Bullet Length Variances

[BamaAl]

Today, out of curiosity, I measured my SMK 175s as I was reloading. It was the first time I've ever checked and I expected 2 or 3 thousandths delta. When everything was done I was surprised to find they varied up to 8 thouandths over about 30 rounds.

So now I'm curious. Just how much difference can that make at 600-1000 yards? It sounds insignificant but every time I think that I find out I'm wrong.

Also, how does a meplat trimmer work? Does it just point the bullet or is it like a case trimmer and trims the bullets to the same length?

Frankly I'm not good enough that it would make a huge difference to me. It's not like I'm worried about an X vs. a 10 yet. I'm more worrie about dropping a 10 to a 7.

 

[Helmet]

Re: Bullet Length Variances

I'm curious about this also. This is the main reason why I still haven't used SMKs. Goofy looking tips.

 

[Helmet]

Re: Bullet Length Variances

That sucks. I guess I'll just stick with Hornady.

 

[boltgunluvr]

Re: Bullet Length Variances

Sierra, Hornady, Berger, Speer, etc...dont be fooled, they all have variances. They are all great quality. Just find what works for your rifle. If one is looking for the perfect bullet, then one will need to turn them on a lathe and guess what...they'll still have variances.

 

[Gene Poole]

Re: Bullet Length Variances

Hornady A-Max have a lot more variance lot-to-lot than SMKs in my testing. I get average differences on the order of 0.008 on the base to ogive measurement and 0.011 base to tip on the A-Max and about 0.003 and 0.006 respectively for the SMKs. This was done on 4 lots of 178 A-Max and 3 lots of 175 SMK using the Hornady comparator.

I try to seat to a consistent ogive depth and ignore COAL but I'm not sure if that should be adjusted to the difference in base to ogive or not. According some sources, it is the timing of the bullet's base exiting from the muzzle that affects accuracy; another source(1) says that it is bearing surface of the bullet interacting with a critical zone in the barrel's harmonic cycle that is most responsible. I don't have enough data to make a conclusion on this though.

1. Shock Wave Theory – Rifle Internal Ballistics, Longitudinal Shock Waves, and Shot Dispersion , Chris Long [2003]

 

[ksthomas]

Re: Bullet Length Variances

BamaAl,

It makes absolutely no difference at all. The variation you see are in the total legnth of the bullet, which means absolutely nothing. You're seating off the ogive, not the tip, which renders these differences moot. If you've got rounds that are varying in the ogive measurement, <span style="text-decoration: underline">then</span> you've got problems.

As for these bullets being made on different machines and mixed together, that's totally false. They come off one machine, and from the same forming die. If soemthing happens to cause that die to be replaced, that starts a new lot #. If there's another batch of jackets that replace the one that's currently being used, that's a new lot #. If there's any major change or adjustment to the presses during a run, that's a new lot#. Actually, it's very rare that a single lot encompasses more than about 30,000 of these bullets. They are never mixed, and are certainly never assigned a lot number after the fact. I don't know of a single one of any of the major makers that does this.

 

[BamaAl]

Re: Bullet Length Variances

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Kevin Thomas</div><div class="ubbcode-body">BamaAl,

It makes absolutely no difference at all. The variation you see are in the total legnth of the bullet, which means absolutely nothing. You're seating off the ogive, not the tip, which renders these differences moot. If you've got rounds that are varying in the ogive measurement, <span style="text-decoration: underline">then</span> you've got problems.

As for these bullets being made on different machines and mixed together, that's totally false. They come off one machine, and from the same forming die. If soemthing happens to cause that die to be replaced, that starts a new lot #. If there's another batch of jackets that replace the one that's currently being used, that's a new lot #. If there's any major change or adjustment to the presses during a run, that's a new lot#. Actually, it's very rare that a single lot encompasses more than about 30,000 of these bullets. They are never mixed, and are certainly never assigned a lot number after the fact. I don't know of a single one of any of the major makers that does this. </div></div>

Thanks Kevin. That's what I thought. And as it happens I just got a Hornady comparator and OAL guage in the mail today. And I do not like what the measurements are telling me at all. About to post a new topic to ask some questions.

 

[Helmet]

Re: Bullet Length Variances

It might not affect the bullet jump, but SMK tips still look goofed up to me. I'm not saying that the Hornady tips are perfect, but they look much better to me. At least the ones I'm using. I measure to the ogive so I don't care so much about the randomly shaped tips effecting the oal, but I wonder how much it effects their flight.

 

[Greg Langelius *]

Re: Bullet Length Variances

Thank you Kevin.

This type of question has come up a lot recently.

My opinion is that factory QC specs are biased in the shooter's favor, and that the kind of precision needed to meet the degree of perfection some folks demand would make the cost of the resulting product prohibitive.

A decade or so ago, there was an article in a well respected shooters' magazine where bullets were deliberately deformed, loaded, and fired for accuracy. The amont of deformation needed before any noticeable accuracy degradation crept in was pretty astounding. This leads me to believe that QC specs are at least as much about cosmetic appearance as they are about accuracy.

IMHO, it's too easy to blame the implements. I know darned well that when I miss, it's not the components (or 'de debbil') who made me do it.

Greg

 

[ksthomas]

Re: Bullet Length Variances

No problem at all, and glad to help. The issue of length variation is a big one, mostly because it's so easy to measure. And yes, they do vary. It really doesn't make any difference though, so long as the critical leade/ogive relationship remains constant. That's a lot more important, but until fairly recently, wasn't a measurment shooters really paid much attention to. Eintstein once said that "not everything that can be measured, is important, and not all that's important can be measured." This is one of those examples.

As for the tips, again, it's a highly visible part of the bullet, and it's the first thing that people tend to focus on. It's also probably the least important area of the bullet where accuracy is concerned. It can cause some variation in BC measurements, but there's also a ton of other variables that do as well. From an accuracy standpoint, however, it's irrelevant. Think of it this way; when you look at a bullet point on, the tip is at the very center of that bullet. Almost anything that causes inaccuracy is on some level dependant on where it's located within that bullet. Those imperfections that are farthest outward (like concetricity issues at the bearing surface, for example) are the ones that have the greatest influence. Imagine a void, an actual air bubble, inside the lead core of a finished bullet. If that void where located exactly, precisely at the center of axis of that bullet, it would have literally no effect on that bullet's accuracy. Now, move that same void out to one side, just under the jacket on one side of the bullet, and you create an offset between the axis and the center of gravity. NOW you've created an accuracy issue that will show up quite plainly on target. Nothing too difficult to understand, but I've rarely heard shooters mention it in these discussions. Anyway, I hope that helps put some folks minds a bit more at ease.

 

[Helmet]

Re: Bullet Length Variances

Thanks Kevin. I think I'll give the 7mm 175 SMKs a try.