andym79
06-05-2014, 07:27 AM
Hi guys I didn't really get an answer to this one as a post in a thread, so I am posting it as a thread!
I have been doing a bit more reading. When I got into using cast bullets I bought both the Lyman manual and the Lee modern reloading.
When I read the later it seem to make sense, a cast bullet can only take so much before it gets hammered! I refer to Richard Lee piece on pressure a BHN; the table lists maximum pressures recommended. For the particular alloy I use with a BHN of 16 the recommended maximum pressure of 20433 psi.
Following this advice I have been trying to develop accurate loads without exceeding this pressure.
Anyway giving the problem I have been having with the 6.5, I have return to 'cast boolit' school and tried to expand my understanding. Firstly thanks to Larry for pointing out the RPM threshold (my other rifles have more forgiving twists) secondly and I hope this is right, thanks to http://www.lasc.us .
So the question I am alluding to is this after reading through their website, it is clear that there is some contradictory evidence out there.
"Bullet BHN / "Minimum" Chamber Pressure For Lead Alloys (PSI)
If the bullet is too hard to obturate, gas cutting usually occurs on the base band on the non-driving side of the rifling and barrel leading is likely. Simply multiply the alloy BHN by 1,422".
So for my alloy 1422 X 16 = 22752 PSI. Hello this is in complete contrast to my interpretation of LEEs work; suggesting that in terms of pressure loads should start where I was stopping.
Does Lees work apply only to plain base bullets and not GC ones?
Can someone confirm for me if this is correct? If so in my 6.5 X 55 I should be aiming for a 1400-1500 fps load that develops a peak pressure of between 23,000 and 35,000 psi, correct?
I know some of you guys have suggested loads of fast powders that would get me there!
So am I right in thinking that I probably need to either move to a softer alloy 9-10 BHN or use a faster powder e.g Unique or Red Dot to achieve my goal.
Using Quickload (I know I can't take it as gospel) in order to get up to that PSI using H4227, I would need to push the projectile at 1900 fps, which is too fast!
Is this a moment of minor revelation or am I just confusing myself!
I suspect that this is just one of many factors, and the is no definite rule relating to PSI and BHN predict accuracy.
I have been doing a bit more reading. When I got into using cast bullets I bought both the Lyman manual and the Lee modern reloading.
When I read the later it seem to make sense, a cast bullet can only take so much before it gets hammered! I refer to Richard Lee piece on pressure a BHN; the table lists maximum pressures recommended. For the particular alloy I use with a BHN of 16 the recommended maximum pressure of 20433 psi.
Following this advice I have been trying to develop accurate loads without exceeding this pressure.
Anyway giving the problem I have been having with the 6.5, I have return to 'cast boolit' school and tried to expand my understanding. Firstly thanks to Larry for pointing out the RPM threshold (my other rifles have more forgiving twists) secondly and I hope this is right, thanks to http://www.lasc.us .
So the question I am alluding to is this after reading through their website, it is clear that there is some contradictory evidence out there.
"Bullet BHN / "Minimum" Chamber Pressure For Lead Alloys (PSI)
If the bullet is too hard to obturate, gas cutting usually occurs on the base band on the non-driving side of the rifling and barrel leading is likely. Simply multiply the alloy BHN by 1,422".
So for my alloy 1422 X 16 = 22752 PSI. Hello this is in complete contrast to my interpretation of LEEs work; suggesting that in terms of pressure loads should start where I was stopping.
Does Lees work apply only to plain base bullets and not GC ones?
Can someone confirm for me if this is correct? If so in my 6.5 X 55 I should be aiming for a 1400-1500 fps load that develops a peak pressure of between 23,000 and 35,000 psi, correct?
I know some of you guys have suggested loads of fast powders that would get me there!
So am I right in thinking that I probably need to either move to a softer alloy 9-10 BHN or use a faster powder e.g Unique or Red Dot to achieve my goal.
Using Quickload (I know I can't take it as gospel) in order to get up to that PSI using H4227, I would need to push the projectile at 1900 fps, which is too fast!
Is this a moment of minor revelation or am I just confusing myself!
I suspect that this is just one of many factors, and the is no definite rule relating to PSI and BHN predict accuracy.