30/30 AI is supposed to not have much back pressure. Least Mr. Ackley took the locking blocks out of a 30/30 and fired it with just the lever keeping the action closed. The reduced bolt thrust allows reloading to higher pressures. This is because the AI round has strait shoulders, and the case is not tapered.
Old PO was selling rivers of snake oil. None of his data is instrumented so his results are not repeatable. The idea of taking the lugs off a 30-30 AI to show there is case friction, well I could have told the world that. I discovered case friction decades ago when I had to get a cleaning rod to knock out a stuck case. I have repeated this experiment time and again, as loads developed in 70 F weather occasionally cause problems in 90 F weather.
What P.O Ackley did not do was fire a 30-06 AI and see if that case would stay put without a locking mechanism. I doubt it would, most certainly not the case case head. Around 24,000 psia the sidewalls will give way and the case head would pop out, assuming the front of the case stayed in the chamber. A 30-06 AI ought to operate around 60,000 psia. I have never heard Ackley supporters volunteer to fire their AI cartridges without locking lugs or a locking mechanism, maybe the ones that tried are now dead. I would like to find some Ackley fan boys who would do this and photograph them for the Darwin Awards. It would be funny to see one of them with a cartridge case sticking out of their forehead. Look Ma, no lugs!
P.O Ackley was claiming that his straight case design increased case to chamber friction, therefore it was OK to add lots of powder. His claim was that transferring the load to the case lessens the load on the bolt and therefore, increasing chamber pressures is just wonderful and A OK with AI cases. He never really proved that his case design reduced bolt thrust anymore than any other case, and he totally ignored the problem of where the load goes. In P.O Ackley's world, it just went into the dark universe. It does not, it goes somewhere, and that somewhere is the case and the barrel. He was increasing the stress on the brass case, which is a lot worse than increasing the stress on the bolt, because the bolt is steel. And he ignored barrel loads, though in one of his experiments he bulged the barrel of a Savage M99. He sort of ignored that too.
The only way P.O got the velocities he describes in his book was by creating insanely high pressure levels. There is not a forum for ruined and blown up Ackley Improved rifles, but tid bits about the carnage that P.O created lay about if you look:
http://thefiringline.com/forums/showpost.php?p=6265950&postcount=11
He pushed 150 and 170 grain projectiles so hard in that .30-30 AI Marlin 336, that he started having instant case head separations with factory loads.
He took it back to the gunsmith that did the rechamber, and the guy asked him if he had a death wish.
"What the [fleep] were you doing? You bent the locking lugs and stretched the action, you [dimwit]!!"
To this day, that gunsmith (whom I do business with) keeps two of the fired cases from that 336 on his work bench (one from testing after the rechamber; one from my grandfather's string of case head separations/failures). They're a reminder to him that he needs to get a better idea of the customer's expectations before taking on certain jobs.
You can increase the velocity of the bullet by increasing the amount of powder in the case. Savants on other forums give out a rule of thumb that a 40% increase in case volume provides a 10% velocity increase, implicit is the assumption that this is isobaric. This may be a crude rule of thumb, and I have done nothing to verify this. As stated by a previous poster, you might gain 60 fps, you might get less. What will happen is that your rifle will be hard to sell. I have seen this at gunshows and talked to the vendors. A regular rifle in a "Walmart caliber" will sell, but odd ball cartridges, such as Ackley Improved, they sit on the table through many shows, until they are almost given away.
If you want 308 Win velocities, buy a 308 Win.
