Sort by bearing length and by weight?

[Boss Hoss]

I don't remember saying anything about hammering it through. I believe the word I used was "pushed".

The point was that the extreme pressure curve and acceleration cannot be replicated so it makes no difference really.

 

[Edd]

... so it makes no difference really.

I don't agree. I think the bullet may go thru a reformation process that would put those sorted in .001" increments in different batches than they were in before passing thru the rifling.

 

[esshup]

Edd,

Food for thought. The bullet might get a swift enough kick in the butt so that it obturates deeper into the rifling than if just pushed thru, changing the bearing length vs. a pushed bullet.

Not 100% sure, but that might happen if the O.D. of the groove is larger than the OD of the bullet.

 

[Bart B]

For all you know, bullets sorted to match in bearing, or weight, won't match in BC.

A common occurance. There's one reason why a batch of bullets with identical weight, shape and outside/inside dimensions, they will not have the same BC. There's only one way to test them to find out which ones those are. And it's been done; with incredible results.

 

[Mikecr]

I agree that if ALL things match then so will BC.
But one parameter match, or even two(like weight and bearing), is not ALL.
Hell an opened meplat, would wreak havoc on assumptions that bullets are matching -based on bearing to base and weight.
And so would base diameter, base length, base angle, nose length, ogive radius, and bullet diameter.

It's a stretch to assume ALL these match, merely because one or two of them 'seem' to, and with the only basis being anecdotal shooting results rather than measures with any scientific method..
I suggest 'seem to', because the measurement methods here are not at all qualified measures, but abstract comparisons only. You aren't actually measuring bearing length, but comparing one unqualified measure to others.

For example, with a 6mm, 15cal secant ogive, a variance of 0.2 in ogive radius(from 15.0 to 14.8) would shift your buhay measurement datum(if .236) outward by .003" making it 'seem' as though your bearing is .003" longer.
But combined with ALL parameters mentioned, your bearing could actually be anything(longer or shorter).
Yet you would sort bullets on this alone?

To measure bearing length you would first qualify datums that are base angle, and ogive radius, so that bearing alone is isolated.
Then, MAYBE, very difficult testing might show an affect of bearing variance to MV.
Until then, it is merely mob murmuring..

 

[Bart B]

I agree that if ALL things match then so will BC.

What are all those things?

All I've seen listed in this thread are most of the external dimensions. There are at least two others inside; jacket wall thickness is one.

 

[Gene]

What are all those things?

All I've seen listed in this thread are most of the external dimensions. There are at least two others inside; jacket wall thickness is one.

Trim length consistency. Or maybe that is external.

 

[esshup]

To measure bearing length you would first qualify datums that are base angle, and ogive radius, so that bearing alone is isolated.
Then, MAYBE, very difficult testing might show an affect of bearing variance to MV.
Until then, it is merely mob murmuring..

Isn't that what the tool does? It's not measuring from the base of the bullet, nor the nose.......

 

[Mikecr]

There are at least two others inside; jacket wall thickness is one.

True Bart. There are a lot of things to consider before tossing bullets, -or keeping bullets, based on measure.
Jacket thickness and variance affects stability and would be compared with a Juenke ICC. Same with core depth, which can be checked with a special indicator anvil.
We could benefit from a tool for meplat measurement, which is tricky, and really a bunch of other things..

But I suspect that until we have this, most shooters will continue to generalize value beyond rational in what they have today..

esshup, the tool is often used both with and/or without it's base.
And yes it does measure from the nose. The indicator anvil rests on the nose.
With qualified base angle, ogive radius, and appropriate tool leade angles, the base would be used to compare bearing only(isolated).
Even this is not a 'measurement', without a standard for indicator zero.

 

[Boss Hoss]

day..

esshup, the tool is often used both with and/or without it's base.
And yes it does measure from the nose. The indicator anvil rests on the nose.

Your tool is dfferent than mine.

Bearing Surface Comparators

 

[esshup]

Bearing Surface Comparators

I have the same tool with the exception of using the stepped bottom piece on the dial indicator as well. There's a machined teflon sleeve that fits into the one that I use on the indicator, that is a snug fit to the indicator stem. There is a hole drilled thru it, and the stepped part is threaded.

I rotate mine a bit too to get it "seated", and use a round plastic headed thumbscrew instead of an allen head. But, basically that unit and mine is exactly the same in how it works, and how it measures.

 

[Mikecr]

Your tool is dfferent than mine

Same tool, nothin rare about em.

 

[Bart B]

Trim length consistency. Or maybe that is external.

I'd say it's external. Whatever it is, it will determine to some extent the meplat shape of a hollow point.

The other internal thing is balance. With perfect dimensions in jackets and cores before they're seated and the ogive formed, the core may not be perfectly uniform around the inside of the jacket. Maybe the lead's not perfectly homogenous; one side's heavier than the other.

A friend spun some 30 caliber match bullets that had been run through an optical comparator to ensure uniform outside dimensions. Spun at 30,000 rpm, the worst unbalanced ones flew out of the collet holding them. Best ones drew the least amount of current to the motor spinning the collet; evidence there was no unbalance to load the motor bearings up and require more current to spin it up to speed.

Those perfect bullets shot an inch or less at 600 yards; the others worse depending on how much unbalanced they were.

Bullet companies shooting bullets through chronographs and timers have observed that bullets leaving at the same speed have different BC's. That's caused by the slight unbalance bullets have; the more there is the more drag the bullet has so it's BC will be lower.

All of which, to me, means that measuring all the static properties of bullets then sorting them into "perfect" and lesser lots, those "perfect" ones will still have some degree of unbalance that'll cause small accuracy issues. So it's gonna be hard to differentiate between what causes inaccuracy, slight unbalance or mechanically measured differences.

 

[Mikecr]

I was coaxed into sale of my Juenke..
Maybe some day I'll take on the challenge of building a bullet spinner of sorts.
Something similar to Vaughn's pneumatic, or maybe like your purely electrical.

I agree that imbalance, and poor release from the muzzle, are very real factors.
We can manage crown quality and reduce muzzle pressures with cartridge design and load/barrel length/twist choices. But a wacky bullet is still bad news.