OAL length help. Why such a variation?

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Ghost In The Fog

Ghost In The Fog

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Alrighty- Here's a question for all of you.
Below is something that is very puzzling to me and I can't figure out.
I am using a Lee Classic Turret. I have listed the empty case lengths and then the case overall length after loading with Berrys plated 115 gr. RN. Why such a variation?
Shouldn't they all be the same within a very small tolerance?
The ram goes up to a fixed position and meets the seating die that is also in a fixed position. This is for 100 cases and below is the starting overall length of the empty case and then the low and high caliper readings. All were loaded at the same time.
I am new to all of this. Am I just being overly cautions? Why the differences in length? Is this normal?
I have had zero issues with feeding in my guns or anything else for that matter.
Berry's recommended 1.130 COAL
It seems the longer the case, the shorter the overall length of the finished bullet. Why? :banghead::banghead::banghead:


Thanks for your help.



Empty
COAL Short Long Variation
0.744 1.127 1.133 0.006
0.745 1.132 1.133 0.001
0.746 1.128 1.134 0.006
0.747 1.117 1.134 0.017
0.748 1.118 1.127 0.009
0.749 1.119 1.127 0.008
0.750 1.129 1.136 0.007
0.751 1.122 1.126 0.004
0.752 1.120 1.124 0.004

1.235 to 1.130 is the overall low and high average
 
The .017" is not normal. Turret or progressive OK to .010" A single stage press should do better with a max of .005" Lee has the answers - http://leeprecision.net/support/index.php?/Knowledgebase/List/Index/13/product-support
Knowledgebase: Reloading Dies





Overall Length (OAL) Variation

Posted by on 20 October 2011 07:43 AM

There are a number of possible causes for overall length variation. One is the way it is measured. If you measure overall length from the tip of the bullet to the base of the case, remember to subtract the variation due to bullet length tolerance. The bullets will vary in length due to manufacturing tolerances (bullets with exposed lead noses are the worst in this regard) and this will add to the overall cartridge length variation. Remember that the bullet seater plug does not (or shouldn't) contact the tip of the bullet when seating, but contacts farther down the ogive. For a more accurate seating depth measurement, take the seater plug out of the bullet seating die, place it on top of the cartridge and measure from the base of the case to the top of the seater plug.

Another possible cause for bullet seating depth variation is seating and crimping at the same time when trying to apply a firm crimp to untrimmed cases. Variation in case length also causes variation in the amount of crimp applied. Long cases get a heavier crimp than short ones. When seating and crimping at the same time, the crimp is formed as the bullet is seated into the case. The crimp will form sooner on a long case, and therefore the bullet will not be seated as deeply. The solution is to seat and crimp in a separate step (the Lee Factory Crimp die is good for this) and/or trim cases to a uniform length.

The amount of force required to cycle a progressive press varies with the number of cases in the shell plate. When the shell plate is full, it is harder to lower the lever than when there are one or two cases present. This can lead to variation in cartridge overall length because there are different loads placed on the working parts of the press. When the shell plate is full, seating depth will be slightly long, because the load is higher and all of the clearances are taken up. With the shell plate nearly empty, the load is not great enough to squeeze out these clearances, and the seating depth is short.

A potential solution for this on progressive presses is to turn the sizing die in far enough so that the carrier is stopping on the bottom of the die. This removes clearance problems when no sizing but yet seating / crimping is occurring. Take special care not to turn the die in further than to just touch the shell plate and possibly just a tad more. About 1/4th of turn more is all you want to go, turning the sizing die in too far causes other problems.
Click to expand...
 
Mixed brass.

The differing case length has nothing to do with it though. It is the amount of neck tension causing your variance. Tighter cases will make longer rounds as the bullet smashes against and deforms into the seating plug. Sorting your brass should tighten up your tolerances. A custom seating plug would help too.

Or do nothing and keep doing what you are doing. Unless you are hotrodding the load you are not gonna notice much difference, as you already mentioned.
 
What brand of seating die ?

And can you run another batch, record the sequence and measure the AOL as the rounds come off the press ?

