| DarylS |
| (.700 member) |
| 18/08/09 11:15 AM |
|
Re: Case taper, extraction... and the Martini Cadet
|
Quote:
I think the reason is simply that single shot actions, as opposed to bolt actions, have a certain amount of "give" in them, and when a tapered cartridge is fired, the action springs slightly, which allows the cartridge case to obturate to slightly more than the normal chamber size. Then, when the pressure subsides, the action snaps back, and the now oversize cartridge case is driven forward into the chamber, where it is tightly wedged and resists extraction. A straight sided case would not have the same wedging action and therefore extracts easily.
Exactly - bolt or block thrust with tapered cass - no such (or minimal) bolt/block thrust with straight cases.
I've had Ackley Imp chamberings that I stopped progression of loads due to working past where I thought the absolute max point should have been, not due to any pressure signs. When a .257 AckImp beats a .257 Weatherby magnum for speed with 100 and 120gr. bullets, it's time to back up a hundred fps or so and take a good look at the stats. There were absolutely no pressure signs by case measruement nor with no expansion of primer pockets, yet the chronographed results were there - same day/same time testing as well.