Re: 7mm Mauser resizing issue
Posted: 31 May 2017 17:06
I take a deep breath .
There are several physics things happening that I lack the book learning to describe but bear with the wrench bender .......
Several points 1 is that if these were the first cast down the bore and or it was a clean bore then what you are seeing is the bullet raising pressures in the first inches of the bbl as the lead and lube , and I hate the word , season the bore . Think of it like the first time you used olive oil in your bacon grease cast iron pan ...... It's not the same but similar .
As the bullet lube gets uniform in the bore the high spikes go away because the bullet is riding on slickum' from the last shot while it adds some to replace what it squeegees off .
That sort of explains why the lessor loads did that . It's possible that the load was in a ragged edge of explosion vs burn . There are a bunch of big words but what really happens is that you have a space volume and a pressure curve that allows too much of the powder to burn before the bullet moves . Basically the powder is at peak pressure and maximum expansion inside the case instead of 2" up the bbl . Unique is fairly forgiving in this respect .
For a mental image think about the last time you kicked a solid frame panaled inside door open . That's what the charge is doing the whole thing springs then swings open .
In your 2nd load you have a 500 fps swing , not good for consistency . 1700-2200 fps . Look how your 8-9 gr loads settled down . If you reshoot the 7 gr loads I'd bet on seeing them in the middle 1200s now . I'd bet on you finding a sweet spot seated long somewhere about 8.7-9.5 if you don't get leading .
There are several physics things happening that I lack the book learning to describe but bear with the wrench bender .......
Several points 1 is that if these were the first cast down the bore and or it was a clean bore then what you are seeing is the bullet raising pressures in the first inches of the bbl as the lead and lube , and I hate the word , season the bore . Think of it like the first time you used olive oil in your bacon grease cast iron pan ...... It's not the same but similar .
As the bullet lube gets uniform in the bore the high spikes go away because the bullet is riding on slickum' from the last shot while it adds some to replace what it squeegees off .
That sort of explains why the lessor loads did that . It's possible that the load was in a ragged edge of explosion vs burn . There are a bunch of big words but what really happens is that you have a space volume and a pressure curve that allows too much of the powder to burn before the bullet moves . Basically the powder is at peak pressure and maximum expansion inside the case instead of 2" up the bbl . Unique is fairly forgiving in this respect .
For a mental image think about the last time you kicked a solid frame panaled inside door open . That's what the charge is doing the whole thing springs then swings open .
In your 2nd load you have a 500 fps swing , not good for consistency . 1700-2200 fps . Look how your 8-9 gr loads settled down . If you reshoot the 7 gr loads I'd bet on seeing them in the middle 1200s now . I'd bet on you finding a sweet spot seated long somewhere about 8.7-9.5 if you don't get leading .
