C.O.L vs. O.A.L Questions-concerns

[gerrym526]

Just loaded some 9mm using the Lyman guide. As a general practice, I load to just under the C.O.L (maximum overall length in the diagram), which is 1.169. My overall length for the loaded cartridge is about 1.166.

However, looking at the data panel for 147 TRN bullets, the O.A.L is show as 1.115-a big difference.

I've been reloading for about 1.5yrs now and adapted the practice of loading to just under C.O.L when I found my 45ACP rounds fed extremely well in a finicky 1911 Gold Cup (ie. no jams or misfeeds in 200 rounds).

Part of my reloading method includes the test that uses a dummy round dropped into the barrel of the gun I'm using to make sure it falls in/out smoothly-in the case of the 9mm it does. I then do an additional test by using a couple of dummy rounds in the magazine of the gun to make sure they chamber smoothly and fully-they do. (Gun is a Beretta 92FS).

My question is related to safety. Should I be following the OAL shown in the Lyman data panel for a particular round religiously, or is my technique of loading to just under the C.O.L and running the dummy round tests a safe practice.

Assume that all rounds are loaded within the Lyman guidelines for the powder used.

Thanks for the help guys.
Gerry

 

[LiveLife]

I never use the published OALs that are listed on the load data because often test barrel fixtures (and not real pistols) were used to measure average maximum chamber pressures and won't ensure the listed OALs will work with semi-auto pistols to reliably cycle the slides.

OAL that will work with your pistol/barrel depends on the start of rifling and leade/freebore length.

If your barrel has slower start of rifling with longer leade/freebore, then longer OAL will work. Of course, using shorter OAL may work as well but if you are using lead bullets, more high pressure gas will leak around the bullet as the bullet takes longer to engage the start of rifling to build chamber pressures (during which time more liquefied lube will be blown off the bullet and gas cutting/leading will result).

To minimize high pressure gas leakage and increase accuracy, conducting the barrel drop test to determine the Max OAL and function checking by feeding from the magazine is a good idea.

 

[gamestalker]

About the only element of OAL I utilize is for pressure purposes. If the firearm I'm loading for will accept longer OAL's than the published, I use the longer fitted OAL so I don't experience pressure issues, especially with 9mm and .40 cal. Pressures can really jump up with those small high pressure cartridge, even with nominal differences of .010" or so can cause pressures to rise noticeably.

GS

 

[gerrym526]

OK-I Think I Understand Your Responses

Thanks to both of you for responding. If I understand your responses, the longer the OAL (within acceptable feed and fit dimensions), the sooner the bullet will engage the lands/grooves in the barrel, minimizing any escaping gases and lowering the pressure so as not to damage the chamber.

Did I get it right?

Thanks again for the help.
Gerry

 

[gamestalker]

10-4, you understand.
GS

 

[LiveLife]

The reason why we want to reduce gas leakage is to produce more consistent chamber pressures which will produce more consistent muzzle velocities which in turn translates to smaller shot groups.

If shooting lead bullets, less gas leakage will reduce leading and also improve accuracy as outlined above.

 

[bearauto11]

Are you sure the 1.115" isn't a minimum? In the book I'm looking at, it has a max listed, then the loads have a minimum.
--Tom

 

[lindy]

Max C.O.L. is normally given to insure the cartridge will fit into the magazine.

Good Shooting

Lindy

 

[david_r]

AS TESTED or MINIMUM is normally given in the data. Pressure doesn't mean anything unless you know how long the round is as pressure is indirectly proportional to case volume. Ask someone with quickload to run your 9mm data with a COL of 1.000" and report back on the pressure.

If you load over the listed COL and your rounds pass the plunk test, you should be good to go as you will be running lower than tested pressure. If you load under the COL you will be increasing pressure; maybe catastrophically.

SAAMI drawing for 9mm Luger. Minimum Cartridge length 1.00" Maximum Cartridge length 1.169"
Speer: "Max. Cart Length: 1.168"." "C.O.L. Tested At" ALL listed data under the Max. Cart. Length
Lee: Cartridge drawing length - 1.169". "Miminum[sic] OAL" ALL data under the cartridge drawing length
Accurate Powders: ALL data under the SAAMI Maximum Cartridge Length
Every other powder/bullet mfg data I have read: ALL data under the SAAMI Maximum Cartridge Length.
There seems to be a pattern there.

Gerry,
Yours is a safe practice.
You are likely loading to a lower velocity and pressure by loading so far out from that data's COL. If it fits your magazine, cycles your gun, feeds reliably, head spaces properly, puts your rounds down range and you are happy with it, great. Leave well enough alone. Only possible concern would be squib loads.

If you are going to shoot those reloads in another gun, you will want to make sure they aren't hitting anywhere but the mouth by dropping them in the barrel like you do with your current gun.

 

[Lost Sheep]

Mostly correct

AS TESTED or MINIMUM is normally given in the data. Pressure doesn't mean anything unless you know how long the round is as pressure is indirectly proportional to case volume. Ask someone with quickload to run your 9mm data with a COL of 1.000" and report back on the pressure.
(I italicized the text I am addressing)

Within some range it may be a proportional/linear relationship, but at some point the relationship goes hyperbolic and pressures skyrocket (at the high end) or plunge (at the low end) to where the powder burn becomes unstable.

Otherwise, right on target.

Lost Sheep

 

[ljnowell]

I try to never load under min OAL, though I have afew times. I always load a round as long as I can for an autoloader. As long as it fits all the magazines and chambers in all the guns I will fire it in. Thats what I look for. Wherever that falls, well, thats what it is.