Correct pressure for BHN?

[andym79]

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 recently been trying to develop accurate loads without exceeding this pressure in the 6.5X55. I guess the 30-30, 38-40 and 45-70 are more forgiving, as I have been able to achieve 'good' loads (from 13,000 - 20,000 PSI) with these cartridges (I guess they were all made to shot lead).

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 overlooked RPM threshold (again 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; suggesting that in terms of pressure loads should start where I was stopping.

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 as I have been, I would need to push the projectile at 1900 fps, and using H4198 as I have been 2000fps, 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.

[AlaskanGuy]

Good for you... I too read that same article... And totally try to pratice this when shooting cast.... Pressure dictates the BHN... So lower pressures equal lower bhn.... You are not over thinking this in my opinion... Just dont over complicate it... It is just one of the things that a caster learns.....

Its time for one of our rocket scientists to chime in. Where are ya Larry Gibson... He he

[cbrick]

Andy, the 1422 times BHN is a guide, there is nothing set in stone about it. It is just one more thing to look at working up a load. If your not getting any leading your boolit fits your rifle properly AND there is no need to obturate the boolit, if the boolit fits properly there is no way for it to obturate cause it already fills the bore.

Your using a 16 BHN alloy in the 6.5X55, why do you think 1900-2000 fps is too fast in that rifle with H4227 or H4198? What velocity are you trying to stay at? Within the velocity range that your trying to stay in how is the accuracy? Have you tried the higher charges and did you have any success?

Rick

[243winxb]

Make the boolits has hard as possible. Diameter .001" larger than groove. Put a gas check on the base. Use the Hodgdon 60% rule using H4895 (21gr). Use an "M" die. Have fun. I dont own one.

[andym79]

Andy, the 1422 times BHN is a guide, there is nothing set in stone about it. It is just one more thing to look at working up a load. If your not getting any leading your boolit fits your rifle properly AND there is no need to obturate the boolit, if the boolit fits properly there is no way for it to obturate cause it already fills the bore.

Your using a 16 BHN alloy in the 6.5X55, why do you think 1900-2000 fps is too fast in that rifle with H4227 or H4198? Rick

Because of the fast twist rate of 1:7.8 in my Carl Gustav and the 180,000 RPM being too fast. I meant to say the spin is too fast not the velocity, I would be happy with 1800-2000 fps, please see my other post

http://castboolits.gunloads.com/showthread.php?224281-H4895-in-M96!

[MtGun44]

"Make the boolits as hard as possible . . . . "

Groan! Not that same old baloney, again.

Get real. I hope you were kidding.

Bill

[cbrick]

Make the boolits has hard as possible.

:groner:

Rick

[zuke]

Did you get any leading before you stopped?
What kinda lube are you using?

[missionary5155]

Good morning
Oh the fun of convincing a obstinate barrel it really can shoot a lead boolit.
Some years back someone wrote to the effect that they stayed with soft boolits until the need arose to make it harder. So I decided maybe they had something there. Ya know it worked so well that is my basic plan for every new barrel I am priveleged to load for. Granted I do try to use a little common knowledge as in 40-1 does have limitations how much base pressure and torque it can handle. But I have shot alot of 50-50 (WW-range scrap or pure) at velocitiy and base pressure that baffles my thinking. And sometimes something so simple as a cereal box base wad stuck on the boolit base changes a pattren into a nice group.
The boolit material, the powder speed build up pressure, the lube and even neck tension.... as part of that never ending list of variables to include all the items the barrel has inside there that affect our goal.... make this a good adventure.
Sometimes it is that barrel (maybe yours) that defies all reason refussing to shoot lead that makes the challenge we need to grow somemore in the quest of understanding lead boolits even a hair more.
But hey like MtGun44's signature states.. If it was easy everyone would do it.
Mike in Peru

[btroj]

Hard as possible? Why? This isn't good advice at all, just repeating the same old garbage.

Make em hard as needed. This might well be far softer than you think.

[lotech]

The BHN guide is a rough recommendation only. Factors such as bullet fit and bore condition will allow successful use of a softer bullet than guideline suggestions. I believe it was FOULING SHOT editor Glenn Latham who years ago suggested using the softest bullet that will shoot well (without leading, of course) at the desired velocity. Latham's exact words were better put and more descriptive than mine, but the message was that the softest bullet will generally be the most accurate.

[243winxb]

How do i make my "J" boolits softer so they obturate ? I think they are too hard. :kidding:

[mdi]

I cast bullets for my revolvers for 14 years before I discovered the "formula". So I got a hardness tester and mixed my brains out, but got no better results than I did with plain old wheel weight alloy and making sure the bullet fit the gun. I put the tester away and still use about ww hardness alloy, 10-14 BHN, and no problems with my bullets up to and including magnum velocities...

[243winxb]

This whole relationship centers around the elastic limit for the allowy you are using and what the elastic limit is. the elastic limit is the point at which stresses can occur to an object and it will return to it's relative shape. Once you have reached the deformation stage it no longer returns to relative shape. this is a very simplified version of this topic as it pertains to engineering mechanics of materials.

This is meant to be a guide and to keep you within safe/acceptable limits for pressure and alloy for your purposes. Obturated bullets do not mean that the shape has went through plastic deformation, just that it has expanded and stayed within the elastic limits of the alloy.

The formula does not take into account other factors that aide in reducing friction and thus combined forces on the cast slug. As stated above, one member is getting very good accuracy with soft (by most peoples standards) alloys in high velocity loads (for cast anyway).

Another factor not talked aobut is the pressure curve of the powder/cartridge combination. Does it spike quickly (fast pistol powder in rifle size case) or is it a gradual increase (full case of slower powder). Protection of the bullet base can also be a factor, we routinely do this by gas-checking, using lube wads, or fillers.

Internal ballistics is complex and then couple it to a bullet made of an unknown alloy and that spells FUN (Further Understanding Necessary) that is only had by actually shooting.

The use of this technique is explained pretty well in Lee's Modern reloading 2nd edition. http://castboolits.gunloads.com/showthread.php?3211-BHN-and-Pressure&p=35425#post35425 Photo from here, castboolits. The one on the left was loaded over 17 grains of Lil' Gun. The one on the right was loaded over 13 grains of Lil'Gun. The one in the middle is not fired.If you exceed Lees Maximum pressure you will get Plastic deformation. http://i338.photobucket.com/albums/n420/joe1944usa/Lee358-158-RF.jpg The nose of a rifle bullet may bend to one side on firing, if the alloy is too soft. http://www.photobucket.com/joe1944usa