Testing & Tuning & Tooling & More – Bullet tip measuring

[Ahhnother8]

Made and have been using this tool (exploded view) to measure just the tips of the bullets. It contacts at .183” diameter on the ogive, which is the same location that the Hoover trimmer bears. I believe that the newest Hoover trimmer bodies can also be used much like this tool. The dial indicator may need a longer than normal stem though.

By measuring only the tip, any other bullet dimensional variations are irrelevant. It makes it easy to determine exactly how much to trim the bullets to get a 100% cut on the circumference of each bullet. It is also surprising how often the bullets are not trimmed to a consistent tip measurement, due to not letting the cutter “dwell” for a moment. A thrust bearing between the trimmer body and the cutter stop collar helps a bunch. Without taking this measurement, one would never know that this error existed.

If pointing bullets, it is also useful to know how much the bullet tip is growing, due to the pointing. Yes, one can determine that same thing by measuring a given bullet before and after pointing, but it can vary somewhat by any tolerances in the sorting and by not chasing the overall length with the pointing die setting.

I also made inserts and a custom indicator tip to measure the actual length of the ogive, from the .183” contact point to just above the major diameter of whatever caliber is being measured.

Does any of this really matter? Been done before? Just food for thought, and your mileage may vary.

 

[ern.santos]

There's been enough internet and YouTube chatter how base to ogive measurement doesn't matter. I forgot which of Cortina's podcasts where Bob Bock's name was dropped, but it was mentioned that base to tip was the measurement that mattered.

Been done before? probably not that specific tooling. But it seems there's a convergence of sorts going on. If you've been using it since at least October, it seems to be working well enough.

 

[BoydAllen]

Have you seen much variance in what you refer to as the length of the ogive, within a box of bullets?

 

[Ahhnother8]

Have you seen much variance in what you refer to as the length of the ogive, within a box of bullets?

Short answer: No.

I saw a few tenths of variation, but I would attribute that to the measuring error in contacting two angled surfaces. Logically, the bullets all go into the same pointing die, so they should all be identical coming out. Excepting of course the very tips. A variance could occur if bullets came out of two different "identical" dies on two different machines and ended up in the same box. The bullets are all of such high quality that I cannot fathom that the bullet makers would ever allow that to happen. I don't even bother measuring the ogive any more, but now I know...

 

[CNC-Dude]

Yes, it was two podcasts with Erik Cortina, one with Bob Bock and another with Brian Litz where it was discussed by both of them that on OTM style bullets, the overall length matters much more than BTO for vertical dispersion at longer distances if longer projectiles are mixed with shorter projectiles in the same string of fire.

 

[Ned Ludd]

The critical distance for maintaining consistent seating depth is the distance between where the seating die stem contacts and "pushes" the bullet ogive during the seating process, and the point at which the caliper insert contacts the ogive when we measure cartridge base-to-ogive (CBTO, see image below). In my hands measuring numerous different types of Berger bullets, the base-to-ogive variance has actually been quite small relative to the nose length variance. I sort bullets by OAL prior to pointing, using length groups that cover .0015" in actual bullet length, which effectively translates to .002" between length groups (i.e. 1.5000" to 1.5015", 1.5020" to 1.5035", 1.5040" to 1.5055", etc.). Because BTO variance in the Berger bullets I have been using is so small, I believe that sorting bullets by OAL is effectively about the same as sorting by nose length, and thus also has the additional effect of generating more uniform seating depth by keeping the distance between the two critical contact points more consistant.



Bob Green makes a Comparator tool that allows one to sort bullets based on the distance between the critical contact points. I think it is a little different than the tool pictured above, but I'm not getting exactly how the OP's tool works solely from looking at the picture, so they might be the same/similar:

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