First, read MBC's essay on BHN and how CUP is used to determine a BHN that won't result in leading:
http://www.missouribullet.com/technical.php
Ok, now my questions.
1) In their example, they cite a .45acp round consisting of a 200gr LSWC over 5 grains of Bullseye, 900 fps at 20k CUP. I'm looking at several sources of reloading data, and 5 grains of Bullseye will push a 200gr LWSC somewhere south of 900 fps, at CUPs of around 15k.
I'm not trying to be a stickler here, but they use their numbers to arrive at a BHN that they claim will cause no leading. But, it looks to me like their data is significantly off, and if I plug what I believe to be more accurate numbers into MBC's formula, I'm getting BHNs of 12 or so. This is a big difference, as their website implies you use their BHN 18 LSWC for 5gr Bullseye. By MBC's own reasoning, this load should be producing a fair amount of leading.
2) MBC offers a ".357 Action!" round that's a BHN 18 158gr SWC, for "magnum velocities". A "magnum velocity" for a 158gr bullet out of a .357 magnum should be around 1300 fps. So I'm looking at reloading data and I'm seeing that, on average, that load should produce around 40k CUP. If I plug THAT number into MBC's formula, I get a requisite BHN of a whopping 32. How is it possible that MBC's BHN 18 bullet can be pushed to those velocities without causing significant leading, as according to their own explanation? Indeed, in a different thread, MBC has said that that bullet has been pushed as far as 1450fps without leading.
Now, I've read a lotta threads around here where folks are talking about their pet loads and whether they cause leading, and there seem to be a lotta cases where one guy says a load causes no leading, and another guy stopped using that load because it caused too much leading. So is this all a "your mileage may vary" thing? If so, that's fine, but where does that leave MBC's handy formula? Indeed, why pay attention to BHN at all if everyone is getting different results?
http://www.missouribullet.com/technical.php
Ok, now my questions.
1) In their example, they cite a .45acp round consisting of a 200gr LSWC over 5 grains of Bullseye, 900 fps at 20k CUP. I'm looking at several sources of reloading data, and 5 grains of Bullseye will push a 200gr LWSC somewhere south of 900 fps, at CUPs of around 15k.
I'm not trying to be a stickler here, but they use their numbers to arrive at a BHN that they claim will cause no leading. But, it looks to me like their data is significantly off, and if I plug what I believe to be more accurate numbers into MBC's formula, I'm getting BHNs of 12 or so. This is a big difference, as their website implies you use their BHN 18 LSWC for 5gr Bullseye. By MBC's own reasoning, this load should be producing a fair amount of leading.
2) MBC offers a ".357 Action!" round that's a BHN 18 158gr SWC, for "magnum velocities". A "magnum velocity" for a 158gr bullet out of a .357 magnum should be around 1300 fps. So I'm looking at reloading data and I'm seeing that, on average, that load should produce around 40k CUP. If I plug THAT number into MBC's formula, I get a requisite BHN of a whopping 32. How is it possible that MBC's BHN 18 bullet can be pushed to those velocities without causing significant leading, as according to their own explanation? Indeed, in a different thread, MBC has said that that bullet has been pushed as far as 1450fps without leading.
Now, I've read a lotta threads around here where folks are talking about their pet loads and whether they cause leading, and there seem to be a lotta cases where one guy says a load causes no leading, and another guy stopped using that load because it caused too much leading. So is this all a "your mileage may vary" thing? If so, that's fine, but where does that leave MBC's handy formula? Indeed, why pay attention to BHN at all if everyone is getting different results?