefited greatly from handloading. I did see an increase in velocity, but the biggest advantage to my minds eye was the great increase in case life.
Which brings me to my current delima. Do I want to rechamber my 280 to Ackley Improved? A quick look at published reloading data shows the 280 can launch a 140 grain bullet at 3000 fps, the 280 AI will launch the same bullet to 3200 fps. The 7mm Remington Mag will launch the same 140 grain bullet to 3200 fps. The same can be said of the 160 grain bullet, but the figures are 2800, 3000, and 3000 fps. So I can get the same performance as the magnum offering, but with less bolt thrust and less powder.
To sum it up, improved cartridges are an economical way to increase velocity, and case life. The conversion is inexpensive as well, the rechambering can be done for around $100. $50 or less if you can do the work yourself. Cases are easily formed from the factory parent case. Less powder is used to achieve the same velocity as would be accomplished by using the next larger cartridge. Reloading dies are easily acquired, Lee Precision, known for value, catalogues AI dies in 22/250, 223 (interesting), 30/30, and 280. And you would have your own unique rifle. What's not to like!