alloy vs bhn vs psi/cup

[ubetcha]

I have a question that I can seem to find an answer for. For instance, I have a 7.7mm Arisaka with a .313 bbl. How can I find out what kind of pressure I will generate with a particulur powder charge like 13gr Red Dot. Now translate the pressure into alloy BHN needed to successfully "bump up" the bullet (Lyman 314299 or Lee 312185) to seal the bore. Using a alloy calculator and the Lee Bhn to pressure chart,I need to figure out what pressures I'm getting. I hope this make sense of what i'm trying to explain. Thanks

[Sasquatch-1]

I am not sure what you are asking. Are you asking how hard of a bullet you need to prevent leading at a particular pressure?

[btroj]

Take that chart and use it for flux. Best thing to do with it.

The chart doesn't tell you squat. A BHn much lower or higher than "ideal" may work wonderfully.

Good fit, a good lube, and a proper powder choice will do wonders in giving good accuracy with cast.

[ubetcha]

I guess what I'm trying to say is,I will use the 314299 unsized if it's over .313 using an alloy of 4lbs ww to 1lb lino.The calculated BHN is about 13. Will this be hard enough or to soft for the use of 13gr RD. The Lee 312185 cast at .313 using ww's unsized.I have not measured this one with the 4-1 alloy yet.I guess I will have to load the up and see if I have any leading at any volicities.I plan on keeping it at between1500-1800 fps.There are other powder I have that I will try also. Just want to start with RD right now. At our IHMSA silhouette matches ,we also conduct cast bullet rifle too. Same distances and targets. 200m the farthest target

[uscra112]

From somewhere I have a rule of thumb on a spreadsheet that says BHN x 1500 = Optimum psi.

Quickload will give you a pretty good idea of pressure for a given load. A very rough model for the 7.7 Arisaka and 314299 at 200 grains with 13 grains Red Dot gives 37000 psi, which is right up there as far as the SAAMI pressure rating goes. I'd be happier with a slower powder like Blue Dot. The high pressure (and rate of rise) of the Red Dot load may well give you nose slumping with a 13 BHN boolit. AA#9, 2400, 4100, 1680, 4198, or my favorite AA5744 will treat the boolit better.

[Frozone]

From somewhere I have a rule of thumb on a spreadsheet that says BHN x 1500 = Optimum psi.

That number should be about right, BHN X 1440 is often given as the obduration pressure for an alloy.
So 1500 should be just high enough to ensure it, without being so high as to cause problems.

Somebody mentioned the LEE chart - I always looked at it as 'backwards'. The 'max' is were the alloy Starts to obdurate.

[btroj]

4 pounds ww to 1 pound Lino will work in any gun. With any sane load. Water drop those and they will be way beyond 13 BHn. Way beyond.

I often shoot far softer bullets than should work. I don't tell my guns and they don't seem to care.

I don't have the Lee book. I understand the concept but is that the ideal BHn, the low, the high? What exactly does that number tell us? It isn't knowing the number, it is how useful is that number in helping us determine a good load with that alloy.

[Defcon-One]

I'd use Lyman #2 alloy, with gas checks. Never had a problem with that combo.

All the worrying and chart searching is a waste of time. Cast a small batch, load them, shoot them and see.

Change powders if you can't get what you want from that one safely. If it works, it works. If not, you will know!

In my experience the charts and "science" are often wrong. They are only guidelines to get you close for final testing!

[Freightman]

spend time shooting rather than calculating shooting is far more fun calculating makes my head hurt. :kidding:

[ubetcha]

4 pounds ww to 1 pound Lino will work in any gun. With any sane load. Water drop those and they will be way beyond 13 BHn. Way beyond.

I often shoot far softer bullets than should work. I don't tell my guns and they don't seem to care.

I don't have the Lee book. I understand the concept but is that the ideal BHn, the low, the high? What exactly does that number tell us? It isn't knowing the number, it is how useful is that number in helping us determine a good load with that alloy.

That's kind of what I was working with as what the number mean.I know the charts not carved in stone so to say. It's somewhat of a referance which can be confusing and send one in the wrong direction. Just wondering what others have had success with as to what alloy they are working with.

[btroj]

I would use 50-50 ww and lead and water drop them. Ww/Lino will e plenty hard.

In the end it echoes a case of learning thru experience. Try different mixes and see what happens. Does it lead? Does it shoot better? What is available to you?

Many factors other than BHn matter. I use lots of range scrap because I have lots of it. If I had lots of ww I would use them.

Don't be afraid to experiment. Lead is easy to remove from a barrel. Bad groups are a learning experience.