# Seating depth



## Savage260 (Oct 21, 2007)

I was just loading some 140gr SMKs into my 6.5X284 Norma brass and noticed after about the first 12 rounds my seating depth started to bounce all over. The first 12 were 3.480 ogive using a dial caliper and Hornady bullet comp. The depth after that was mostly at 3.480, but some dropped into the 3.473-3.476 range. Any ideas why? I didn't do any thing different with the die, I was pulling the ram the same every time, what did I do wrong? I have had depth move around .002 up or down, but not .005 or more. I need to keep these pretty close so when I find a good load I can start looking for the lands by the .001.


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## Csquared (Sep 5, 2006)

Is the powder compressed?


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## Savage260 (Oct 21, 2007)

No these were low to middle of the road loads. Not even close so max yet. NDTerminator suggested there might be a bit of debris that didn't get cleaned out of the die. I am not sure if that is what is going on, but I will clean the die again.


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## MagnumManiac (Feb 19, 2008)

The most common reason for the discrepancy is due to the ogive being different from base to tip, this will cause a different OAL. The seating die seats off the ogive of the bullet, not the tip, and this is why it will change. I have had bullets out of the same box measure differently from base to ogive!
I wouldn't worry about it too much unless there is a big difference in accuracy between the 2 OAL's.


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## Savage260 (Oct 21, 2007)

Great, now I am all confused! I have read and been told the ogive measurement was the best to take because it would be more consistant than base to tip due to variations in tip lengths. Shouldn't SMKs be pretty uniform if they are match bullets?


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## AdamFisk (Jan 30, 2005)

Savage260 said:


> Great, now I am all confused! I have read and been told the ogive measurement was the best to take because it would be more consistant than base to tip due to variations in tip lengths. Shouldn't SMKs be pretty uniform if they are match bullets?


Yes, they should be more uniform because they are match. I can't remember what the tolerances were, I just read it in my Sierra manual the other day. I'm thinking 1-2 thousandths of an inch in their matchkings, measured from ogive.

So I don't think it's the bullets causing your inconsistent OAL's.......I was having the same problem while measuring from the bullet tip. I bought a comparator and took Plainsman's advice and cleaned my die, now I'm only off 1-2 thousandths on an inch, with Gamekings.


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## Savage260 (Oct 21, 2007)

I don't know what is going on then. The die is clean, the bullets are supposed to be uniform, the brass is all trimmed within .001, and the headspace all measured out within .002. Can any one think of any thing else?


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## Plainsman (Jul 30, 2003)

If your measuring from the tip you will find that the metaplat is perhaps the least uniform part of the bullet. Many bench rest shooters will purchase metaplat uniform tools. Evidently they think the uniform tip is more important than loosing two or three grains of bullet. The most important part of the bullet is the base, and that in combination with a good crown on your rifle are perhaps they most important key to accuracy. It is why you always place the sprue of a round ball upwards when you load a muzzleloader. 
You will not get consistent measurements from the tip no matter how expensive your match bullets. Lead tip bullets are the worst, and polycarbonate the best, when measurements are taken off the tip.


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## Savage260 (Oct 21, 2007)

The measurements are all taken from ogive to base via hornady bullet comp and dial caliper.


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## Plainsman (Jul 30, 2003)

Savage260 said:


> The measurements are all taken from ogive to base via hornady bullet comp and dial caliper.


That should be very accurate. Dirty dies, neck tension, primer not fully seated, casing bent at base, etc. There could be a few explanations. Some of those things take time to figure out even when your at the press yourself.


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## Savage260 (Oct 21, 2007)

I was thinking about neck tension, it seemed like the ones that were seating deeper almost slid into the case with a lot less friction. But how would that make them seat any deeper? If the die is set to a certain level, and the cases are the same length, the bullets are supposedly the same dimentions, I don't get it??? I can't push the bullet down into the case just using my hands so the tension must be pretty good.....or am I wrong on that? This is my first time really trying to load every thing for accuracy, every thing before has been hunting loads, so it really bothers me!


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## Plainsman (Jul 30, 2003)

I think you get some rebound with a very tight neck. I say that because I have found that if I have a very tight neck tension and run the loaded round through the bullet seating die a second and third time they will often become one or two thousandths shorter. The same thing doesn't happen to a case with a lighter neck tension. That means something, but I am not sure what. My guess is rebound. 
Next time you find one that is long run it into the bullet seating die, then back away slightly and seat again two, three, four times and measure. I would be curious to see what you find. My guess is you will get higher velocity with those that have tighter necks. Do you find that the longer loaded cartridges are of a particular brand?


