Can you size down too much ?

[JonB_in_Glencoe]

SNIP>>>
Anyhow this leads me to a question I've been wondering while looking for a mold for my .270 win.
At what point do you say , hay this is just too much to size down ? Or does it matter if you can size it down in small incriminates at a time? Like would would something like a .284 down to .277-279 be too much of a stretch ?

First I'd say, "It all depends"
and then I'd say, "I think this is a question that only you can answer for yourself"
...
12 years I started a thread about this very subject, because I read the following from page 41 of the RCBS cast bullet manual #1.

Effect of Sizing
Experience has shown that each .001" of sizing results in about an extra inch of group dispersion at 100 yards. And don't think your barrel can size any better than your sizer/lubricator. It can't. The bullets must be perfect out of the mould.

I don't necessarily agree with this statement, but RCBS found it necessary to publish it, in their book.


https://castboolits.gunloads.com/sho...-less-accurate

[Shopdog]

Just sayin,if your processes bend or otherwise mishapes the bullet sizing it by .001...

Then that's sizing too much.

But let's say you had a way to size down .004"(random number) and end up with a bullet that is straighter than it came from the mould... then that amount isn't too much.

So,"it depends" a lot on the processes used.

[Shopdog]

In one of your other posts,about designing a mould(IIRC).... I wrote that you should bone up on the numbers that co uses in their "prints"... think NOE. So staying with NOE,look at their prints on the depth of the lube grooves. Another way to look/reference this would be,how tall the drive bands are. Use whichever makes it more clear for this next part....

Ask yourself about "sizing"... and consider "truing" as another way of expressing this. Not saying one is a better term... saying it may help you on your path. But back to "sizing" and drive band height. What effect does sizing down .004" have on the lube groove bttm? How does this change,with a change in band height(or depths if that's how you look at it)? Saying,we're hoping the .004" loss in diameter maintained or created a straight bullet... but if it didn't,how does this effect the inner core or groove bttm diameter compared to drive band concentricity. Hope you see where I'm going. You can easily move the center of pressure radially during a large(and can happen with small) sizing. Good luck with your project.

[beagle]

Again, "it depends". .003" is the accepted norm for rifles. After that, distortion sets in especially with base first sizers. With a nose first rig, you can get away with more. I've taken .458s in steps down to .450" to use in ML sabots. This was with pure lead which makes a difference too. I've taken .458s down to .452" and .454" successfully for pistols.
Fall back to the old adage; "You don't know what you can get away with until you try."/beagle