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#16
02-23-2005, 07:08 PM
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Nope, I'm not talking about those occasional extreme pressure events, such as happen with very reduced charges of very slow powder.
I was referring to the high point of the pressure curve, which I perhaps should have called peak pressure instead of "spike". That peak can occur before the bullet even clears the case neck, and that's what "hammers" the base of the bullet, causing what you might call over-obturation. All the obturation occurs while the bullet is in the leade or freebore area, and then it is almost immediately swaged back down by the bore and rifling. Indeed, the rear of the bullet can be still expanding while the front part is being swaged down, depending on the exact geometry of the throat/leade. Once it's fully in the rifled part of the barrel, it cannot expand any more, obviously. Interesting stuff, huh?
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#17
02-23-2005, 10:26 PM
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I should have added that the barrels are new,and the longer throated.There is no 243 throat erosion.On the 264 ,Bill did a longer throat to avoid the spikeyness of a short throated 264.With IMR 7828 it takes 2 more grains over book max to reach max velocity of 3100.That was also the only acceptable group,1",I got with IMR7828.I have been told IMR7828 has a narrow window.
The book max for N-560 with 140 is 2990,I'm at 3045,and again.????Understand the book max is CIP not SAAMI,the Europeans have no use for the 264 chambering,they limit it to about 56,000psi.My primers still have half the radius.But then again,I don't have any thing really to compare Gevelot pockets to,the other two magnums use Winchester and Norma.The primers are the soft shelled CCI 250.My lot of N-560 is slower than my buddies RL-22,in my 338WM anyway.The last loading gave a 1/2"group.That's more like what I have come to I expect with N-560. Bullet do expand,sometimes with very sad results,but these are not Partions, but the slippery boat tailed SSTs.Barrel friction in 264,was the reason I had it rebarreled,the FN barrel had too much lands. When it' happened,my first thought was that I had broke in the barrel.It's a 24" Douglas. A 264, if it's nor accurate and fast is not worth the effort. Last edited by Downwindtracker2; 02-23-2005 at 10:33 PM.
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