Folks:

I've been using a comparator to measure the over all distance to the lands for several different bullet weights and manufactures, and need to check my findings with those who have a lot more experience at this than I do. So here's a quick question: All of the lengths for ogive touching the lands has been the same for 140, 150, and 160-grain Partitions. Does that sound right? I know it will vary from manufacturer to manufacture, but within manufacturer and bullet style, do the ogives measure the same regardless of the bullet weight? I'm just trying to make sure that there isn't something screwy with my measuring technique.

Thanks.

RM

Using the comparator is getting pretty picky about your handloads - but that is ok. Rev, I found out that bullets of different weights do NOT have the same distance to the rifling - when using the comparator. But if they did it would be just a coincidence. In fact, a box of lead tipped bullets of any style or brand will have differences in OAL's due to damage to the tips. But we know that the tips do not contact the lands and grooves. A comparator here would be a better measuring tool.

My biggest revelation came when using a comparator for 150 gr Partitions for a .270 Win. with a cannelure. When I laid out some 150's without a cannelure they looked slightly different. Wondering if there was an optical illusion, I put them to the comparator test and they measured differently.
The cannelured bullet contacted rifling sooner than the more slender bullet without a cannelure.

Recall that Mule Deer sometimes writes that manufacturer A or B changed something about the bullet design or hardness but never make it publically known. That too would certainly play into your contact point and only the comparator would pick up on that. Its a handy tool.

Thanks for the comments.

Yes, using a comparator is getting a bit picky, but there's a reason: I have a cranky Featherweight that I'm going to force into submission, and I'm working on getting any edge I can. I figure consistent loading depth can only help.

I have a new caliper coming today, so I'll see if that makes any difference. When I was looking at 140, 150, and 160-grain Partitions, and the numbers were coming out the same, I figured it had to be one of two things: either the dial on the caliper is too hard to read (retired CPAs generally have lousy eyes) or the ogives are the same and the weight differences are all in the shank. The new caliper has a digital display, so I'll run the test again this evening and see how things turn out.

Thank again for your observations. It's helpful.

RM

If the 140, 150 and 160 had the same comparator measurement, what were their OAL's?

I didn't quite get that far, but netting out the comparator would put it at 2.5795 inches from base to ogive on each round since they all measured 3.5850 with the comparator (comparator length is 1.0055 inches). I didn't measure how much of the base of the bullet is in the neck, but I expect the OAL will be shorter on the 140-grain loads if I'm going to have at least .284 in it.

I should add that even tipped bullets like the Accubond can vary in the length of the bullet. Those white tips aren't always identical. All this points to the comparator as the best way to get consistent COAL's.

It's rare that this happens so don't count on it. Even among supposedly identical bullets they'll vary by lots. I initially worked up a load with 105 Amaxs for my 6 BR years ago and wrote down the cartridge OAL and my comparator reading at that OAL. When hornady closed out the Amaxs I bought a thousand. I pulled out some of the newer ones the other day and loaded to my desired COAL then checked it with the comparator, it was off by .025". The different lots of bullets were considerably different in their ogive placement even though they were the "same" bullets.

The moral of the story is always check!

That's one reason that I like to buy enough bullets, powder, brass, or primers to last a while. I don't like re-working loads to deal with inconsistencies between different lots.

Update:

I picked up a new iGaging Origin (digital), attached the comparator, and zeroed it out. Here are the averages of five measurements, from base to where the ojive meets the lands in a BACO Featherweight 7x57:

Nosler 140-grain Partition: 2.5755"
Nosler 150-grain Partition: 2.5770"
Nosler 160-grain Partition: 2.5785"

From this it looks like the OAL distance, from base to lands, using the ogive as the measuring point, changes .0015 inches between each successive weight. This will be helpful when working up a load for this particular rifle. A couple of my others aren't so picky, but this one seems to be.

BTW, I know JB and others have said Partitions really like a kick in the pants as far as accuracy is concerned, but for those who use them, what have you found with regards to the jump. Close to the lands? Or do they like a little jump?

Thanks for your patience.

