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Old February 18, 2015, 12:26 AM   #1
Willkk
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Seating depth

I have been loading some hornady interlock btsp and cannot for the life of me get these to consistently seat at 3.210 per the manual. I keep getting 3.203, 3.214, 3.206, etc. Could it be my die? I never had this issue with my Speer bullets. Is it going to be inaccurate at those variances?
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Old February 18, 2015, 03:07 AM   #2
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It really won't make any difference at all

The COAL that performs best varies from gun to gun, and the length given in the manuals is just the "industry standard".

It often pays to find what length works best in your gun, as long as it will fit the magazine and function reliably.

One thing that helps is to be as consistant as possible in how you operate the press. I like to seat the bullet, then rotate it 180 degrees and seat it again.

http://www.larrywillis.com/OAL.html
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Old February 18, 2015, 05:56 AM   #3
Nathan
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RCBS die? Not sure why, but I have only noticed this with RCBS dies.
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Old February 18, 2015, 06:01 AM   #4
hartcreek
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The problem is that the seating die cone contacts the bullet in one place and seats the bullet yet you are measuring to another place the bullet tip. Take a buch of bullets out and measure them you will find a deviation.
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Old February 18, 2015, 08:03 AM   #5
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Also might try tightening your lock ring on the bullet seater punch when the ram is at the top of stroke so that the seater punch stays centered as it is tightened. May give a more consistant (and concentric) fit on the bullet tip. jd
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Old February 18, 2015, 08:06 AM   #6
cdoc42
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If you are measuring from the tip of the bullet to the base of the case, variations will occur if the lead tip is deformed in any way. As well, if you are testing two different manufacturers, but the same weight, measuring from tip to base is an inefficient way to get to the best accuracy.

Hornady, as well as Stoney Point, makes a set of caliber specific attachments that lock onto your caliper. Then you measure the bullet from the ogive (i.e., point where the diameter = the point of contact with the rifling) to the base. This much different than tip to base.

Two 130gr bullets from Hornady and Speer will have an ogive in a different place. In fact, I have found Speer 130gr BT differs in measurement from Speer 130gr flat base in .270 Win.

Now, even with this greater degree of specificity, I often find I can't get every round to measure exactly the same. If the desired seated round is 2.835" I may have ranges from 2.832 to 2.837. You can "feel" this difference when you are seating the bullet. If it seats with less resistance you can bet it will be deeper. If there is more resistance, it will be longer. It depends on the age of the case, i.e., how many times it's be reloaded, the thickness or hardness of the neck, etc. On a practical basis it doesn't severely affect accuracy unless you're looking for consistent 0.5" groups.
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Old February 18, 2015, 10:10 AM   #7
Bart B.
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The bullets jump distance to the rifling will vary a few thousandths if all rounds have the exact same OAL. The pointing die that shapes the front half of the bullet doesn't make all of them exactly the same shape; there's a few thousandths spread.

A few thousandths spread of how far bullets jump to the rifling is not a concern. .308 Win match ammo's shot sub 1/3 MOA at 200 yards for 3000 rounds of barrel life and the last shot jumped 1/10th inch further to the lands than the first one did. The rifling erodes away about .001" for every 20 to 30 shots fired; bullet jump distance increases at that rate.

It's more important for best accuracy if the bullets are about .0005" larger than the barrel's groove diameter than if they've got ten times that much difference across how far they jump to the rifling.

Shoot your ammo more than you measure it. Life's better that way.

Last edited by Bart B.; February 18, 2015 at 10:22 AM.
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Old February 18, 2015, 12:04 PM   #8
Unclenick
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WillKK,

I once took 15 Sierra 150 grain MatchKings and measured a spread of 0.0135" in length from the base to tip, at a standard deviation of 0.0033". The same set of 15 bullets measured from the base to ogive with a Sinclair throat-like insert contacting the ogive down where a barrel does, measured a spread of 0.008", with a standard deviation of 0.0025". This is the shape variation Bart's talking about. It's the reason Bryan Litz has measured about 3% variation in ballistic coefficient for bullets coming out of the same box. The only ones with more length consistency are the plastic tipped ones, and that's because s machine trims the bullet tip uniform before the plastic is inserted. But the bullet will still have that ogive variation, which is what affects fit in the gun.

Since the seating die presses down on the ogive, but at a higher location than throat contact, where the variation is a little greater, it usually gets the cartridge base-to-ogive variation down to within a couple of thousands or three.

In general, the overall cartridge length is just important to how the cartridge fits into and feeds from a magazine. I've never run into a magazine that can't accommodate cartridges being a hundredth or two too long, so bullet length variation has been a moot issue for me. Just check that this is true for your magazines rather than assuming they are like the ones I've had. Accuracy of some gun and bullet combinations is affected by the jump to the lands, but you have to try this out to see if it matters for your combinations or not.
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Old February 18, 2015, 03:29 PM   #9
cw308
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Get yourself a Hornady Comparator, will measure from the base to the bullets ogive. First measure your OAL the way your diong now, then attach the comparator to you caliper and measure to the ogive. when measuring to the ogive your settings will be exact. Make sure your first OAL will fit your magazine. I load 1 round at a time, benchrest shooter,so I only care about base to ogive setting.
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Old February 18, 2015, 03:50 PM   #10
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Quote:
I once took 15 Sierra 150 grain MatchKings and measured a spread of 0.0135" in length from the base to tip, at a standard deviation of 0.0033"
There will also be a lot of weight variation

If I'm really bored when I open a new box of bullets, I will sort them into three piles according to overweight, underweight or "Goldilocks"
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Old February 18, 2015, 05:36 PM   #11
Navistar
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My Lee die has been very accurate and consisten with round nose. I have no experience with hollow point yet.
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