OAL Measurement

[RSAPD]

Just posting what I recently learned and for the experts here, feel free to chime in and correct me. I was trying to understand why my OALs were different per bullet I was seating. I asked the question and people replied with issues surrounding problems with the dies/equipment/brand, etc. I did not specify I was measuring from base to bullet tip nor did anyone ask. I had been wanting to buy a Hornady OAL gauge, so I started reading about how it works and I learned that measuring from base of the case to bullet tip can give variations up to .025, so the most consistent measurement is from the ogive. I had no idea. So i learned not only do I need the OAL gauge but also the the bullet comparator to measure from the ogive. Now I'll really know where the ogive is from the lands as I load. This was all news to me and though maybe sharing my experience might help someone. I guess I just assumed that high quality and match grade bullets were all consistent but they are not past the ogive.

[Winger Ed.]

I figure you're working on rifle ammo OAL.

Your measurements of OAL from the tip will pretty much always vary a little.
(especially on bullets with a exposed Lead tip because they get dinged around in transport and manufacture)

Since your seating dies 'grip' below the tip, as does the rifling in the chamber,
that little bit of difference in base to tip length doesn't really hurt.

If you really, really want to eliminate a more important variable-- segregate your bullets by a tiny amount of their weights.

[HWooldridge]

I’m the quality manager for a large production machine shop and am involved in measuring things on a daily basis. If I was interested in validating loaded shell length, I would use a ring gage that stopped at some arbitrary point on the ogive (a datum), and use a height indicator over a small surface plate to determine OAL. The remaining distance from your artificial datum to the tip won’t make much difference.

As an aside, we also make steel cores for a major component manufacturer in the US and the primary spec limits they want us to control from part-to-part are the largest outer diameter and weight. Ogive shape, length, angles, etc. all have fairly wide tolerances.

[M-Tecs]

https://bulletin.accurateshooter.com/2021/08/cartridge-base-to-ogive-cbto-length-factors-to-consider/

https://bergerbullets.com/effects-of-cartridge-over-all-length-coal-and-cartridge-base-to-ogive-cbto-part-2/

https://bergerbullets.com/shoot-better/shooting-knowledge/measuring-coal-and-cbto/

https://larrywillis.com/OAL.html

[jetinteriorguy]

One other variable for OAL and even measuring from base to datum, if your reloading shell cases that have been shot in a semi auto rifle sometimes the base can get knocked out of whack from the violent extraction. You should see what my AK does to brass rims.

[Finster101]

M-Tecs thanks for those excellent links.

[Hannibal]

I would add that if your bullet seater is contacting the tip of the bullet, you'll be chasing your tail trying to get your die set for a consistent length. Even when using a comparator to measure with.

[RSAPD]

Thanks for all the replies and passing on the links. Great info. Agree with cases from semi-auto. My M1 Garand can make the cases look like they had been in a major knife fight. I did take out my seating stems to make sure the tips were not contacting the stem because I thought the same thing about chasing my tail.

[ioon44]

Some really good info here, should be a sticky.

[Hdskip]

I’m the quality manager for a large production machine shop and am involved in measuring things on a daily basis. If I was interested in validating loaded shell length, I would use a ring gage that stopped at some arbitrary point on the ogive (a datum), and use a height indicator over a small surface plate to determine OAL. The remaining distance from your artificial datum to the tip won’t make much difference.

As an aside, we also make steel cores for a major component manufacturer in the US and the primary spec limits they want us to control from part-to-part are the largest outer diameter and weight. Ogive shape, length, angles, etc. all have fairly wide tolerances.

I use this gauge to compare shoulder length but could adapt it to do the same by locating on the ogive of a loaded round.


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