Nuther sizing die question from a noob......

Getting back up to speed after all these years, I'm beginning to understand why my Dad threw in the towel on loading for metalica and stuck with factory loads. Lots to learn and a lot of it confusing and contradictory. By comparison, reloading for shotguns was so easy even a child (me) could do it.

So doing my research on reloading techniques, I find references to fine tuning the sizing process by use of case comparators, including several helpful Utubes showing how. All say the goal when setting up your sizing die is to set shoulder bump back anywhere from .001 for bolt guns (we are talking rifles here) to as much as .004 for semi-autos. Do that and you wring out good accuracy, not to mention extend case life. Or so the story goes. Sounds like good advice, so I decide to put it into practice.

So yesterday, I'm setting up my sizing die for some .243.......carefully measure my case.....then follow directions for the dies.......which tends to go along the lines of...."raise ram on your press all the way, then screw in sizing die until it touches......lower ram and give it another 1/4 turn, then lock it down". I have 4 different brands of dies (Lee, RCBS, Hornady and Bonanza) and all pretty much say the same thing. Do that and your sizing die is set. No mention of getting that .001 shoulder bump.......but no worry, I can measure for that. So I do.......and what do I find? My shoulder bump is now EXTENDED by .001. Sizing the case does not decrease shoulder bump....it makes it longer?

My first thought is I didn't set die low enough, but quickly realize that once a die is bottomed out, it can't go any lower.

So what gives? Here is what I am thinking and if any of this is wrong, feel free to set me straight.

First is it seems to me that dies are made to form brass back to SAMMI specs. Both as to diameter and length. How much a die will size any brass thus depends on how much the brass needs to be worked. If fired in a loose, sloppy chamber, it may need a lot. I'm reading where military rifles often have chambers to the large size so most ammo will chamber and fire. Custom and other precision rifles being the other end of the spectrum and may not allow the brass to move much at all.

Second is it may take several firings before brass fully fire forms to a chamber. My assumption going in is would do that every time. That may be wrong, or it may be that the guns I'm loading for have tight chambers and are at min SAMMI specs and may not allow much case expansion? I know that for two of them, when I measure once fired brass in a Wilson case gauge, all brass still fits as to headspace and length. So basically, the brass I was sizing yesterday didn't need any shoulder bump. So how did it get longer? Only thing I can think of is the effort required to pull the neck sizer out was enough to also stretch the neck a bit with it. What I didn't do, but now realize I need to do is measure case length before and after sizing. Normally, I'd think of it as sizing forces the metal to go somewhere, but hadn't considered that the friction of pulling the neck sizer out would be enough to stretch the case with it.

But as far as setting up the dies for shoulder bump is concerned, one of the ideas that makes the most sense to me when using a bolt gun, is to strip the bolt......and if a fired case will not chamber, keep adjusting the sizing die down until the bolt will just barely close on a sized case. The only way I can see that happening with a normal die is to NOT follow the directions.......in fact, do the opposite. Screw the die down until it touches, then back the die up a half turn. Then start an incremental trial and error process until the the bolt just barely closes. That may be far less sizing than what the die instructions call for.

Or forget the technical stuff for now and just follow the directions to begin with? Where is the fun in that?

Attempting to measure bump using a Hornady case comparator.......mounted to my dial calipers. Measuring before sizing, and after. When I was trying this yesterday, I did not have a printout of the SAMMI specs for the 243 win, which is the only place I know of to find the published number for what the length to shoulder should be. If a new or once fired case is at or less than this number, I would not expect a full length die to have any influence on it........in other words, will give it "no bump" cause it doesn't need any. Which means it could be I was looking for something that wasn't there.

But it was about that time when I recalled someone on THR mentioned to me once that if a guy wanted custom dies made for a specific rifle, die maker would want 3X fired brass to assure it had fire formed to that chamber. It was about then the light came on.

Guess my point for even bringing it up is the fact that someone like me discovered the issue of shoulder bump, and attempted to do it, not knowing a whole lot of stuff needed to be known and understood in the middle. There is a pretty big gap or step between what the die maker's instructions are and what some folks are actually doing.

And yes I went from grade school level to grad school level and managed to skip past all that in the middle.

At this point, I have a pretty good start on what could be an entire chapter about dies for a reloading manual. The one I'm thinking of is my Lyman 50th. They left out a whole lot of good stuff that folks on this forum talk about daily.

Blue68f100 said:

What you see is the results of the body being sized make the brass grow. Once you over come this you start moving the shoulder back. So you just stopped too early. If you had continued you would have seen the shoulder move back.

Click to expand...

That was my first thought. If I keep lowering the die, I'll get some bump eventually. After one full turn.....I realized that once the die bottomed out on the ram, it would go no further. Ram simply stopped before handle could bottom out and raise ram any more. It only goes so far. There may be dies that do, but these were Lee dies, and once they bottom out, they will go no further. But the same appears to be the case with the RCBS and Hornady dies. They all only go so far.

It was about then I concluded that must be the situation with once fired brass that had not yet stretched to the point the die made any difference to it.

Have checked and verified that these once fired cases are fully bottomed out in dies. That, plus when I measure for case length, they are well below any need to trim, so beginning to suspect they simply have not yet stretched to the point where the dies are having any affect on shoulder bump.

Good learning experience however. Have a much better understanding of what the consequences are of following the die maker's instructions, vs. what folks are doing to get a custom fit of resized case to an individual gun.

BTW, checked my Lyman 50th again and there is a reference to all this in a topic called "Advanced Case Prep". Problem being I doubt an uninformed reader is going to gain anything from it. There is no background theory to get the reader up to speed, so the references to shoulder bump would only be understood by someone who already knew as much about it as the author did. Probably would have made for a good magazine article, but out of place in a reference manual. Missed opportunity.