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## Savage260 (Oct 21, 2007)

This is my first time loading for the 6.5X284. All the brass is new Lapua, the bullets are all 140gr SMKs. I put together another set of loads yesterday, and had the same thing happen. 5-6 out of 20 were shorter than the rest. These were all run through a neck die, so they shouldn't have different neck tension should they?


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## SaberX01 (Sep 25, 2009)

Having spent a fair bit of time chasing these ghosts myself, I can say there is "no silver bullet" ( pun intended :wink: ) for finding the root cause. However, there are a number of variables, as other folks have said, that contribute to the problem.

Things I've found in the past which have contributed to the problems are, noting, it's a systematic process of elimination. If you eliminate what it "Is Not" your left with what "It Is", or so those in the know say is truth. It may also be a combination of several factors, none of which on their own would be the root cause.

- The Bullets Themselves: Even match grade bullets have some level of variability. Usually, as others have stated, its small within lots, but can contribute. Unless your using Custom Swaged Rounds, you can expect that bullet sorting will be necessary to eliminate a portion of inaccuracy. This amount of inaccuracy can vary from lot to lot, even with Custom Swaged bullets.

- Case Prep: It's a given that Lupua and Norma Brass are some of the best in the business. However, this does not make them immune to variability. For extreme consistency, full case prep, pre-sort weights, neck measuring, thickness & uniformity trimming will all help to improve concentricity & consistent neck tension. Without a concentric load, your Ogive OAL measurement will induce a length error. Bottom line is, if your loading for accuracy and the best possible consistency, full case prep, new or reused is a must. Without doing so, it's difficult to identify the step or results that can or are the contributing cause to an error.

- Primer Seating: As others have stated, inconsistent primer seating depth can contribute to inaccurate depth measurements. If your sure this is not contributing, eliminate it as a contribution cause.

- Shell Holder Quality: It's a mute point to strive for accurate load lengths if the platform it's being compressed against is flawed, and as we all know, this starts with the shell holder. Check and / or change it to a different brand and compare results.

- Ogive & Meplat: Although using an OAL bullet depth gauge to measure the bullets before loading, this does not mean the Ogive itself is concentric. Without this being correct, the gauge is going to provide an inaccurate measurement, as it will ride on the highest point along the Ogive. This cane be checked and corrected by using a bullet tipping die such as those from Bullet Tipping; http://www.bullettipping.com/bullettippingdie_detail.asp. Obviously, the Meplat will not affect the OAL gauge as it rides on the Ogive, but it's always good to square the Meplat after tipping to increase BC consistency.

- Press Length - Die Considerations: If your not getting a consistent upward travel, obviously seating depth accuracy will suffer. I can't say I've ever found the press itself to be a contributing factor, but Die to Die variability has come into play. Often times changing your seating Die will tell the tale here. I use Readding Comp. Seating Die and since shifting to this die, I've rarely had seating depth issues, all other things being equal. Having only 5 to 6 per hundred does not scream die trouble, but it can't be ruled out until you elliminate it, and the only true way I know is to chage to a diffrent die and compare results.

From my trouble shooting notes, that's all I have against seating depths itself. A few resources I've used int the passed for Case / Level loads are as follows:

Bullet Seating Depths: http://www.gunnersden.com/index.htm.rifle-reloading-bullets.html
Long Range Load Development: http://www.6mmbr.com/laddertest.html
Match Case Prep: http://www.6mmbr.com/JGcaseprep.html
Richardson's DVD - Reloading For Accuracy: http://richardscustomrifles.com/instructionalvideos.htm
Sinclair's - Determine Seating Depths: http://blog.sinclairintl.com/2009/03/26/determining-bullet-seating-depth/
Forums: Many Such as North Dakota Outdoors.

If you nail it down, let us know what the culprit was / is, i'd be interested in reading how you found and resolved it.

Have Fun, Be Safe and Enjoy Handloading


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## People (Jan 17, 2005)

You may want to do some annealing of your brass. If it is inconsistant that can cause different ammount of AOL. Some will slide in easier than others. Just one more think to look at.


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