That's a valid point. The throat on this chamber is quite short, 100 grain bullets seated to touch the lands still extend quite a bit below the neck junction. This was the very first chamber cut by this Clymer reamer which would make one think it is on the maximum side of spec. I bought it specifically for this job and the probability of creating a few more .243 AI's in the future.
I'll save the before numbers and measure teh cases again on the second firing in the Ackley chamber to see if the average capacity increases.
Still not sure why I was getting almost 135 fps more (3135 fps) with book loads for the .243 and the Sierra 100 Spitzer, that being the 45 gr. of H4350. That same load gave 3096 fps with the 100 grain Hornady. The 100 grain bullets were seated right to touch the lands, that's the only difference I can see.
But getting away from all this ballistic gack and trying to show that 1% of anything is somehow meaningful, I think the .243 loads in manuals were a bit shy of what could be possible simply due to the wider pressure variations in a given string that the parent case shows. They had to keep the average pressure down to avoid the possibility of any one round exceeding the maximum peak pressure.
Since the Ackley shape tames this and makes it behave better (so I have read and shall hopefully prove for myself), I would feel very comfortable running 100 grainers in the 3100 fps range. Especially since this rifle has a 24" barrel - well, about 23.75" since it was set back.
If one had good pressure testing equipment and could work up loads in an individual rifle to reliably know pressures that figure could probably be exceeded as well.
But again, velocity increase was not my objective in this project. The goals were to tame that propensity for ballistic variation, to keep the throat from eroding so quickly, and to get the added benefit of any AI case to reduce or eliminate trimming.
When I get my .250 Savage AI back from the smith (the barrel is "on the lathe" as of yesterday), then I shall be happy to report capacity increases measured in pints of water and perhaps a few thousand feet per second velocity increases over the parent case.
