Hot Stuff!

In the chronographing of various ammunitions and guns a few days ago I recorded the following five-shot string:

1 830.7
2 917.1
3 932.0
4 954.6
5 905.5

Notice anything interesting?

Well yes, the velocities are relatively low. The ammunition was RWS Subsonic and the gun was a Smith & Wesson Model 41 with the seven (7) inch barrel, but that’s not what caught my eye.

Let me add that, before the fifth and final shot, there was a delay of almost a minute. And it was relatively chilly that morning with temperature in the mid-50s, rainy at times, misty when not, and with a gusty wind that quickly drew away body heat.

What you may notice is what I did, that as the string progressed, the velocities went up and up. Then, on the last shot where I delayed before firing, the velocity dropped back down again.

I think these changes are due to the temperature of the ammunition, starting with a cold gun and chamber but with each successive shot warmed in the chamber from the heat left from the previous shot. And when I delayed before the last shot, the gun quickly cooled in the misty, breezy conditions to account for the reduced velocity of the last shot.

When shooting in competition, many have commented that their ammunition seems to be rather temperature sensitive. This comes to my mind when my Smith & Wesson 41 doesn’t cycle the next round properly. Be it a failure to extract, a stove pipe or the next round getting stuck halfway into the chamber, it seems that when the ammunition is cold these types of failures seem to be more common.

So on cold days I load the magazines for the next target and tuck them under my jacket and arm while scoring the previous target. That way, when I’m ready to shoot the next target, the ammo and magazine are nice and warm.

And I’ve often wondered, just how much difference is this making?

And from that, just how sensitive is my 41 to changes in velocity?

Since the above data suggested I was seeing this very effect that day, I devised a small experiment on the spot to try and quantify it.

Here’s the plan I created. It consists of two parts.

I would fire two groups of ten shots each, the first with a cold gun, ammunition and magazine for each shot, and the second where each was warm.

For the cold group, I would lay the pistol — the 41 — on the table along with the magazine and, spread out nearby, the ten rounds with lots of space inbetween. I would then wait a full minute to let everything cool.

I would then load one round into the magazine, ready the gun and fire, remove the magazine and lay them both back on the table. I would then note the velocity on the chrony’s display, look at the clock and finally wait sixty (60) seconds before repeating this “load and fire one shot” process.

Next, I would fire the warm group.

For the warm group, I would prepare and then hold a single magazine with ten (10) rounds along with another magazine with five (5) rounds under my arm for ten minutes (while shooting the cold string). The five round string would, hopefully, warm the gun for the following ten round string where I would record the “warm” velocities.

Following that plan, here are the “cold” and “warm” results I recorded:

Cold Warm
1 888.5 900.9
2 898.9 943.3
3 881.7 913.4
4 889.2 951.8
5 931.4 942.9
6 900.9 922.4
7 859.1 927.1
8 884.2 937.8
9 886.6 n.a.
10 n.a. n.a.
Minimum 859.1 900.9
Average 891.2 930.0
Maximum 931.4 951.8
Spread 72.3 50.9
Std.Dev. 19.3 17.2

(The “n.a.” values occurred in the middle of the strings when a particularly dark cloud blocked the sun and the chrony displayed “Err 2” meaning the second sensor had not recorded the passage of the bullet.)

Clearly, this shows that the warm ammunition in a warm magazine that is fired from a warmed chamber is not only faster by about 5%, but that is also is slightly more consistent in velocity (standard deviation of 17.2 versus the cold’s 19.3).

I am presuming, of course, that higher velocity means the recoil force will be larger and that, at least in my case, that difference accounts for the more reliable cycling with the warmer ammo.

Also “of course”, how this translates into accuracy on the target is a different matter. But in my quest to find ammunition and gun combinations that are both reliable and accurate, the former is a lot easier to determine.

And here we can see that temperature is significant.

Here, we can see a 5% change in muzzle velocity solely due to that one factor.

And in my quest for “reliable and accurate”, what this really does is widen, not narrow, my search.

Now that I know that ammunition that doesn’t have enough oomph to cycle the slide when cold may, if treated to some body heat, “warm” to the occasion, I also know that more brands of ammunition may work in my 41.

A little warmth and care can work wonders.

Hug a bullet today!

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