Oregon Trail Laser-Cast bullets, Brinell Hardness and leading in barrel?

[popper]

The formula flat doesn't work for pistol. I shot LC in 30-30 and get leading at any stiff load. I shot them in 308 and no leading, same load, diff rifle. My leading was caused by bad fit in 30-30. They are more like 18 BHN. I shoot pure to 18 BHN (MCB) 40 SW, full 231, 180gr with no leading, SA. Is your loading process resizing the CBs? You also may want to change the lube.

 

[Fatelvis]

If a cast .452" bullet will push through all of your throats with mild pressure, you're golden.

And thats the winning suggestion!
Clean your chambers well, then drop a bullet into each one of them. If they baaaarley fall through, or need a slight nudge to push them through, they are the proper size. Its a quick way to see what you have, and if all the chambers are the same.

 

[Fatelvis]

I think waaaay too much is put into the hardness of cast bullets. When using average hardness alloy ~12 BHN I believe the sizing is more important for accurate shooting without leading. I use WWs with a little 95/5 solder mixed in, and never had problems with bullets from 38 Spl light target loads, all the way up to 30-30 pushed to almost jacketed speeds.

 

[918v]

That PDF says a 22 BHN bullet obturates at 10,600 PSI. I find that hard to believe, and it goes against my experience.

I think they mean the bullet begins to change shape at that pressure. The problem lies in how big your chamber is. If the LC bullet only swells by .0001" at 11000 PSI, but the throat is .001" bigger, then there's gonna be blowby.

I experienced leading in my S&W 625 with LC bullets. I experience no leading with the same bullet cast out of 12 BHN alloy. In either case, the bullet fits the bore and the cylinder throat perfectly.

At the same time, LC bullets do not lead in my 1911s.

I think that blowby in the forcing cone (as when the base of the bullet clears the cylinder but the front driving band has not yet sealed the bore) and forcing cone constriction (due to an overtoghtened barrel) has contributes to leading as well.

The problem with cast bullets is they require a good understanding of internal ballistics which 99% of reloaders do not have.

 

[Walkalong]

I think they mean the bullet begins to change shape at that pressure.

Sounds reasonable, but misleading to reloaders.

A good fit in an auto is much more forgiving of BHN than a revolver. No doubt about it.

 

[918v]

Sounds reasonable, but misleading to reloaders.

Yup. The problem is with the definition of obturate. Obturate means to close or obstruct, not to just change dimensions. But it is incorrectly used to denote expansion which is only half the equation.