OAL vs. Comparator; What difference does it make?

[berettaprofessor]

I see a lot of posts about relying on a bullet comparator to compare bullet length versus measuring OAL. Today, I was loading up a three different bullets for a comparison accuracy trial of 224 Valkyrie and I thought, what the heck, this is a perfect chance to measure these both ways (direct OAL or with a Hornady Bullet Comparator) and compare the consistency.

Specifics: All bullets were seated with an unaltered Lee 224 Valkyrie seating die. I set the first bullet OAL to 2.260 and did not readjust the OAL while I loaded 5 each of three different bullets. Cases had been trimmed to 1.590 and deburred after neck sizing in a Redding die. The Hornady Comparator test used the 22 gauge insert to measure base to ogive in an analog caliper. The OAL base to tip length was measured with the same analog caliper. Results in the table below:



Obviously, the most important lines are the spread and SD. As measured OAL with the caliper, the spread between minimum and maximum of the 5 bullets of each type varied from 0.006 to 0.002. With the Hornady Comparator, the spread was exactly 0.002 for all bullets; which, I would conclude, is the repeatability of seating each of these bullets with a standard Lee seating die combined with the variation induced by my measurement with the comparator and caliper and the variation of the bullet shape itself. Pretty darned consistent either way, but now I wonder if consistency would be better if I used a micrometer adjustable die from another manufacturer (I don't have any). Would "0.000" versus "0.002" spread base to ogive really make a measurable difference with all the other variables that might affect long range accuracy?

Conclusion: Yes, the Hornady bullet comparator is better at demonstrating length consistency in loaded rounds. Is it worth the extra cost and time to confirm that seating dies are consistent? That's up to each of you, but myself, I'm probably not going to spend a lot of time measuring other than OAL. I don't shoot good enough to worry about the difference, at least yet, and maybe never.

 

[Walkalong]

When it comes to fine accuracy how far the bullet ogive is from the base of the round, and how far from the ogive to the rifling are both very useful things to know. They will also vary very little, vs OAL, which can easily have a .010 spread.

Lots of rifle loading doesn't need to know anything about the ogive, so some would say that is a waste of time and OAL is more important to them. It gives us something to compare the load data we use with, and it makes sure things fit the gun, so it is useful.

 

[Rule3]

And this is where folks will enter and say you do need one of hose more expensive seating dies
Don't forget to weigh each bullet and get a concentric gauge as well

 

[edwardware]

Many finely manufactured bullets (Sierra, Hornady, etc) exhibit a surprisingly large variation in tip-to-ogive or -base, especially HPs. Since ogive and base locations are much more critical to accuracy than tip, you should measure ogive.

But, unless you're already tuning seating depth by 0.010, tip reference is probably sufficient.

 

[taliv]

In case it’s not obvious, the traditional mfg process for making match bullets (which are usually open tip or OTM) means the base is super consistent but the tip looks like a jagged mountain range. the tips can cause the length of the bullet to vary by 5 thou or more even when the ogive to base varies by well under a thou.

You want your seating depth to vary by less than a thou. Thus, if you are measuring to make sure you do in fact have an acceptable consistency in seating depth, you must measure from the ogive because measuring oal is going to show 10x as much deviation as you’re hoping for and how could you know where it’s coming from?

Also
When you’re trying to figure out how far off the lands you are, 6 thou is a lot.

 

[taliv]

That said, I’d expect bullets like the hornady a tips to show a fairly consistent oal.

 

[Walkalong]

Their 6MM 108 Gr ELDs are pretty good there.

 

[JFrank]

In my discipline, seating is King..
Notice below the four depth pictured and how dramatically different each test group prints on paper at 300 yards. My window is between.015 & .020 off the lands / riflings , any closer they will stand up any further away they become to wide and erratic. I stay at .018
I only measure bullet base to ogive selecting to load those within .001 each session.
It doesn’t take anymore time then weight or measuring OAL but your target will definitely know the difference.
J