OAL vs. COL

[platoonDaddy]

Confused by OAL vs COL

Page 340 Lyman Reloading Book 49th Edition has a picture of a 9x19 cartridge with total length of 1.169".

On page 341 for 115gr Jacketed HP OAL at 1.090"

Hodgdon Reloading Data Center for 115gr JHP COL at 1.169"

My research on the terms:
OAL overall cartridge length
COL cartridge overall length

Are they not the same?

Assuming those two terms are the same, why the difference between Lyman vs Hodgdon for total length for 115gr JHP?

[5pins]

The difference in OAL is because of the bullets. A hollowpoint is going to be shorter then a FMJ. Also the bullet is going to be different from one manufacture to another. Some will have a shorter more truncated ogive then others.

[SteadyUp]

OAL and COL are the same thing. Just a different way of saying it.

[NWPilgrim]

The acronyms mean the same thing, overall length of the cartridge, but you are seeing them used in different context.

The 1.169" is the MAXIMUM OAL/COL according to SAAMI specs. The 1.090" OAL/COL listed in the load data tables is the length used for the testing of that powder charge and bullet. Seating much longer than the table listed OAL will reduce pressure and probably velocity, while seating to a shorter OAL/COl tehn tested will increase pressures, so be careful and work from lower starting point.

[slomo]

NWP, please explain how seating shorter increases pressure and seating longer decreases pressure. Thanks

[5pins]

NWP, please explain how seating shorter increases pressure and seating longer decreases pressure. Thanks

Seating deeper decreases case volume and seating longer will increase case volume.

[NWPilgrim]

NWP, please explain how seating shorter increases pressure and seating longer decreases pressure. Thanks

From Lee Reloading manual page 714:
Minimum Over All Length: This is critical on most handgun cases. A small reduction in overall length can cause dangerous pressures because of reduced capacity caused by seating the bullet too deep. See details on page 123. Best accuracy is usually obtained with bullets seated at the maximum overall length and factory crimped.

From Lee Reloading manual page 123:
The extreme expansion (XTP and Gold Dot) handgun bullets have a large and deep nose cavity that makes them longer than a regular bullet of the same weight. This requires deeper seating depth resulting in higher pressure. Seating depth is very critical for handgun ammunition because of the small cases and large bores. He then gives and example of seating a bullet 1/16" deeper in .270 rifle case and .45ACP case: results in 1.7% reduction of volume in .270 and 14% reduction for .45ACP. Plus, handguns have a much lower pressure limit than rifles so it becomes even more critical.

I have seen dramatic reduction in velocity with the same .40 S&W loads just by seating to a long OAL. Like about 100fps slower for .020" increase.

Then you have to consider that some powders burn differently under more or less case volume or if they are compressed or not.

This relationship can be reversed for rifle cartridges if the OAL is longer than max and the bullet is seated to contact the rifling or too near it. If the bullet contacts the rifling (good for accuracy) it does not have any time to get a running start before engaging the rifling and pressures can increase, loads should be reduced if seated to that length.