This is what AG has to say about it, it's apparently not real popular, they have no loads submitted for it. Being a wildcat they have no pressure spec, but it would be in the neighborhood of the parent cartridge family.
Nominal performance 100gr bullet @ 3000fps
Based on the .30-06 Springfield necked down to .243 inches, this wildcat was popular at one time. However, the increase in case capacity over rounds such as the 6mm Ackley Improved provides a negligible performance increase due to the overbore characteristics inherent in large case volumes and small bullet diameters.
The inability to propel 6mm bullets much faster than the standard 6mm-06 may be why wildcatters did not hold much preference for the the 6mm-06 Ackley Improved over this round.
However, the 6mm-06 has no ballistic advantage over the 6mm-284 and, both having .470" rims, the shorter length of the latter lends itself to shorter actions and a lighter rifle. Accordingly, the 6mm-284 is probably a better choice for building a modern high prformance 6mm varmint or target rifle. 6mm Rem Ackley Improved...
Nominal performance 90gr bullet @ 3300fps
Ackley realized that the factory .244/6mm Remington case provided close to the maximum powder capacity one could efficiently use with a .243 bore. Comparing his "Improved" designs with the factory round, he stated "only a modest increase in velocity is possible" and even then with considerable additional powder consumed.
Ackley's load data pushes a 90 grain bullet at a maximum muzzle velocity of 3452 fps. 6mm-284...
Nominal performance 100gr bullet @ 3207fps
The 6mm-284 will push all bullet weights about 100 to 150 fps faster than is possible with the 6mm Remington. Ballistically, the 6mm-284 and the .240 Weatherby Magnum are very similar
Due to its extremely sharp shoulder angle, the .284 Winchester case is subject to collapsing when its neck is squeezed down to a smaller caliber, resulting in a high percentage of ruined cases.
http://www.chuckhawks.com/6mm-06.htmFWIW, I went with the 6mm Rem Ackly Improved on my t-hole Ultra and a CVA OE, haven't shot them yet tho.
http://www.6mmbr.com/gunweek042.htmlComparing the 6mm Rem AI with the .243 chamberings, I think the 6mm Rem AI comes out on top. The 6mm AI is ALL the cartridge any varmint hunter needs. It will do anything you want to do with varmints, any kind of varmint. And in a 10-twist, it is the best 1000-yd varmint caliber you can get your hands on period. The long-necked 6mm AI will have less throat erosion than the short-necked .243 or .243 AI. The 6mm Rem AI will also hold a little more powder than a .243 Ackley. For long-range varminting, sending light bullets at ultra-high velocities, I just think the 6mm Rem has better case design than a .243 Win. With either case, definitely go with the Ackley version. The 40° shoulder gives you a little more powder capacity and both the shoulder angle and the reduced body taper give you better brass life. A case with no taper won't stretch as much as a tapered case." Tim
