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Old January 25, 2005, 05:50 PM   #1
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Seat depth variance

Hi guys,

I recently ran a batch of 10mm loads on the 550. As a final check, I measured OAL of each round. Max OAL spec is 1.260. I usually seat to 1.257 OAL. This allows for different brands, shapes of bullets. I use medium range loads so no signs of excessive pressure.

When measuring the latest batch, actual OAL varied from 1.249 - 1.257. The seat die is tight, clean and hasn't been moved in the last several batches. I know 8 thousandths may not make a huge difference on many longer calibers, but after seating then .003 short of published max OAL, the .008 of slop is making me wonder a little. Is 1.249 possibly/probably too deep ?

How consistent are your seat dies ? Do any of you get such a variance ?

Thanks for the feedback

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Old January 25, 2005, 07:41 PM   #2
Austin Charles
Join Date: December 16, 2004
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I get variance also. I think that it is the bullet, because if I measure the ogive they are a lot closer than the OAL. But still vary somewhat.
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Old January 25, 2005, 08:41 PM   #3
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1.249 shouldn't be a problem on anything less than really extreme loads. Make sure you are getting a good reading and not sometimes an errant bump on the bullet nose. What dies you using. If it has a sliding member, is it sliding fully? The bullets seating straight? What bullets you using. Using Hornady dies on a progressive press and West Coast round flat nosed plated 180gr I'm measuring +/- .001 or better with dial calipers. +/- .004 is not going to get the best accuracy. Is the bullet shape well matched to the "nose punch" or seating surface inside the die? Some dies have a flat and a conical die member.

Just an afterthought...are you fully seating your primers?

Last edited by Cal4D4; January 26, 2005 at 01:08 AM.
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Old January 26, 2005, 12:06 AM   #4
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The .40 isn't that sensitive, at least not where safety is a concern. Measure the bullets, and I'd be surprised if you didn't get .003 or better varience in some of them. Change the position of the Ogive, and the seating depth varies.

Also, if you load, say, 5 rds one at a time and measure them, I believe they'll be different than if you load them in the normal progressive manner with a shell in each station. I can only guess that with a shell in each station, the shell plate doesn't go quite as high, although I don't know why it wouldn't---I quit worrying about a few thousanths difference long ago. I believe there are other factors at work, also. Does it with other calibers, also.
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Old January 26, 2005, 10:15 AM   #5
Join Date: December 14, 2004
Location: Northwest NJ
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The max OAL is to assure proper function in the pistol. The min OAL is to assure thay you don't get excessive pressure. If you are a little short of the Maximum OAL, but still over the minimum OAL, you should be OK.
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Old January 26, 2005, 12:39 PM   #6
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I agree with Austin. I did a little experiment a while back to project theoretical variations in oal on my 45 acp rounds. To make a long story short, bullet olgive variation was the culprit in inconsistant oal's. One batch of bullets would give me a variation of .006" and another mfg's would give me .003". Although I've not run into it personally, I could see where an improperly matched seater stem could also give you variations, especially with SWC's.
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Old January 28, 2005, 02:30 PM   #7
Smokey Joe
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Seating depth issues

Whenever I'm having seating depth issues with lead pistol bullets, the first thing I suspect is a buildup of bullet lube in the seater die. That is usually the culprit--remove the seater from the die body, 2-3 swipes through with a cleaning patch with solvent, then a dry patch, clean off the seater too, replace it in the die body, and I'm usually back in business faster than it takes to tell it.

Anyhow, check inside your seating die for crud.
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--Smokey Joe
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Old January 29, 2005, 12:16 AM   #8
Join Date: October 4, 2004
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My $0.02 Worth

Only thing I would add to the above good advice, is to maybe substitute a plain flat seating punch, so the ogive shape becomes a non item.

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