Adjusting FL Die -- Weird Results

[Brian]

I don't understand what's going on here, and I hope someone can help me.

When I place an unfired piece of W-W 6 mm Rem brass in my RCBS Precision Mic, the case is at "zero," as it should be.

When I place a fired case in the Precision Mic, it shows an increase of .005 - .007, which is fine.

I have no problem using my Redding neck sizing die to punch the primer and resize the neck (or the last 2/3 of it, which provides me with great accuracy and the reloaded round chambers just fine, albeit with slight resistance).

But I can't get consistent results if I try to FL resize my cases. I've started my FL sizing by following Redding's directions, i.e. to screw the die in to the point where it just touches the shell holder when the ram is completely raised. With the die so adjusted, the shoulder usually remains where it was when the case was fired, though sometimes it is bumped backwards by .001 - .002 in, and sometimes the shoulder actually seems to move forward by .001 - 002.

When I screw the die in slightly (1/8 - 1/4 turn) so that it adjusts a given case back to "zero" subsequent cases may remain increased .005 - .007, while in others the shoulder may be bumped back slightly-to -greatly down towards zero (good!), or actually overshoot zero. (So some cases end up with the shoulder at, say, +.003, with others going down to as much as —.003).

The bottom line is that although all cases start with their shoulder at the same point, and with the die adjusted and locked for one case, other cases may not be resized to the same dimensions, the extreme spread reaching 0.010 inches. All of these cases chamber with no resistance.

I'm careful with my lubrication, and make sure I clean the inside of the neck, and even lube it a little. I'm baffled. Any thoughts?

Thanks.

Brian

 

[SOTN]

Brian:
I would guess, that you are not getting consistent sizing from your die, and press combination.

If you are using a light press, for the operation, and there is enough FLEX in the press, you may not be getting the case into the die all the way, every time.

Of course, it could be, that some of your brass is harder too, or perhaps over-expanded.

Maybe, your die isn’t a good match for your rifle's chamber, and has to be over-adjusted somewhat, to size enough.

When Full Length sizing, it isn’t uncommon to see your shoulder grow in length, when it is sized down around the outside. The brass has to go someplace, so the shoulder moves forward. You may have to completely Full Length Size the case to bump the shoulder.

I say the above, because I had the same problem, and I know it can happen. I went to a heavy cast iron press, and it made a world of difference. I also had to make sure I had enough lube on the base of the cases, and throw away brass that was over-expanded from too-hot loads.

Some people talk about how the expander can pull the shoulder back forward again. I’ve never had that problem that I know of, and it wasn’t the cause of the problems I was having with dies for different cartridges. My problems were mostly due to the light-weight presses, I was using, for cartridges that required a lot of sizing power.
Smitty of the North

 

[rick smith]

Brian, first you don't need to get the case back to "zero", you only need to bump the shoulder back by 0.001-0.002" once it gets tight in your chamber. Taking it back to zero will shorten case life and will eventially cause case head seperation. Try the search mode and look for PFL or partial full length sizing. There are several things that will cause your problem SOTH covered some of them. Dies, presses, shell holders, expander bottons, lube problems and the biggest known problem "Operator Error", also the hardest to correct. :lol: Rick.

 

[Brian]

Thanks, guys. I'm going to go back to the bench in the next day or two and try again. Smitty, I don't think a springy press is the problem. I have a Rockchucker. Also, I don't think the expander button is the culprit either, because when I neck size, the shoulder datum doesn't change position.

Rick, I myself may well be the problem, but I can't see how. On the other hand, I can't see how anything that's as precise and unchanging as precision dies tightly screwed into a press could account for what I'm seeing, either. Which leaves me with the cases, which Smitty suggested. (Rim thickness? But that seems unlikely, since when I seat my bullets, the "slop" there is only ± .002 or so.)

More bench work might help.

I'm finding myself being fascinated by what is surely a purely academic problem. I almost always neck size, and the few times I've FL or PFL sized, I simply set the die per instructions, measured a single case and adjusted the die accordingly using that case again, and after resizing, made sure the all cases chambered easily. This is the first time I've measured every single case before sizing and then again afterwards in an attempt at consistency.

I'll post again when I've done some more work.

I really appreciate your thoughts. Thanks again.

Brian

 

[rick smith]

Brian, do you use the same expander button in the FL and Neck die? If I have to use an expander button, I will polish them to a mirror finish and use a dry lube. My normal die sets, if available, a body die, bushing neck die(no expander), and a competition seater. Moved from a Rock Chucker to a Forster Co-Ax many years ago. Still use the RC for some tasks but the bulk of my rifle loads are on the Co-Ax. Screw in dies can have an effect do to the amount of tightness.
Run various test to find what works best for you.Rick.

 

[Brian]

Okay -- I've done some more cases, and I think I can account for much of what's going on.

Though the brass is all W-W, it represents at least two different batches, purchased years apart, which I'd mixed. I believe that the two different lots had rims of different thicknesses, which could account for .002 --.003 of what I've seen.

To determine this, I sorted FL sized brass into two groups, one that measured +.005 with my precision mic, the other which was .000. I then adjusted my seating die so that it seated the bullet to a Stoney Point comparator length of 3.365 for one case. All of that group (n=15) ended up measuring 3.365 except for two cases which didn't exceed 3.366.

I left the die as it was, and seated bullets in the second batch of brass, and they most measured 3.363, with several measuring 3.364+. So there was no overlap between the two groups, and I attribute what little variation I did see within groups to variation in the location of the ogive of the bullets (58 gr Hornady VMax). I can think of nothing that would account for this other than differences in rim thickness.

I also think that I didn't apply enough pressure to the ram to fully get the case into the die.

Here's the story. When I raise the ram, I use a firm and continuous pull on the lever, and stop applying pressure when it bottoms-out, which may or may not involve some camming over, but always seemed definitive. That leaves me with a shoulder of, say, +.004 in my Precision Mic.

But if I force the lever down after it's seemingly bottomed out, I can reduce that value to +.002 -- +.003. The only way I can account for this is that it was "operator error." That what seemed to be the extreme of movement was in fact not, and I didn't recognize that.

Probably more than you ever wanted to know . . . but there you have it!

Thanks much for your time and thoughts.

Brian

 

[Jaywalker]

You might also consider that when you adjust the die to the general dimensions, it isn't really set to your chamber and may not be actually bumping the shoulder back at all. (Usually is, but not always.) If it doesn't bump the shoulder, the brass that was expanded in firing still has to go someplace - the shoulder then moves forward, counterintuitively.

Jaywalker