Originally Posted by
Rcmaveric
I use the BHN and pressure relationships to tune loads and play with new powders. It is more of a reference and no so much a hard set rule. I like to use it as means of establishing a starting point. Once you establish a safe starting points that should be reasonably accurate then you can go use the scientific method to tune your own optimal load.
I am similar to dwtim. I use a lot of range scraps. I mix and match to make general purpose alloys of 8, 10 and 12 BHN. Then i calculate min and max pressures. Then i use Quickloads to generate my shot tests that go below and over those pressures. Then i head to the range. The targets will let me know what the gun likes and what is happening to the lead. You will hit a point where the groups rapidly turn into a shot gun pattern. Why those hopefully looking groups degrade can be a any number of reasons besides over pressure though. I have found that the best accuracy is found close to those points of failure.
Now introduce gas checks into the equation and you just changed how much pressure you can put on the leads tail end. So that makes the BHN vs Pressure relationship less of a fact and more of reference for a starting point. There are a lot of things that can change the pressures inside in the chamber and changes the powders burn characteristic with out gaining any velocity.
So for new caster moving into more advanced fields like playing with new powders. I encourage the use of the BHN's for pressures. Like i said though it will to create a safe starting points to start your testing. Most often i find the best accuracy is close to those points of failures and the pressures are normally quite higher than first calculated. But i had to get the conclusion some how. I am also big on the "8 BHN general purpose pistol alloy, 10 BHN general purpose everything alloy, and 12 BHN general purpose rifle alloy" band wagon. There isn't nothing i haven't been able to get shooting good with those.
@Megasupermagnum, you are correct you don't need super hard bullets to get good accuracy. Fit is more important then hard alloys. We all ready know that bullet manufactures use hard lead and hard lubes to make their product survive shipping. Hard bullets are also a band aid fix for poor fitting bullets. I disagree with the concept being garbage though. I think it is great info for new casters. I think we just don't teach it good enough. The reason your 30-30 doesn't need that 26BHN bullets is because it is gas checked and the bullet fits good (i am assuming the fit is good) taking that 25k ish max psi alloy and making more like max 35-39k psi. The 30-30 is also a lower pressure riffle round (42k psi) and its easy to get higher velocities due to the lower pressures. The reason your accuracy is poor with those hard bullets is because they are too hard to obturate efficiently. So you just proved a portion of the theory about the min PSI. There are things that affect the max limit. The alloy content can also affect the leads performance under pressure and its max PSI. You will never know what your alloy can do until establish a test window safely and see what your lead does under those conditions.