Bullet Seating Depth

With the latest round of COVID taking its toll on firearms and ammunition suppliers, I’ve spent the past couple days working up a new load for my 45ACP’s. The reason I’m not using my “Tried and True” load data that I typically use as my standard “recipe”, I’ve been forced (as with many other hand loaders) to purchase what ever I can get my hands on in order to continue to practice and enjoy shooting.

One of my favorite handgun calibers to shoot is the .45ACP. It’s a great round to shoot, a FUN round to shoot (especially from a 1911), is a “Hard Hitting” round, and is accurate to boot…. that is, as long as the pistol is properly maintained and the ammo is accurate (why I hand load).

The very first time I hand loaded was when I loaded and shot my first black powder rifle years ago. Now, it’s pretty much all modern guns, but the concept is pretty much the same other than that I’m loading a cartridge instead of a gun barrel. The one thing that has always stuck in my mind from muzzle loading is that the more variables that are removed from the loading process, the more consistent the end results will be.

One of the things that most people may not fully understand is the effect bullet seating depth, commonly referred to as “Case Overall Length” (C.O.A.L). All reloading guides list specifications for ammo “recipes” that spell out each component in the bullet build – one of those items is COAL. Although the overall length of any round is an important factor in reloading, the numbers listed are the “standards”. Now before I go any farther, standards to me are just that….. no more than a somewhat starting point to work from.

Having purchased a few pounds of a powder that I’ve never tried, and using projectiles that I’ve never tried was almost like starting all over from scratch. Given that, I typically like to see an average velocity of about 850fps out of my 1911’s when firing JHP’s (Jacketed Hollow Points) since that velocity produces average of about 375 FT-LBS of energy which will allow the bullet to penetrate and expand as designed making it a viable hunting/defense round.

The recipe I built today uses a combination of Hodgdon “TiteGroup” powder under a 230 grain Winchester FMJ projectile. When reloading it’s always best to start with a low charge of powder and work up while keeping all other variables such as COAL per specifications. Since I’ve loaded so many of these things using all sorts of combinations in the past (I keep an accurate log of my test loads), I had a pretty good idea as to what powder charge would put me into the 850fps range. My first test proved to be pretty much spot on producing an average velocity of 865fps with a COAL of 1.215″ (specs call for 1.210″) and a spread of 1.25″ @15 Yds. Not acceptable….

Chronograph feeds velocity data to iPad. (NOTE: Lead bars used as barrel rest weights)

I then readjusted my press and using the same powder charge, set the COAL out to 1.225″, giving an additional 0.015″ in length placing the projectile that much closer to the rifling lands in the barrel. Although the average velocity dropped to 833fps, the overall spread opened up substantially to 1.60″…. No way Jose!!

My third test was to readjust my press and using the same powder charge adjusted the COAL in to 1.205″, reducing COAL by 0.020″ from test #2 giving the bullet a little more “jump” to the rifling lands in the barrel. Average velocity when up substantially to an average 860fps, and a 3 round group produced an overall spread of 0.450″. YES!

I then loaded 8 rounds to validate my findings. Six of the loads were loaded as per the the result of test #3 with COAL’s of 1.205″. I loaded one round with a COAL of 1.225″ (Test #2), and another with a COAL of 1.215″ (Test #1). I mixed the loads up when I loaded them into the magazine so I wouldn’t know when the two misfits would fire. I do believe that the test results pretty much speaks for itself!!

(L-R, Test #1; Test #2; Test #3… Bottom – Validation Test)

In closing, I do want to point out that I never use COAL when building ammo. I used the term within this content since it’s easily understood, and is a defined standard in all reloading manuals.

When using COAL as a defined setting, one needs to understand that most bullets produced by the same manufacturer/supplier, produced from the same batch will all differ in length…. Lead tipped projectiles are the worst and can vary in measured length up to around .020″! Although FMJ’s (Full Metal Jackets) are a bit closer in length, I have seen variances of 0.005″ with them. As a hand loader, I use a much more accurate measurement when seating bullets – I use an “Ogive” (pronounced: OH’jyve). It is used in engineering, and is the roundly tapered end of a two or three dimensional object.

To measure ogive when seating bullets, I use a Headspace Comparator Kit that attaches to one of my micrometers. At some point, the projectile’s curve will make solid contact with the surface of the comparator at which point I make note of the reading on the micrometer. Using an ogive measurement instead of a COAL measurement, I am able to recreate consistent loads time and time again since I am no longer relying on the inconsistencies of variable lengths of projectiles.

Seeing how just a few thousandths of an inch can change accuracy in a load, removing the variable of COAL and replacing it with an OGIVE measurement makes total sense….

Measuring bullet ogive using a .45 comparator
Spread the love

Leave a Reply

Your email address will not be published. Required fields are marked *