I've been reloading for several years and have realized that I tend to use powder and data that is printed for the bullets that I happen to have. My question is: is there any real difference (that is, harmful difference) in using reloading data written for lead bullets or jacketed bullets or SWC or hollow points etc. as long as the bullet weights are the same? And as long as I'm asking, if I used data for 158 gr. bullets what effect could I expect using the same data with 124 gr. or 220 gr. bullets?

It will take more effort (energy) to cause the jacketed bullet to engrave the rifling and be propelled down the bore, moreso than a cast bullet that is .001" overbore size.

You can use jacketed bullet info for cast bullets safely, but not vice-versa. Also, at higher velocities, you'll get more leading from the cast.

Don't try to interpolate loading info from one bullet weight load to another bullet weight. Always stick with the manual's recommended load limitations.

As I have written many, many times, it is the bullet that creates the largest differences in pressure from load to load. Even when bullets are the same weight, they will have different jacket thickness, different jacket alloys, different ogive, different bearing length, different core hardness, different diameter, etc.

It might not matter if we were simply throwing bullets,. Weight would be the only consideration in that event. But we aren't. We are in essence extruding the things down a bore slightly smaller than the bullet is, under 50,000+ psi. Think of it that way and you realize there's a whole lot going on in there, and almost all of it changes when the bullet does.

As I have written many, many times, it is the bullet that creates the largest differences in pressure from load to load. Even when bullets are the same weight, they will have different jacket thickness, different jacket alloys, different ogive, different bearing length, different core hardness, different diameter, etc.

It might not matter if we were simply throwing bullets,. Weight would be the only consideration in that event. But we aren't. We are in essence extruding the things down a bore slightly smaller than the bullet is, under 50,000+ psi. Think of it that way and you realize there's a whole lot going on in there, and almost all of it changes when the bullet does.

Well worded, Rocky...and 100% true.

Seldom to two differnt bullets of the same weight have the same bearing area...which can change seating depth, case volum as well as increasing friction brom the increased barrel contact. Jacket material is not only harder, it doesn't have those lube grooves that reduce the effort of engravment....and all jackets aren't made of the same alloy or made to the same thickness.

Have to also consider what happens as the bullet changes with the application of intense pressure to the base.

I'm convienced that at the very uppper levels, lead bullets can produce more pressure than jacketed....once pushed past the point of the alloy's ultimate strength, lead seem to become more like an obstruction than a projectile. Given a very soft bullet...kick it in the rear with a load that produces 50K pressure with a jacketed bullet load and i expect you'd go way-way past the 50K range.

It's been my finding that loading for the same weight bullet jacketed or cast, using a .357 for an example, that it takes less powder to get a cast bullet to go the same velocity as a jacketed bullet.

Using 2400 for example it takes 3-4 grains less to get the same velocity from a 358156 158 grain gas checked bullet as it would a 158 grain jacketed bullet. Even bullets from different manufacturers will have different velocities with the same bullet weight and powder charge. Why? Like Rocky said, ojive, bearing surface, jacket metallurgy maybe?

But that's why we reload so we can tinker with all the little quirks that go with it. Sometimes frustratingly but none the less we learn something from the proccess. But always safely. :D

RJ

It's also my theory that jacketed bullets cause rapid pressure jumps at top end, too. Have you ever seen or heard about velocity actually decreasing when powder charges pass a certain amount? (This usually happens beyond reloading book maximums - to someone who thinks manuals are written by liability lawyers.)

It's my theory that the jacketed bullet over-obturates at those pressures. The added friction compounds the pressure peak, which causes yet more obturation and so forth. If not for the movement of the bullet down the bore (increasing the effective case volume) it would lead to a catastrophic failure.

These things are only a fine line away from being bombs. If you're a reckless reloader, coldly reflect on that the next time you set your cheek against that "super" load.

Excellant info from all, thanks.

Without sounding like I love to take chances, would I be safe in assuming that it would be OK to use data from heavier bullets of the same type (lead, jacketed, etc) for reloading lighter bullets realizing that the velocities but not the pressure will surely be higher?
On a semi related subject, why is it that the most accurate "match" type rifle loads all seem to use hollow point bullets? It would seem to my uninformed mind that the hollow point would cause some turbulence and velocity loss that a true spear point would not?

Yes, if you have data for the next heavier weight, you are generally going to not have any problems with reloading. The only thing that comes to mind is that some very slow handgun powders (H110, 296), can in fact give erratic ignition when loaded too low. Pretty much anything else, I would not really worry a lot about.

Accuracy - because the back end of the bullet is what steers it. A hollow point moves the center of gravity of the bullet a bit farther back, vs. a soft point.

High speed photos of bullets in flight that show the supersonic shock waves, appear to show the start of the waves ahead of the bullet. It appears that the tip itself is riding behind the shock wave and not really a source of as much drag as you would expect.

It's also my theory that jacketed bullets cause rapid pressure jumps at top end, too. Have you ever seen or heard about velocity actually decreasing when powder charges pass a certain amount? (This usually happens beyond reloading book maximums - to someone who thinks manuals are written by liability lawyers.)

It's my theory that the jacketed bullet over-obturates at those pressures. The added friction compounds the pressure peak, which causes yet more obturation and so forth. If not for the movement of the bullet down the bore (increasing the effective case volume) it would lead to a catastrophic failure.

These things are only a fine line away from being bombs. If you're a reckless reloader, coldly reflect on that the next time you set your cheek against that "super" load.

Belive the same thing...once you pass the point of gross-deformation, jacketed or lead, the bullet starts to act more and more like a cork....harder you push on it, the higher the percentage of that push is transmitted as radial expansion...greater the pressure rise for less vel. gain. With lead, that point comes at a lower pressure than with jacketed (some very thin jacketed bullets do seem to get to gross deformation at lower pressures than the thick hard jacketed versions).

SO...belive that ALL bullets have some point were the pressure curve takes a steep rise...and that cast bullets find that sharp rise sooner than jacketed.