Effect of Cold Weather on Ammo?

[Kevin B.]

I noted a fairly substantial shift in my POI during the winter last year. My first shot was typically ~4" high at 25 yards. The second normally half that. The third and subsequent shots were back to POA. At first I thought it was me, but I was shooting daily and the anomaly was presenting itself each time.

We kicked around cold ammo, cold gun, some comination of ammo & gun temperatures and condensation in the barrrel but were never able to isolate the cause. Defintely a factor though. As the weather turned warm, it disappeared. Weird.

[Symmetry]

I have been known to leave a gun in the freezer overnight, or in the trunk on really cold days or nights, and then do a test shoot.


I have seen function issues with some guns, some ammo, and some lubes. Cold can also effect your ammo performance; http://looserounds.com/2014/10/01/th...little-secret/

I ran 15 rounds of Speer .38spl 135gr+P GD short barrel through a chronograph this morning. Temperature was 21 degrees F, and I left the ammo outside over night. Average velocity from a S&W M&P340 1.87"bbl was 842fps, with a lowest velocity of 828fps. I'm not sure what Andrew is doing with that ammo, but he is getting almost 100fps slower with his setup.

[RevolverRob]

Just out of curiosity - Has anyone actually taken the temperature of a gun carried "close to the body" versus "away from the body" in the winter? I've only got anecdotally limited experience, but so far, when it's 10-15 degrees outside and I'm standing at a bus stop for say, 15 minutes, even the items inside my pockets that are pressed up against my core (say the things that are in the inside pockets of my fleece vest that is over my baselayer, where I am the warmest), are COLD. I'm actually having a hard time imaging that your gun is 95 degrees carried IWB if you've been outside in low temperatures for an extended period of time.

Anyways, moving on to the effect on ammo - this is very interesting info here. I've always carried +P lead HPs in my revolvers year round. The soft lead tends to be reliable in its expansion, but if cloth clogs the cavity and prevents it from expanding, you are still pushing a +P semi-wadcutter on through with decent penetration. Seems like that might be a prudent choice if you're a revolver packer.

[5pins]

It would be interesting to conduct a test similar to this but actually use a chronograph.

https://www.youtube.com/watch?v=mlZ4R-bXpgI

[Symmetry]

I ran some more of the Speer .38spl 135gr+P Gold Dots through my S&W M&P .340 this morning. I cleaned the revolver thoroughly last night, and left both the pistol and ammo outside overnight. The low was 12 degrees F, and I tested the ammo at 14 degrees F. Average velocity out of a ten shot group was 838fps, with a low of 827fsp.

My theory on Andrew's low velocities during his gel testing is either he has a batch of ammo that's powder charge is temperature sensitive, and/or his revolver has too much gap between the cylinder and barrel resulting in too much gas escaping. Generally Speer, along with most defensive ammo manufacturers use low flash powders that are not as sensitive to temperature fluxes. Whether it be Hodgdon's extreme powders, or Vihtavuori powders, certain brands are very resistant to low temperature environments. When I lived my Montana, by Vihtavouri reloads showed very little velocity loss even at -20 degrees.

[Moonshot]

I ran some more of the Speer .38spl 135gr+P Gold Dots through my S&W M&P .340 this morning. I cleaned the revolver thoroughly last night, and left both the pistol and ammo outside overnight. The low was 12 degrees F, and I tested the ammo at 14 degrees F. Average velocity out of a ten shot group was 838fps, with a low of 827fsp.

My theory on Andrew's low velocities during his gel testing is either he has a batch of ammo that's powder charge is temperature sensitive, and/or his revolver has too much gap between the cylinder and barrel resulting in too much gas escaping.

That's very interesting. Could you both measure and post the barrel cylinder gap on your respective guns? That would confirm or refute that theory. As for powder, would a commercial ammo manufacture such as Speer use different powders in different lots of the same ammo? I would think that would introduce too much potential variation in performance to be acceptable.

[Symmetry]

That's very interesting. Could you both measure and post the barrel cylinder gap on your respective guns? That would confirm or refute that theory. As for powder, would a commercial ammo manufacture such as Speer use different powders in different lots of the same ammo? I would think that would introduce too much potential variation in performance to be acceptable.

I had a trigger job done on it recently, and the gap was measured at .008" at room temperature. I'm sure it opened up a little with the cold, but it would have closed as the gun heated up during firing. The M&P is a higher dollar gun in the smith line, so quality controls are a little tighter compared to the cheaper revolver models.

As for different powder used, most manufacturers stick with a handful of powder types depending on availability. Lot numbers change as different components may be used.

[Chuck Haggard]

Lot to lot variations with ammo also happen. I know Doc has seen failure to expand issues with the 135gr Gold Dot in the past and I recall that ammo being down into the 700fps range on the crono

[Symmetry]

Lot to lot variations with ammo also happen. I know Doc has seen failure to expand issues with the 135gr Gold Dot in the past and I recall that ammo being down into the 700fps range on the crono

This is definitely why everyone should have their own chronograph, and test the lot of ammo they intend to use for defense to make sure it is close to the factory specs.

[Gio]

Extreme hot or cold has different effects on different powders. Some are inverse temp sensitive, i.e they get slower as it gets hotter. Keep in mind, bullets are designed to operate within a specific velocity window. If you get outside of that you will potentially see issues with expansion (if too slow) or fragmentation (if too fast). Ammunition manufacturers already have to design bullets that perform well across the widest range of velocities possible to account for shooting out of different firearms and barrel length. Think about a 9mm bullet shot from a G26 and an H&K MP5. Adding temp variation on one extreme out of your specific gun could be enough to cause these types of failures.

A whole other cold weather phenomenon is powders that will actually blow up your gun in extreme cold weather (think -40 or below). There is a change in the chemical and physical make up of some powders at this temp that can cause this. My agency tested some very popular self defense loads that did this.