Reloading Issue: Why do measurements vary?

[TennJed]

I also see variations in the bullet construction it's self …. If you measure every bullet you will see as much a cpl thousands difference. I had two identical boxes of nosler Custom Comps (same cal. same weight) there was 14k difference in bullet length between the two boxes, but the weight was spot on….

I now verify those numbers every time cause you never know, if you're loading BTO I guess it shouldn't matter that much. But, it did make me scratch my head…

+1 for bullet variance. Measure the bullets from the ogive, not OAL, and there will probably be several thousands difference in the measurements. This translates into the seat die pushing in different locations on the bullet.

 

[LaHunter]

You have to remember, the seating stem contacts the bullet in a different location than your comparator. So micro differences in the bullet ogive will show up in your cbto measurement.

 

[Koda_]

Reloading any cartridge, when you finish seating the bullet and measure successive fully-loaded cartridges, the measurements should be identical. That is, the distance between the shell holder and the bullet seating die are a constant. So regardless of variations in cartridge case length and carrying bullet lengths, the overall length, Cartridge Base to Orgive should be constant. This assumes no "stretch" or play in the loading machinery. I notice this in all different calibers. What am I missing"

Because seating dies use the bullets ogive not the tip.
Measure yout CBTO distance and they will all be the same, compared to the COAL.

I find the COAL can vary up to .010" but my CBTO is within +/- .002"

 

[vancewalker007]

Thanks all of you who contributed to the confusion. Yes, I recognize all the variations talked about. BUT, the distance between the shell holder and the seating die SHOULD be consistent. If that distance is consistent then cartridge base to bullet orgive should be consistent. UNLESS something happens to shrink or expand that distance AFTER the bullet has been seated. Powder de-compressing, brass somehow pinching bullet outward...might have something to do with it. That exhausts my imagination on the subject.

This isn't exactly true. What's happening is the max height of the bullet stem can move will sometimes be hit and sometimes it will not, depending on the length of the stuff you're sandwiching between it and shell holder.

 

[L.Sherm]

Bullet seating dies do not seat on the ogive. Consistency in bullets can and will contribute to in Consistency its one of the reasons I shoot Bergers.
If you have consistent bullets and the correct seating stem for your bullet the biggest contributing factor is brass neck prep after that.
Let me rephrase seating on the Ogive, it does seat so to speak but way ahead of were the Ogive contacts the lands and thats were consistency needs to be.

 

[orkan]

the distance between the shell holder and the seating die SHOULD be consistent. If that distance is consistent then cartridge base to bullet orgive should be consistent.

You're not getting a very critical aspect of this. Just because the distance between the shell holder and die are consistent, doesn't mean your output is consistent. Right down to the uniformity of velocity that you're running the handle with. All of the other variables stack to deliver the final result. This is why it's so easy to spend so much money on the reloading bench on high end presses and gear. The variables matter individually, then they stack, so making improvements everywhere in the process in the aggregate can have a large effect on final dimensions.

The better gear, allows you to hold a better tolerance, faster.

If you need, you can always give me a call and I can explain it with better detail.


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[Koda_]

Bullet seating dies do not seat on the ogive. Consistency in bullets can and will contribute to in Consistency its one of the reasons I shoot Bergers.
If you have consistent bullets and the correct seating stem for your bullet the biggest contributing factor is brass neck prep after that.
Let me rephrase seating on the Ogive, it does seat so to speak but way ahead of were the Ogive contacts the lands and thats were consistency needs to be.

To clarify, your saying it does indeed seat off the ogive and I agree that bullet ogive inconsistency can affect COAL.
Im fairly new to reloading, but once I started seating to CBTO I discovered that my variation is limited to any flex in my press where the COAL has varied up to +/-.010".
I dont have a way to measure my bullets profile or ogive, but my wild guess is any variation is less than .005" at the most. I think for the purpose of the OPs question is if he measures to the CBTO then he wont get the variation in his jump to the lands which is what matters and his measurements will be consistent.

 

[judgebill]

Okay, I get it now. I'm seating bullet with a constant dimension between the shell holder and the bullet seating die. That distance is constant. What isn't necessarily constant is the location of the spot on the orgive of the bullet that I'm using to measure CBTO. If there is a variation between bullets that will give me the variation in CBTO. Yes, the differences are measured in .001 to .002 and to be honest, the rifle still shoots into 0.5 with 5 shots at 100 yards. Thanks guys for your wisdom and many suggestions.

 

[Rick Richard]

Okay, I get it now. I'm seating bullet with a constant dimension between the shell holder and the bullet seating die. That distance is constant. What isn't necessarily constant is the location of the spot on the orgive of the bullet that I'm using to measure CBTO. If there is a variation between bullets that will give me the variation in CBTO. Yes, the differences are measured in .001 to .002 and to be honest, the rifle still shoots into 0.5 with 5 shots at 100 yards. Thanks guys for your wisdom and many suggestions.

You got it now. Hammers are the closest being dimensionally equal from one bullet to the next followed by Berger in my opinion.

 

[Rhett Crider]

Okay, I get it now. I'm seating bullet with a constant dimension between the shell holder and the bullet seating die. That distance is constant. What isn't necessarily constant is the location of the spot on the orgive of the bullet that I'm using to measure CBTO. If there is a variation between bullets that will give me the variation in CBTO. Yes, the differences are measured in .001 to .002 and to be honest, the rifle still shoots into 0.5 with 5 shots at 100 yards. Thanks guys for your wisdom and many suggestions.

Correct. CBTO and COAL do not go hand in hand loading Tangent ogive vs. secant ogive. If you are loading the same bullets, lot number, not compressed, 0.001-3 neck tension, then there should not be any variance as long as your die is locked down. Any variance would be from the bullet ogive during mfg and should be very minimal. I use Redding micro seaters and all have been switched to VLD seater stems. Even w/ the VLD stem, I occasionally will get a Berger nose stick in the stem (bullet/die pops on retracting stroke from spring tension of case body) thus affecting both measurements. A little graphite on the bullet tip helps here.
BTW-Orkan's information is spot on. Worth the call if you have any questions.

 

[Justice1327]

Tolerance stacking...everything from your equipment, bullets, case, dies, to the amount of pressure and speed applied during your operation contributes to variations found in the finished product.

 

[FEENIX]

Tolerance stacking...everything from your equipment, bullets, case, dies, to the amount of pressure and speed applied during your operation contributes to variations found in the finished product.

^^^This!^^^

 

[GrayCreed]

This…if I push hard and fast it'll seat a lot deeper, my shoulders will also bump a lot more. Someone needs to make a press that'll stand up to increased pressure.

Also, I've noticed that when I bump shoulders the more lube I use the more it bumps back. I try to get consistent but it's tough to get them all the same.

Anybody else notice these things? I'm using an rcbs summit press.

That happens to me as well. I try not to lube the shoulder for that very reason, only lube the body, thats what gets stuck in the die anyway.

 

[BillLarson]

Because seating dies use the bullets ogive not the tip.
Measure yout CBTO distance and they will all be the same, compared to the COAL.

I find the COAL can vary up to .010" but my CBTO is within +/- .002"

Does,nt bullet length affect bullet weight...???