Firing wet ammo- Learned something today

[EastHumboldt]

At the range today a snow squall blew in and got all my stuff sprinkled with snow. It was just barely warm enough that it turned into water droplets right away. It was getting pretty snotty but I wanted one last five round group. I loaded five rounds from the box into a magazine, and took five more shots. The ammo had a few droplets on it, but I’ve shot under these conditions before so I wasn’t worried. The last two rounds, I had hard bolt lift and noticeable extractor swipe marks. I’ve fired probably 120 rounds of this particular hand load prior with no pressure signs, so I was surprised.

I don’t know if I’ve never seen this before, or just never noticed it before. I’ve been hunting for 40 years often in snotty weather.

I looked it up when I got home and found an article explaining why it happens. Who knew it’s a thing! I understand now what the science is, but I don’t understand why the first 3 rounds were fine and the last 2 were hot.

Anyone else experience this?

 

[ShortMagFan]

Water on the ammo or in the chamber definitely raises pressure!

 

[WCB]

I've seen it a bunch. Casings normally have tell tale "water droplet" marks. Same with over lubed/oiled chambers.

 

[Dioni A]

I went from no pressure signs to blowing primers out and locking my gun up on a hunt in Alaska last year because of this. My new standard is two grains below wherever I see pressure for medium size cartridges. The load blowing primers out was one grain under where I'd seen pressure.

 

[khuber84]

Liquids aren't compressable, that fluid occupied space the brass was supposed to be able to expand to. Wet chambers typically show pressure. I "water test" my match gun loads. Pour a bottle of water through the loaded 10rd mag, shake the water out, as a guy would in the field shooting, and send it. If I don't have pressure signs, that's an all weather safe load.

 

[EastHumboldt]

Anybody have it happen with factory ammo? My typical hand loads are probably around 1/2 grain less than where I see pressure signs. Looks like I might want to drop it a little more.

 

[hereinaz]

This is a well known problem for field condition match shooters. It’s why I get a larger case that gives me the speed I want, not pushing a small case to the pressure edge.

If all 5 were loaded the same, the issue was probably more water in the chamber the last two shots. The last two may have had more water from drops that fell down or accumulating water in the chamber.

 

[WCB]

Anybody have it happen with factory ammo? My typical hand loads are probably around 1/2 grain less than where I see pressure signs. Looks like I might want to drop it a little more.

I have not had it happen to me but have seen it with factory ammo many times.

 

[Lawnboi]

Very common. All the reason to not load right to pressure.

 

[hereinaz]

I have not had it happen to me but have seen it with factory ammo many times.

It is possible with any ammo.

One of the factors is the size of the case in relation to the chamber. When water fills the gaps between the case and chamber, it can cause increased pressure.

Also, as I understand it, heavy bolt lift and “pressure marks” can show if the water/oil reduces the friction between the brass and the chamber wall. This causes “excessive bolt thrust” where the brass gets forcibly shoved against the bolt face. It presses the brass into the bolt and the excessive pressure against the bolt after the brass finishes expanding causes heavy bolt lift.

The chamber walls need a specific amount of grip to stop excessive bolt thrust, but not too much that it get stuck. You can’t polish a chamber to a mirror finish for this reason.

Others can correct any possible misunderstanding.

 

[Lawnboi]

Anybody have it happen with factory ammo? My typical hand loads are probably around 1/2 grain less than where I see pressure signs. Looks like I might want to drop it a little more.

Even a lower pressure load, fired wet, will likely torch the brass.

Keeping it below case/primer failure is the goal here in my experience.

Factory ammo is pressure tested. I’m assuming there is some margin for error between max load and kaboom

 

[24valve]

Happened to me at the Winter S2H course a couple weeks ago with reloads just below book max occasionally blowing primers that showed no pressure signs when dry.

Thread 'S2H Winter Rifle Course Observations/lessons'

Feb 25, 2025

Shoot2Hunt held a Winter version of the 0-600 Yard Hunting Course last week. Below will follow some of the notable experiences/information.

@Ryan Avery @ztc92 @jzeblaz @longrangelead @24valve



Day 1: We started the afternoon before the official start date with 4x students and 2x teachers. 2x Tikka T3’s, 1x BAT action custom, 1x Tikka M595 Master Sporter. IIRC it was 3° F. Snowed all day.




Four more shooters arrived that night or the next morning.



The first four days it ranged from 3° F to -15°F for the day time...

• Formidilosus
• Replies: 198
• Forum: Firearms

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I'll be following @Dioni A's recommendation of 2 grains below pressure signs moving forwards.

 

[HairyScandinavian]

How'd that group look, OP?

 

[EastHumboldt]

How'd that group look, OP?

About average for me. About 3” horizontally, and 1-1/2” vertically. I was shooting at 200 yards, and could barely see the target through the snow. I can’t say any of the shots were wildly out of whack because of the pressure difference. I wasn’t running a chronograph, so I don’t know about the velocity.

 

[General RE LEE]

I’m loaded 2 grains below pressure. Super accurate and zero markings on brass. Long primer pocket life too.

 

[deadwolf]

There’s a lot of talk in this thread, and I’m not saying it’s entirely wrong, about being loaded such and such grains under where you’ve seen pressure. This in and of itself isn’t enough to ensure you won’t have over pressure when you fire a wet piece of brass. You need to ensure that your brass is sized correctly allowing enough expansion if your ammo happens to be wet or you get even a tiny piece of debris in the chamber. In older rifles and with “sloppy” chambers, and in the days before so many good hand loaders came along, it was never really much of an issue. Now with very tightly cut chambers, and people loading ammo that is super close or at the lands, there isn’t much give for any extra pressure. Sam Millard at Panhandle Precision had a good discussion about this very issue in one of his videos.


Sent from my iPhone using Tapatalk

 

[tt_johnsclist]

I’ve seen this happen with factory ammo that came out of factory boxes where the ammo was inside those molded styrofoam inserts. The styrofoam was degraded and the ammo came out covered in little styrofoam beads, loaded and fired, mild pressure signs and dented cases from styrofoam inside the chamber.