A Lee bullet seater has no lock ring on the seating plug. It has a rubber o-ring, and it is possible for the plug to screw itself out very slowly while reloading, so the first rounds loaded measure slightly shorter than those at the end of the session.
 
Ought to be more like a .005 spread, or a hair more for bad seater stem to bullet fit. Case length has nothing to do with it. Nek tension can if the press flexes a lot.
 
Make sure your primers are seated a hair below the case head, so you are not measuring off a high primer.
 
Just for fun I would measure some of the bullets to first to see how much difference you have there.
It could also be due to where the seating die contacts the bullet even if the bullets show little difference in OAL.

I have the old Lee "Deluxe" turrent, I use the Lee seater and crimp with the FCD and normally results (assuming the bullets are consistent) are usually < + or -.01 with mixed untrimmed range brass.
While a turret will not be as accurate as a Single stage I get good SDs and ESs and ammo that shoots as good as I can off mine.

Maybe being lazy on my part but since I don't load MAX charges I set the OAL measure a few, load a bunch, measure a few don't seem to have issues.
Another just for fun, move the dies to different holes in the turret to see if you get better results. (seater/crimp in a different hole)
Round nose bullets can be a pain to measure OAL, (guessing you measured more than once on the one that was off by .017?) one reason I prefer cones or a flat nose. I like the RMR 124 flat nose.


Is this mixed brass? Are all the cases the same length the same brand/batch with the same number of reloads?
Averaged out you differences work out to .0068 not great not bad. The one(s) that were .017 are what throws the average off. Without the .017 your average is closer to .0056.
if you measured a bunch it would be interesting to see all the numbers. (it appears you measure multiple ones for each case length) Maybe just the one round that was more than .01 off?
I myself would not worry about .01 unless you are loading max charges but .017 is concerning.

http://www.shop.rmrbullets.com/9mm-...1C6B646204B7FAF33B29EEA09EB26C.m1plqscsfapp04
RMR offers THR member a 5% discount and their price includes shipping.
(they also have them in 250 qty a hair more per bullet, and 1000 qty a hair less per bullet.)
If you are interested in trying the flat nose PM me and I will be happy send you a some to try.
 
Last edited:
Walkalong said:
if the press flexes a lot.
Click to expand...

Bingo!

My reloading bench is not 100% solid and it does flex and bend slightly when operating the press.
I have very limited space and I am also very, um... frugal? Okay, down right cheap. ;)

This makes perfect sense. The bench flexes, even slightly, then that would have to affect the press as well.

I bought a small bench and until I was absolutely sure I was going to really stick with this, I went on the small and inexpensive side because I would have no use for a work bench in my basement if was to stop reloading.

I would bet that you are right on the nose with this.
It is all good information and there is so much to learn. Looks like I will be building a new reloading table.

Thank you thank you thank you.

I will also keep up and check all of the other great suggestions.
Thanks everyone.
 
Just to clarify again.

Empty case length has nothing at all to do with finished OAL of the loaded round.

Consider that the shell holder is pressing on the bottom of the case.

And the seating die stem is pushing against some point on the bullet ogive, or radius of the nose.

A long case, or a short case will end up having the same OAL.
Just more bullet will be seated inside the long case.

As for your problem???

It sounds like the bullets you are using have quite a bit of variation in ogive curve.

So your seating die is pushing on them in slightly different places.
And the OAL comes out different when you measure case base to bullet nose.

For an accurate measurement of press accuracy, you have to use a bullet comparator to measure off the ogive, where the seating stem contacts the bullet during seating.

rs_sinclair_hex_style_bullet_comparators_a.jpg

rc
 
Not much experience under my belt, and you may have other issues. But one thing I found with a similar issue, just not as wide of swing, is when you seat the bullet try to use the same force and speed with each bullet. I found if I go real slow and easy compared to firm and controlled my OAL will be longer. Also had issue with neck tension at first and even after I crimped the bullet could be easily pushed all the way into to case. Was using cleaned primed brass that did not have the proper sizing.
 
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