Pressure .vs Velocity.

[USSR]

Got a new toy: Model 1886 lever action in 45-70. So, I'm going load my 405gr cast bullets relatively light, say 1300 - 1400fps. Pressure will be very low. My .357 Magnum loads are nearly that fast but pressure is high. So, do you think I should use the same alloy (2.5/2.5/95) or something softer due to the 45-70's low pressure? Thanks.

Don

[Bird]

Your current alloy will work fine. Just make sure the bullet is the right diameter.

[Don1357]

You haven't given enough information.

Ideal hardness is a function of pressure, not speed. If you pick just about any reloading book take a look at the different powders and their estimated speeds and pressures; you'll notice one may do 20k psi and 1,300FPS, while another powder will do 20k PSI and 1650FPS. The speed bit is meaningless, the pressure is what you need to take into account.

Heck look at high end pellet guns, pushing pellets at 1,650FPS with dead soft lead, zero lube, and zero leading. Why? Because they may go fast but without enough pressure to turn the lead into putty.

In case somebody wonders it is not the temperature of the hot gasses, for the same reason that you can swipe your fingers across a lit MAPP torch and not get burned; there is not enough time for enough heat transfer to take place.

[USSR]

You haven't given enough information.

I thought I nailed it perfectly. Two bullets traveling at 1300 - 1400fps, one with very low pressure as in the 45-70, and the other at very high pressure as in the .357 Magnum. FWIW, my first casting session was with the previously mentioned 2.5/2.5/95 alloy. I will do a 2nd casting session with an alloy with about half as much Sb. Thanks.

Don

[Don1357]

The problem is that for a host of reasons your weapon chamber will have a say in how much pressure a given load generates.

If you can estimate pressure you can guestimate the hardness level you need. Then you try powders and bump the amounts up and down until you hit the sweet spot regarding to accuracy. Then you play with the alloy to see if there are any gains to be had softening or hardening it.

For most of my plinking shooting I don't bother. This year I'm going to try some long distance shooting with my 45-70 so I'm going to have to do all this and more to see how much accuracy I can squeeze out of my gun. This is for open sights so sadly I'm sure I'll be able to get it to be more accurate that I can be :\