Variation in OAL

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ilikeoldguns

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I have finally started reloading .303 (FC Cases so far) and I am observing a 0.15 variation in OAL seemingly no matter what I do.

I am using a Lyman Universal Case Trimmer and a Lee 3-die set on a Lyman turret press. Best as I can tell my dies are nice and tight; i'm getting a full stroke on the lever and I *think* I am doing everything right with my trimmer; though frankly I find the Lyman Universal very fiddly; only seems to work through trial and (lots) of error, with no way to quickly return to any given setting. Not real fond of this item, but it is what I have at the moment.

I tried adjusting the seating and crimping die back and forth, but the variation remained. The result is that aiming for an OAL of 2.975 (lyman 49th ed), i am seeing between 2.85 and 3.0.

I am using hornady 150gr SP bullets, do those vary measurably in length that much?

What else could be going on that I am seeing this much variation?


Thanks for your time.
 
That's a huge variation. .015" would be something to work with, .150" now there's a serious problem. The only measurements that matter are case base to ogive and bullet base to ogive. As long as case base to ogive is constant you'll always hit the rifling the same way and as long as bullet base to ogive is constant you'll have the same case volume. Put some marker on your bullet and see where the seating die leaves tool marks. The closer to the ogive the better. Get a bullet comparator attachment for your calipers to make sure. Could be that your seating die doesn't make good contact with your bullet. I first used RCBS seating dies but I wound the seating stem was sitting on the very top of the bullet. I now use a Lee seater, it contacts with the bullet much further down.
 
So long as it is not match ammo for a target rifle and you are off the rifling, that variation won't make any real difference.

That said, you should figure out why.

One explanation (happened to me) is there were two different lot numbers of bullets in the same box, and they had different dimensions.
 
I'm finding that when reloading CamPro 9mm FCP RN ammo, there's a variation of up to ±0.005 in the total length of the bullet. I've measured anywhere from 0.526" to 0.537", avg 0.533" on a 20 sample.

Even using a seating die that is hollow (pushing around the ogive, not on the nose of the bullet), the best I can hope for is ±0.003" in OAL. So when I aim for 1.150", I'm happy to get anywhere in between 0.147" and 0.153" OAL and I still get the occasional shorter round. As long as the volume inside the case is about the same either way, I don't mind.
 
The 0.15 variation in OAL if correct , is excessive .
Are your primers protruding from the primer pockets on some of you brass?
Is there a noticeable difference in the tip profiles of the seated bullets , that may account for the variation?
As mentioned by others , Ogive measurement is the most accurate measurement for OAL.
Has you vernier calibration / zero drifted to create the error?

You are using a Turret press . Is there any noticeable flex when seating the bullets , that may account for the inconsistency in OAL?
Do you seat all of your bullets at the same time without changing stations on the turret press? If not the inconsistency may be caused by the turret index ball not returning to battery between stages.
 
Well, I'm pretty sure I'm reading the calipers right, but they are drafting digital calipers; not specialist reloading calipers and I am seeing between 2.85-3" OAL
 
SOLVED IT!

Went back and re-checked my trimmer and press, but...

My calipers were broken; well bent really. Not sure when or how it happened, but the one prong was very slightly bent and i was getting different readings when I measured the rounds at different points.

I am still long, but only by about 0.020-0.023 and I have switched to newer pair i had picked up at a garage sale some time ago.
 
ilikeoldguns said:
SOLVED IT!

Went back and re-checked my trimmer and press, but...

My calipers were broken; well bent really. Not sure when or how it happened, but the one prong was very slightly bent and i was getting different readings when I measured the rounds at different points.



I am still long, but only by about 0.020-0.023 and I have switched to newer pair i had picked up at a garage sale some time ago.
Click to expand...


Are you positive those garage sale specials are bang on......we are working in fairly precise measurements

Cheers!!
 
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