Reloading Issue: Why do measurements vary?

[judgebill]

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"

 

[orkan]

Incorrect treatment during the tumbling process or sizing process... is the number one culprit of this. Variation on internal neck surface shows its face during bullet seating.


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[judgebill]

Incorrect treatment during the tumbling process or sizing process... is the number one culprit of this. Variation on internal neck surface shows its face during bullet seating.


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BUT, the one "constant" is the distance between the shell holder and the seating die. Even the cartridge case is shorter or longer, the bullet is shorter or longer, shouldn't the constant dimension of how far into the case the bullet is seated be consistent? A shorter bullet won't go as far into the case, a longer case will have the bullet seated deeper. At least it so occurs to me.

 

[orkan]

How much force is on something... determines how much it moves. If the force varies, so too does the final dimension. This stuff isn't rigid in the sense you're speaking about. It moves, and springs back when force is removed. Its fluid, based on the control of the rest of the variables.

More seating force, means the ogive of the bullet deforms more. The neck is compressed more. Less, means less... that means the uniformity of the interface surfaces, has a say in how it works.


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[Varmint Hunter]

The BIGGEST factor causing varied seating length (cbto) is powder compression. At least IMO. There are many other factors, but powder compression has always resulted in poor CBTO consistency for me. Generally, I avoid powder compression but sometimes it's just not possible.

I'd add to that, if the pressure to seat each bullet feels different (some tighter and some looser than average) than you can bet the CBTO will vary. There may be some spring back of the neck as the bullet seating force is released but I'm not sure about that.

 

[Huntsman66]

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…

 

[Carlos88]

Assuming no powder compression, base to ogive length and bullet oal differences by the thousands of an inch, etc. will cause slight variations. Ultimately accuracy with satisfactory velocity is what matters. The rest is a hair pulling exercise. I know this because I've got few left and getting worse everyday. Either that or my hat is pinching the blood off to my hairs.

 

[Ucsdryder]

How much force is on something... determines how much it moves. If the force varies, so too does the final dimension. This stuff isn't rigid in the sense you're speaking about. It moves, and springs back when force is removed. Its fluid, based on the control of the rest of the variables.

More seating force, means the ogive of the bullet deforms more. The neck is compressed more. Less, means less... that means the uniformity of the interface surfaces, has a say in how it works.


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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.

 

[vancewalker007]

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"

The parts involved all vary slightly ie. neck tension, brass hardness, bullet ogive points relative to their base, brass neck length, speed the persons arm moves the ram. All these things add up to the slight variations you are speaking of. The more accuracte you can make all these things then the more accurate the end product is. For example, you could sort bullets by their ogive to base lengths. You could very carefully cut your cases to within say .001-.002in.

 

[RidgeTop]

The parts involved all vary slightly ie. neck tension, brass hardness, bullet ogive points relative to their base, brass neck length, speed the persons arm moves the ram. All these things add up to the slight variations you are speaking of. The more accuracte you can make all these things then the more accurate the end product is. For example, you could sort bullets by their ogive to base lengths. You could very carefully cut your cases to within say .001-.002in.

I sort bullets to 5 weights with weights to the .001 of a grain. You would be surprised how much wt. varries even in the same box. Some time a + or - 1.5 gr variance. Jim

 

[vancewalker007]

I sort bullets to 5 weights with weights to the .001 of a grain. You would be surprised how much wt. varries even in the same box. Some time a + or - 1.5 gr variance. Jim

Yeah, bullet weight can really vary, especially in the bonded bullet area. Try measuring the ogive to base lengths on some of those bonded bullets. They really vary. The monos and Bergers are usually very close in weight. I used to sort bullets, but I did a few tests with widely varying bullet weights and didn't find enough proof to keep doing it. Plus, I mostly shoot Bergers now and their weights are almost always right on.

 

[pdog shooter]

Inconsistent neck tension and carbon in the neck are my problems. The first I reduce with a mandrel and the second with bore brush and kroil. I figure that both will cause inconsistent seating force and the shoulder will give and spring back just a little. Also bullets are pretty good but the aint perfect. That's my theory.

 

[judgebill]

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.

 

[RidgeTop]

Inconsistent neck tension and carbon in the neck are my problems. The first I reduce with a mandrel and the second with bore brush and kroil. I figure that both will cause inconsistent seating force and the shoulder will give and spring back just a little. Also bullets are pretty good but the aint perfect. That's my theory.

I use SS rods and Dove soap and tumble. This cleans everything, including primer pockets.