Which is best short COAL w/ less powder or long COAL w/ more powder

[wondering121]

I'm relatively new to handloading (just been doing it a few years) and I recently got into loading 9mm. My Lyman 50th Edition manual only shows data for 124 grain JHP and the COAL is only 1.060" (compared to the SAAMI max of 1.169").

My Nosler 8th Edition only lists by bullet weight and their 124 grain COAL is 1.120" Just for reference the manuals list minimum loads using Unique as:

Lyman - 4.0 grains at 975 fps
Nosler - 4.6 grains at 981 fps

I loaded the Lyman load and the rounds just seemed very short (almost looked like 380 ACP) rounds. They shot fine ejection was weak, but the slide cycled fine.

I'm a bit hesitant to go with the shorter COAL because of potential effects on pressure, but my question to you all is this: faced with this information is it better to go with the shorter COAL and save some powder or is it worth it to use the extra powder and go with a longer COAL?

Thanks in advance

[jag2]

Those both look very anemic. I didn't know you could get a 9mm to go that slow. You aren't anywhere near the worry zone. Check your manuals for a more midrange load and give them a try.

[Nick_C_S]

Your question is kind of moot.

You want the correct COAL for your bullet/gun. Your two sources gave different COALs because they likely used different bullets with different ogives (nose shape). For instance, a blunt stubby hollow point will likely require a much shorter COAL than a pointy round nose. And even round nose to round nose is not apples to apples. A more oval shaped round nose will likely require a shorter COAL than an elliptical shaped round nose.

Ideally, the bullet you use should be tested in your gun's barrel, via "plunk test," followed by a mag test to make sure they fit in the gun's mags. Admittedly, I often use the manual's COAL if I have that data (Speer bullet - Speer manual; Hornady bullet - Hornady manual, etc.), and doing so has served me well enough. But most of the time, we don't have access to that data - you mention Lyman and Nosler data; but are you using a Lyman or Nosler bullet?

To address your basic question: All things being equal (and they rarely are), a shorter COAL will yield a faster propellant burn rate and correspondingly higher peak pressure. This could be good or bad. It could mean a more consistent, clean burn, yielding excellent ammo. Or it could cause a high pressure situation and all that implies. But again, this is moot because you want the "correct" COAL.

[74A95]

Originally Posted by wondering121

I'm relatively new to handloading (just been doing it a few years) and I recently got into loading 9mm. My Lyman 50th Edition manual only shows data for 124 grain JHP and the COAL is only 1.060" (compared to the SAAMI max of 1.169").

My Nosler 8th Edition only lists by bullet weight and their 124 grain COAL is 1.120" Just for reference the manuals list minimum loads using Unique as:

Lyman - 4.0 grains at 975 fps
Nosler - 4.6 grains at 981 fps

I loaded the Lyman load and the rounds just seemed very short (almost looked like 380 ACP) rounds. They shot fine ejection was weak, but the slide cycled fine.

I'm a bit hesitant to go with the shorter COAL because of potential effects on pressure, but my question to you all is this: faced with this information is it better to go with the shorter COAL and save some powder or is it worth it to use the extra powder and go with a longer COAL?

With respect to pressure, the load manuals take that into account, so as long as you follow their recipe, you're okay.

There's really no 'better' unless you're looking for the fastest speed possible. In that case, a longer OAL allows more space in the case (if using the same bullet). This allows a little extra powder to gain a few more fps. It's not a huge difference, but every little bit of chamber space makes a little difference.

[Unclenick]

That's correct. The longer you seat, the more powder it takes to reach a specific velocity, but it is getting there at a lower peak pressure because the extra gas from the added powder keeps up higher post-peak pressure down the length of the barrel, adding more to the acceleration of the bullet. As a practical matter, that lower peak pressure means you can safely increase the charge, getting to a higher final velocity for the same peak pressure as that same powder could give you with a shorter COL. If powder charge economy is your objective, find the combination of the shortest COL and highest still-safe peak pressure with the highest energy powder that produces the velocity you want. That will prove to need the lowest charge weight.

[44 AMP]

For instance, a blunt stubby hollow point will likely require a much shorter COAL than a pointy round nose. And even round nose to round nose is not apples to apples. A more oval shaped round nose will likely require a shorter COAL than an elliptical shaped round nose.

While essentially correct, I would restate this to say "results in" rather than "requires".

The way I look at it, the data giving COAL is not a figure that you have to go to, its what they got when they measured it. When you look in the books and see a max loaded length, its a number to stay UNDER, in order to have your ammo work in all the different guns out there. In 9mm pistols, if it fits in the chamber and in the magazine (all the way up and down) and feeds, small differences in the 0.0xx range are usually not significant.

Lyman - 4.0 grains at 975 fps
Nosler - 4.6 grains at 981 fps

These loads are a bit light, original 1902 9mm Luger loading was a 124gr @ 1050fps from a 4" barrel.

[Unclenick]

I will add that because bullet lengths differ, the powder space actually depends on seating depth (and slightly on whether you have a boattail or not) rather than COL. The formula is simple:

Seating Depth = Case Length + Bullet Length - COL

Unfortunately, the bullet makers are not all in the habit of giving you the lengths of their bullets. Nosler does, calling it the bullet's OAL, but I think you have to call the rest or hope it's listed in your copy of Litz's book, Ballistic Performance of Rifle Bullets.

More seating depth means less powder space. How much less can be garnered from this formula (though, again, I have omitted to account for boattail taper and length for simplicity):

Where:
r = half your bullet diameter in inches
d = seating depth in inches
c = case water overflow capacity (the weight of water level with the mouth that your case can hold) in grains of water weight
C = powder capacity in grains of water weight

C = c - 252.9(dπr²)

So, if you have, say, a .308 Win case with 57 grains case water overflow capacity and you seat a .308 caliber bullet into it to a depth of 0.4 inches, then your powder capacity under the bullet is:

C = 57 - (252.9 × 0.4 × π × .154²) = 49.5 grains water space.

If you want to get closer, you can calculate a boattail's actual volume.

Where:
h = length of boattail in inches
r = half your bullet diameter in inches
r' = half the diameter of the small end of the boattail in inches
V = boattail volume in grains water weight capacity

V = 252.9πh(r² + r'² + r r')/3

You then use the first formula, but with seating depth figured using the length of the bullet from the bottom of the bearing surface to tip rather than from the bottom of the boattail. Then subtract the boattail volume from that result to get final powder capacity.

You can also divide case water overflow capacity measured at room temperature by 0.997 to compensate for the fact water is slightly expanded at room temperature. All the calculated adjustments to case water capacity assume water has its 39.2°F density, which is the temperature at which water is most dense and is closest to 1 gram per cc.