RM

Don't measure to the fourth decimal point or you will drive yourself batty.

Nuzzler is easily amongst THE schittiest in QC "control".

Hint..............

Yeah, it didn't take long to figure that out. I also found that if I wanted to get a couple of different readings, all I had to do was spin the bullet in the comparator. That's why I took an average of several measurements. But at least it's going to give me a baseline from which to start.

So far, in measuring several different brands, Sierra has been the most consistent, but I'm not planning to hunt with them...at least not at this point.

If you have a factory box of 7x57, or whatever other cartridge, it would be interesting to see how uniform they are. This is important but we can't get carried away with the minutia as other factors are in play too.

Bedding good? Both bolt lugs making good contact? Good crown? Assembled cartridges straight?

Factory loaded Partitions? Unfortunately no.

Factory bedded and crown is good. Bolt lugs, I don't know. Sharpie test?

As for cartridges, both factory and handloads shoot the same. Handloads are Redding body die, Lee collet, and either Lee or Redding seating die. I don't have a runout gauge, but they pass the "roll test."

When the weather cooperates I'm going to load some 160-grain Sierra Tipped Match Kings and see how they do. My MRC likes just about anything in the 150- to 160-grain class, so hopefully I can get this one to shoot too.

Mathman:

Pretty evenly worn, so I'm not sure what's up. Of the three 7x57s I generally use, two shoot sub 1 inch groups at 100 yards, albeit with heavier bullets (154+ grains). This one is proving to be a bit erratic, generally shooting 1.5 inches or so, and that's with a proven scope, so I know it's not the glass.

RM

What is wrong with 1.5" or so accuracy?

Nothing really. If that's the best it'll do then that's the best it'll do. But I'm going to find out if there's more in there to be had. I have a bunch of different bullets and several different powders, so I'm going to wring it out and find out for sure.

Ok.

Good luck,Rev.

Besides, in this day and age I think we expect more. Maybe that's unreasonable and we've just been spoiled, but I think our expectations have changed as well.

Thanks. We'll see what happens. It's not like it's the only one I have.

A 1.5" group will suffice for a lot of big game hunting. For varmints,not so much.

I'll trade you,your 7x57 load developing for my .460 Wby load developing.

We'd be settling for a 12 inch "group"!

Rev,put enough lead in the air you're bound to hit something.

Rev - for starters, are the measurements above for cartridges seated to touch the lands?
If you're measuring the bullet ogive at the same place it contacts the lands (especially among similar bullet nose profiles), then of course the loaded cartridge base to ogive length will be similar for all of them, because they're all matched to the same fixed distance (the rifle's chamber). Finding one that varied a lot from the others would be cause to investigate why.

If you're loading them to the same OAL and then finding similar base to ogive (BTO) measurements, that's a different thing that would indicate the bullet noses are similar length and profile. To check, measure the tip to ogive (TTO) distance for each of those three bullets; that's what affects distance to the lands compared to OAL between different bullets. If those three bullets have similar TTO measurements, it means by some coincidence that family of bullets probably uses similar or even identical nose profiles.

Good post.

Much appreciated.

Thanks



From base to touching the lands, shouldn't they all be the same length regardless of bullet weight and design?

RM

I would work up loads with the Sierras to establish base line accuracy. Hate to admit agreeing with stick but you could drive yourself nuts trying to get the best accuracy from partitions. I do like the bullets but quit anytime I am close to or under and inch. Far cheaper and easier to get accuracy with the Sierras. Also a faster powder has turned things around for me with Partitions, I think JB recommended this or even the Nosler staff. Like most 100 year old cartridges the chamber dimensions vary greatly. Even with the similar ogive profile it will likely have wildly different seating depths for the different rifles. Good Luck.

BWA guys may help here. Ask for HOOK here. He might be able to help you. Be Well. Rusty

Excuse my ignorance but explain BWA.

That is the plan. I have several different powders to try, beginning with the old standby, 4350. Once I get a baseline - if I get a baseline - I'll go to work with some different powders and bullets and try to put together some hunting loads.