45 ACP Brass Length

Having heard claims that pistol shells shrink with use whereas rifle shells stretch, coupled with the fact that in the 45 ACP 1911 the shell indexes* on the mouth of the shell, and with a recent comment from Kirk in mind, I decided to measure the length of various brass samples.

On-hand, I had five categories: brand new Starline, once-fired Remington, two flavors of “a few firings” (Winchester and Starline), and my practice brass that’s been fired and reloaded a dozen or so times.

I took ten (10) random samples of each and measured their lengths (in inches).

New
Starline
Once-fired
Remington
Multi-fired
Winchester
Multi-fired
Starline
Heavily-fired
Mixed
1 0.892 0.887 0.883 0.889 0.895
2 0.893 0.888 0.884 0.890 0.892
3 0.894 0.888 0.885 0.891 0.890
4 0.893 0.888 0.885 0.885 0.888
5 0.893 0.889 0.884 0.890 0.888
6 0.892 0.889 0.889 0.895 0.888
7 0.892 0.894 0.884 0.886 0.890
8 0.891 0.888 0.891 0.890 0.889
9 0.892 0.889 0.884 0.890 0.885
10 0.893 0.889 0.886 0.892 0.886
Min 0.891 0.887 0.883 0.885 0.885
Avg 0.8925 0.8889 0.8855 0.8898 0.8891
Max 0.894 0.894 0.891 0.895 0.895
StdDev 0.0008 0.0019 0.0025 0.0028 0.0029

The first thing that caught my attention was the StdDev (standard deviation). As the number of firings goes up, so does this number. Whatever the change, the variation in length becomes more pronounced as the number of firings goes up.

Next, look only at the two Starline columns and the Min and Avg lengths. (We’ll come back to the Max in just a second.)

Notice that, when fired, shells do seem to get shorter as I had heard. That’s what the Min and Avg numbers are showing for the two Starline columns.

But not the Max column!

The Max column is being thrown off by an anomalous shell. Look at #6 in the Multi-fired Starline column — it’s marked in light blue. It measured as 0.895″, the longest in that column and tied for length only once in the entire data set. That other shell is at the top of the Heavily-fired Mixed column and also marked in light blue.

If those two shells are removed and the numbers re-calculated (not shown here), there’s a very clear correlation between number of firings and shrinkage and, perhaps even more important, a greater and greater variation in overall length.

New brass (from one vendor) will almost certainly have the least amount of variation from one shell to the next — it will be the most consistent — whereas brass that’s been fired many times will have more and more variation in length.

At this point, it’s worth pointing out that while we think of accuracy as being the most important property of Bullseye ammunition, it’s actually the consistency of accuracy, from one round to the next, that really matters.

In other words, you can shoot different batches of ammunition that land all over the target but, as long as one batch shoots to the same location, you can center that batch on the X ring with sight adjustments. And as long as that batch continues to shoot with consistent accuracy and you don’t need to change to a different batch, then you can nail the center of the target over and over.

Consistent accuracy.

Is the amount of shrinkage seen here significant? Does it affect accuracy? Will it shoot consistently? Does it affect safety? Does it affect reliability?

Those are hard questions to answer without spending a lot of time sorting brass, reloading it into different batches and then carefully emptying it out again at the gun range.

Short of doing that, is there another authority that’ll provide some help?

Well, the SAAMI specification — that’s the “Voluntary Industry Performance Standards for Pressure and Velocity of Centerfire Pistol and Revolver Ammunition for the Use of Commercial Manufacturers” [phew!], or ANSI/SAAMI Z299.3-1993 — says the shell must be 0.888-0.898″ in length.

In my samples, none were too long but more than a dozen are too short.

Let me say that again:

In the above measurements of actual brass, not one piece of fired brass was too long. Not one. Many were “in spec” but several had become too short.

They’re marked in red. Most of them are in the Multi-fired Winchester batch. (Off-hand, I had expected the Heavily-fired Mixed category to have the most “under spec” shells, but it was the venerable Winchester brand that came in worst for length. Interesting! Have I fired those more than my notes suggest?)

Regardless, is it time to dump that brass? After all, 80% of the shells in that column were below spec.

And what about those “light strikes” I’ve been seeing? Could a “short shell” account for a light strike? I think they’ve been happening in the Heavily-fired Mixed batch and, for the samples measured here, 30% are below the minimum length.

So, if a round shifts forward in the chamber when struck on the rear by the firing pin, would it move far enough to not fire the primer and result in a light-strike?

Short brass = light strike?

Interesting possibility!

I’m suddenly tempted to sort through the piles of brass, find all the short ones, load up a box of them and see what happens.

Hmmmm!

____________________


* Note: “Indexing” is how a round’s position within the gun’s chamber is determined, by the contact of one surface of the round with one surface in the chamber. For the 45 ACP 1911 automatic pistol, those surfaces are the mouth of the shell and a slight ridge around the deep end of the chamber. When the round is inserted, it’s forward travel is limited by those two surfaces coming into contact. While a small amount of “play” is allowed such that these two surfaces may not actually come into contact with each other when a round is chambered, if the length of the shell is out of tolerance, either too long or too short, it may not work correctly.

2 thoughts on “45 ACP Brass Length

  1. Consider both length and diameter; the case thickness varies for different brands. Having said that, my limited accuracy testing (when trimming to length) has been inconclusive. I do sort by headstamp.

  2. Here’s something to keep in mind. I once had a notable BE smith tell me that most guns actually fire rounds that are too short. And as such the case will rest on the extractor instead of actually head-space on the rim.

    Unfortunately there are a few other variables to take into account.

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