...so, I did some handloading the other day for my 7mm RM, in 140gr and 160gr bullets. I was surprised to see that the 140gr called for a larger powder load than did the 160s. Looking through the Barnes manual, it seems that this is true for many, but not all, cartridges.

Can someone tell me why it is that a lighter bullet needs more charge? Thanks...

It's not that a lighter bullet needs more powder, it's that the pressures with a heavier would be excessive.

Can you elaborate? Excessive how? Wear and tear on the rifle? Danger? Inaccuracy? All of the above?

it's purely a matter of pressure. The heavier bullet accelerates slower (law of physics) and leaves less room in the bore in which the burning powder (gases) can fill so in order to keep pressures in line the amount of powder is reduced.

A heavier bullet usually has a longer bearing surface (the part of the bullet that actually touches the barrel), & longer heavier bullets take longer to exit the barrel as vapo said. This means you need to use less powder of the same burning rate under a longer/heavier bullet. This is pretty much true for all cartridge reloading from pistol rounds to the biggest rifle rounds.
As Steve said, you don't need more powder for a lighter bullet but you CAN use more powder to get higher vel. Yes, using data for 140gr bullets w/ 160gr would be a dangerous pressure overload. Not to be a wise ass , but it sounds like you need to do some more reading on the subject of reloading. This is important info. you should know BEFORE you start putting powder in cases.

quote:

Originally posted by mzimmers:
Can you elaborate? Excessive how? Wear and tear on the rifle? Danger? Inaccuracy? All of the above?

The summamabitch could blow up in your face.

While you're reading the loading books to get educated.
Compare the loading tables, velocities and bullet weights available between the 7mmag and 30'06.
Doubt you'll see any benifit's at all to have a 7mmag. OTHER than having a MAGNUM!! That is better, right?? hehe!

Oh yeah, I had to learn the same thing the hardway too.

George

Yeah, before I bought my rifle, I did that and discovered pretty much just what you said. The 7RM and the 06 are really close in all the major categories (including recoil). I got the 7 because I wanted a Sako, and I'm left handed. Used LH Sakos don't exactly grow on trees, so when this came by at a good price I snagged it.

I'm not sure what you consider learning the hard way; I've yet to experience a downside to this rifle.

zim, don't let anyone put you off on the 7mag. It's a great caliber, a bit better @ long range than the 06 but then again, that was what it wadesigned for. A 160gr bullet @ 3000fps is good medicine for just about anything in NA.

Thanks, Fred. I figured George was coming at me off the wall, but it's a slow morning, so I bothered to reply. There is some truth to what he said, though -- when I was book-evaluating various cartridges, I discovered how similar in velocity and energy many of the mid-range calibers are.

This is currently my only rifle, and it's hard to imagine needing another one. If I get spunky and decide to head for Alaska, I might think about something bigger, but then I might as well go way up, like to a .375 H&H. I see no point in going to a new caliber that's only going to offer a 10% or so change in performance.

Anyway, I'm really pleased with my 7RM. It's a much better rifle than I am a shooter.