A copy and paste from the .243 sidebar on the main page:
.243 Ackley Improved–More Velocity, Less Case Stretch
by Bob Blaine, Sinclair International
Parker Ackley reluctantly developed the .243 Ackley Improved (“AIâ€). Ackley finally gave in to his customers’ requests to develop the .243 AI. He had always felt that the .243 Winchester was already an improved configuration, but he did say that the best thing to be gained by improving the .243 Winchester was to substantially reduce the case-stretching problems. The .243 Winchester parent case has always stretched brass, almost as bad as the Swift. Even though you get more velocity with the improved .243, I’ve also found that the improved version gives a bit more throat life than the parent case does.
The .243 AI delivers more velocity by virtue of enhanced case capacity–roughly five grains more H20 capacity than a standard .243 Winchester. The .243 AI has a water capacity of approximately 57 to 58 grains, compared to 52-53 grains for the standard .243 Winchester.
Fire-Forming
As always, fire-forming is done by one of two methods. Most of you will fire form the brass with loaded .243 Winchester. Ackley always said to use factory loads, or reload equivalent ammo to have a “snappy†load to form the case out properly. You never want to use a reduced load to form with, since you need the pressure to form properly. If your rifle is chambered properly, you should feel a slight amount of resistance as you close the bolt on a new piece of brass. If you do not get this “feelâ€, you may need to seat the bullets out to .010″ to .015″ into the lands to make sure that the base of the case stays in solid contact with the bolt face. The fire-forming method I have been using more lately employs medium burn-rate pistol powders and Cream of Wheat. I will start by loading about 10 grains of SR4756 or Unique into the case, and then I fill the case up to the body shoulder junction with Cream of Wheat. I will then take a large pinch of polyester filler, which can be found at any fabric supply store, or sewing department, such as at Wal-Mart. I will then take the pinch of polyester and load it into the case so that it fills up the shoulder area of the case effectively making sure that the filler is held securely over the powder for fire-forming. During the fire-forming, I like to dry brush with a nylon bore brush every 10 to 15 rounds. This removes any loose debris from filler that has accumulated. [Editors Note: Do NOT seat a bullet using this "Cream of Wheat" method. You can cap the case with a bit of wax to keep everything in place. However, Bob finds the wax is not necessary if the polyester filler is placed securely.]
Recommended Loads
I’m often asked, “what gunpowder do you recommend� I generally recommend medium-slow or slow burn-rate powders for the .243 Ackley. I have found, with my rifle, that H414 is pretty much my first choice for use in the .243 AI. H414 tends to give me great accuracy, with good velocity. Saying this, I have tried many other propellants and have found the following powders to be worth looking at for your needs: AA-2700, H414, H4350, VV N150, VV N550, VV N160, VV N560, RL19, H4831sc, and VV N165, to name a few of the powders that I have tested over the years.
Different Reamers, Different “Improvedsâ€
One thing that you need to watch for is what version of the .243 Improved that you have. This depends, for the most part, on whose reamer you will be using for the chambering of your barrel. It is easy to determine if your .243 Improved is the .243 Ackley Improved, or the .243 Winchester Improved. If you have the .243 Ackley Improved, the shoulder-body section will measure .460″ dia. at this point. If you have the .243 Winchester Improved, the shoulder-body section will measure .455″ diameter at this point. Both cartridges have the 40-degree shoulder. I have used both versions and found that you can use any data developed for either version interchangeably.
The .243 Ackley Improved is one of the best long range varmint rounds going, and can add some extra punch for your light big game rifle as well. One would be hard pressed to ignore a cartridge as versatile as the .243 Ackley Improved.
Matt’s Screamin’ Yellow Ackley–The Need for Speed
.243 AI Speed Demon
In a long-range varmint rifle, speed kills. Ultra-high velocities deliver flatter trajectories and more explosive hits. And that’s where the .243 Ackley really shines. While we don’t advocate “pushing the limits†with factory actions, Matt Bianchini has explored the upper limits of .243 Ackley performance with his Farley-actioned long-range rig, fitted with a 29″ Lilja 3-groove, 8-twist barrel. Using a stout load of Reloader 25, Matt’s “Screamin’ Yellow Ackley†has topped 3340 fps with Clinch River 106s. That is serious speed for heavy 6mm bullets. This shows a well-built .243 AI leaves Dashers and 6XCs in the dust when it comes to pure velocity.
