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Old July 5, 2012, 11:37 AM   #1
ThisIsMySig
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Differing Bullet Lengths

I have bullets from three different manufacturers. I decided to measure the length of 10 from each maker. Here are the results:
  • .45 cal 200 grain LSWC ranged from .642 to .650
  • .45 cal 200 grain CPRN ranged from .566 to .569
  • 9mm 124 grain CPRN ranged from .581 to .584

I would guess that this is common amongst manufacturers, however, assuming of course that all the bullets are seated to the same depth, the differences in bullet length would appear to cause differences in case pressures.

In the case of the LSWC, there is a range of .008 thousandths. That's quite a difference and might explain why I am getting different results from the same load. An example of that difference is one spent case properly ejecting and one stove piping.

What do you guys think?
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Old July 5, 2012, 12:25 PM   #2
g.willikers
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That's why the load data show different loads for each and every bullet design, weight with variances.
Although the differences in your swc are probably not the cause of such differences in ejection patterns.
Just guessing, it's more likely either an erratic powder drop or a problem with the gun.
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Old July 5, 2012, 12:32 PM   #3
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g.willikers, he's talking about manufacturing variations for a specific bullet. Unfortunately, no load book is going to be able to account for that. My buddy tried to load some .264 Berger VLDs one time for his 1000yd rifle and found that while they all weighed right at 130grns, the variation in lengths were so bad that he just gave up on them. You could line them all up and see the variation with your eyes. Needless to say, Berger VLDs are off the shopping list now.
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Old July 5, 2012, 12:39 PM   #4
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Yeah, there's better quality from some manufacturers than others.
And it's not only on the outside that quality can suffer.
Like small air pockets from the casting process that cause erratic flight.
Having measured the 200 grain swc I mostly use, there's not much difference in bullet length from batch to batch.
The measured difference could be caused by slight irregularities in the casting surface, rather than in the actual bullet length, too.
So the difference the OP found might not be actual.
Just a thought.
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Old July 6, 2012, 04:47 PM   #5
ThisIsMySig
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The differences I measured in bullet length are actually, well, actual. That's why I measured 10 of each.

So the question remains: Assuming a difference of even .003, would this be enough to appreciably raise case pressure and affect performance?
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Old July 6, 2012, 08:19 PM   #6
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In a pistol bullet I don't think it is enough of a difference that anyone would ever notice outside of some type of scientific measurement. Where it comes into play is on a long range rifle where that slight pressure difference translates into a much larger group.
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Old July 7, 2012, 10:05 AM   #7
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Using QuickLOAD

I calculated pressure changes for a 0.003" increase in seating depth for two powders under a 200 gr lead FN bullet in the .45 ACP cartridge, starting at 21,000 psi ("+P" pressure limit for .45 ACP). For the faster powder I got a 70 psi increase, and for the slower powder, I got a 182 psi increase. (I was expecting the opposite for the increases, but who am I to argue with QuickLOAD.)

Anyway, I think this showes that the bullet length variations that you measured are inconsequential. Variations of a few thousand psi from shot-to-shot are typical on pressure measuring systems with good quality ammo.

Also, keep in mind that sprue marks on the bases of cast bullets can affect length measurements by a greater percertage than the actual percent change in the volume of the bullet inside the case. A 0.003" ridge or bump on the bullet base is usually inconsequential to accuracy as well as to pressure.

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Old July 7, 2012, 05:53 PM   #8
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SL1: You have certainly answered my question about seating depth. Perhaps the 182 psi increase is due to that fact that the slower powder has more time to build pressure before pushing the bullet out.

It's great information and I appreciate your taking the time to do those calculations.
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Old July 7, 2012, 06:20 PM   #9
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It's due to the amount of empty space left in the case being smaller. The space between grains of powder is less than empty space, obviously. So when you start with the case more full of powder, as will be the case with most slower loads, you are starting with less total empty space under the bullet. Thus any given change in seating depth results in a larger percentage of the empty space being changed in a slow powder load.

The lengths of your bullets are pretty normal. The trick is to seat from the ogive, which is more consistent, to get the base of the bullet the same distance from the head on the inside so the powder space is about the same. Then let the COL vary slightly. If you look at military and commercial hardball, for example, even though the spec allows for 1.275" COL, you find most of those using the military style elliptical nose profile will actually vary from about 1.260"-1.270" COL. All within the upper limit for magazines and not enough difference to matter to feeding. Those with a more hemispherical nose profile will be seated to an even shorter COL.

The match rifle bullets by Berger have some of the best mass symmetry money can buy, which is why they shoot so well. The differences in length on hollow point match rifle bullets is almost all due to the hollow points not drawing to exactly uniform meplats. Some tilt across the hollow points from one side to the other is pretty normal, but that doesn't affect the ogive distance off the lands, nor the ogive distance from the base, which matter more to accuracy. If you actually have a feed problem because of hollow point irregularity, you can get both a meplat uniforming cutter and a pointing die and first cut to tip back a few thousandths to get uniform length and diameter, then return it to a point in the pointing die to retain BC. More bother, but lots of things are in the precision shooting game.
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Old July 7, 2012, 07:01 PM   #10
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I expected some variation in bullets lengths but not .008 as was the case in one of the samples. This lead me to wonder if that variance affected pressures. It does, but as SL1 pointed out, not enough about which to worry.

Yes, seating from the ogive was my thought as well. Doing so would negate any irregularities in the curved portion of the bullet. I am using LSWCs. Of course the seating die is designed for a round nose bullet. I get fairly consistent COLs if I seat carefully. Another way to seat from the ogive on this type of bullet would be to measure the distance from the bullet shoulder to the case head. This however, adds considerable time to hand loading. Although the dome shaped seat in the die handles the SWCs fairly well, ideally, a seating die specifically designed for LSWCs would be the best.
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Old July 8, 2012, 02:30 AM   #11
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Yes. I turn SWC seaters on my lathe if I don't have a match available. I avoid the RN seater profiles for SWC's because they allow more bullet tipping.

The last time I went through a lot of Sierra MatchKings, I had 0.007" length variation due to the hollow point irregularity. So your .008" is not unusual.
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Last edited by Unclenick; July 8, 2012 at 10:56 PM. Reason: typo fix
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Old July 8, 2012, 09:14 AM   #12
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small question

What is the variance in your measuring tool?
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Old July 8, 2012, 10:35 PM   #13
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Its not going to matter at handgun distances unless you're shooting for big money in which case you'd be running better bullets anyway.
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Old July 8, 2012, 10:44 PM   #14
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WESHOOT2 brings up a good point. If you are using junk calipers, who knows what the actual numbers are.

At handgun distances, .008" bullet length isn't worth a second thought.



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