COL dimensions

[chiefster233]

I understand that reloading data tables give a "minimum COL" so as to prevent reloaders from producing a dangerous compressed load. So, does it make any difference what our COL is, provided it is at or above the minimum dimension? I'm talking about a 9mm pistol cartridge here. Some bullets I load have a recommended a minimum COL of 1.1". My Glock seems to function with COLs way longer that this. So, is there any advantage to producing a longer cartridge or is any COL above the minimum OK?

I know that rifle reloaders want their cartridges to be as long as possible to increase accuracy. Just wondering if this is a big deal with 9mm reloaders.

I've been loading 115 grain and 147 grain to a 1.14" and 1.15" COL with no ill effects but I wonder if I'm losing some accuracy by doing this.

Thanks!

[jwrowland77]

There is an advantage in my eyes to loading to 1.14/1.15 etc....it keeps the load safe, especially in a high pressure round like 9mm. My best 9mm load has a col of 1.150 using 115gr. Will probably use close to the same with the 124gr I have.

I used to use close to the max SAAMI col of 1.169. That's the regulations I go by.

I used to use 1.165 but found out when I was shooting steel challenge, I was having issues cycling while trying to shooting quickly. I changed my col to 1.15 and the issues went away.

[g.willikers]

I load to the maximum length that fit the mag, the chamber, and will function in the gun.
With the appropriate amount of powder to achieve desired velocity, always staying well within published and observed safe limits, of course.
This will vary with bullet weights and lengths, natchurely.
Leaving as much volume under the bullet as possible allows for mistakes and/or reloading and gun functioning anomalies.
Like crap getting in the bullet seating die, the die winding in the press on its own, or rounds hitting the feed ramp, resulting in bullets seating deeper than intended.
Just a precaution I've always done without any apparent downside.

[Sevens]

Some things about COAL that occur to me that might be worth sharing.

You should always record the COAL of any/every handgun round you build. About the only time I would say it's not critical is if you are using a strictly cannelured bullet, and loading to that cannelure, because as long as you are using the same bullet, loading to the cannelure is always going to give you the same COAL. But recording (and repeating!) the COAL is as important and recording the powder charge weight. Because altering the COAL (especially in a high pressure and/or relatively short cartridge) affects the performance of the round on a large basis.

You are correct in that published "minimum COAL" is important because pressures can rise dramatically when the internal combustion space is reduced, but understand that it's NOT about COAL, it is absolutely about the internal combustion space. Published COAL minimums are only relevant when working with a bullet of the same shape & length as the one referred to in the published source.

So, does it make any difference what our COL is, provided it is at or above the minimum dimension?

Certainly, it makes a difference. When you build them at a l-o-n-g COAL, you might first run in to issues fitting them properly in your pistol's chamber. You may then find issues fitting them properly in to your pistol's magazine. And that's after knowing full well that when all else is equal, a longer COAL with more internal combustion space is running a LOWER pressure than expected or planned from running a typical COAL.

If your pistol's chamber likes them, that's good!
If your pistol's magazine accepts them, that's good!
If your gun runs properly 100% of the time with a "less than full pressure" load, that's great and you are good to go.

...Now when you get yourself all addicted to that load that runs so well for you, all is good, all is fine and all is well. UNTIL... You get another 9mm pistol and you find that your ammo won't run in it well (or at all!) because of one of the three possible issues above.

At that point, you can begin to customer tailor two different "favorite" 9mm ammo supplies for your two different pistols if you like. But it gets to be a hassle, IMO.