Pressure signs in cold weather

[Smithb9841]

Not sure if this should be posted here or reloading or firearms section, but here goes. Has anyone ever seen pressure signs when hunting in cold weather? The reason I ask is on my 4th season deer hunt, I had heavy bolt lift and ejector marks with all 3 of my shots I fired. I was shooting my own reloads, these aren’t loads that were pushing the envelope or trying to squeak every fps out of the load by any means. The load was with H4831sc so as far as I know a relatively temperature stable powder ( I could be wrong on this but that’s my understanding).

I believe the weather got down to around -6 that morning gun was placed on ground with bipod extended so close to the snow but not like the action was buried in snow before the shot. This was on a rifle with a tikka action and a proof carbon barrel not sure if that matters or not. Have shot a probably a 150-200 rounds with this exact same load. No reason to believe powder scale went out of whack and I over loaded a couple rounds. This is with a 6.5 prc shooting 156 bergers with H4831sc

Obviously metal contracts in cold but would cold weather be enough to cause an issue which would effect this much? Will be going back out to the range hopefully this weekend to shoot a couple more out of same batch that these are loaded in at normal temps. But figured I’d see others opinion on this.

 

[dirtytough]

With one of my rifles that I tested I was shooting an average of 30 fps faster in cold weather. So if the exact same load is going faster I would assume pressure is increasing.

 

[WV Mountaineer]

Yes. It can cause it. I’m assuming you aren’t intermixing new components with components you’ve loaded to shoot the loads you’ve shot previously. If so, start there.

 

[Duh]

I had this with Varget the other day. 35.5 grains in a 22-250 was not showing pressure signs at all when load dev at 60 degrees. Then shooting it at 25ish degrees, I started to get a bit of sticky bolt lift and swipe marks.

 

[Smithb9841]

Yes. It can cause it. I’m assuming you aren’t intermixing new components with components you’ve loaded to shoot the loads you’ve shot previously. If so, start there.

Thanks for responding.
No mixing, nothing changed with the loads same powder container same primers.

 

[Smithb9841]

Thanks for the replies guys

 

[RockAndSage]

Something to watch out for in extreme cold can be moisture condensation - moisture on a casing can cause overpressure. In sub-freezing weather it's best to keep both the ammo and rifle outside of the heated areas, leaving them in the cold. What's especially problematic is repeatedly moving in and out of heated areas into the cold and back, such as a tent or a vehicle. The condensation will build up as frost and/or ice, and can lock a gun up solid. This is part of what's taught at Fort Wainwright's arctic warfare training programs.

Now, all that said, I've never heard of any of this (arctic or sub-zero operations) related to cartridge over-pressure. But, I do know that it's very common for PRS guys and people loading to the edge of overpressure to go past that edge while firing in the rain. Just a little raindrop moisture on the cartridge during cycling can be enough to cause overpressure. So, I don't know why a little hot/cold condensation couldn't do something similar.

 

[wind gypsy]

I have a 6 creed that might be seeing some similar issues in cold weather. I thought it was a barrel cleaning/ carbon ring thing because it went away when I cleaned the chamber good and then shot it in warmer weather and problems were gone. Was colder with some moisture in the air again today and the pressure signs are back. This is with 3 different kinds of factory ammo so not like it’s hot handloads.

Seems like bullshit a guy shouldn’t have to deal with. My other guns don’t have similar issues.

 

[RockAndSage]

That really is BS. The only other thing I can think of that might make any sense at all, would be tolerances so tight that they become too tight in the chamber if it gets cold enough because of metal shrinkage, but even that sounds as ridiculous as the problem itself.

 

[wind gypsy]

I have a 6 creed that might be seeing some similar issues in cold weather. I thought it was a barrel cleaning/ carbon ring thing because it went away when I cleaned the chamber good and then shot it in warmer weather and problems were gone. Was colder with some moisture in the air again today and the pressure signs are back. This is with 3 different kinds of factory ammo so not like it’s hot handloads.

Seems like bullshit a guy shouldn’t have to deal with. My other guns don’t have similar issues.

Similar temps today. I set the ammo and rifle outside to get to outdoor ambient temp before going to range. No cleaning or other changes since the last trip and there were no pressure signs observed.. weird.

 

[RockAndSage]

That's extremely interesting... now it makes me wonder if there's a reduction in pressure in cold weather if the powder is at ambient temps...

 

[Bluefish]

Interesting, I find I get reduced velocity and thus pressure in the cold. i do use a temperature sensitive powder. I could see if the gun is cold and the ammo warm or warmer than the gun that you could get pressure spikes. Ie you load from a pocket and the gun is ambient. Even the most stable powder should drop about 1/2 fps per deg F. That alone should reduce pressure as temperature decreases. Thermal expansion of brass is almost double that of steel, so the brass should be getting smaller faster than the steel. So maybe that is causing the pressure issues. Your brass volume is decreasing faster than powder burn rate is slowing down?

 

[wind gypsy]

I didn't do great chronoing each round but i have enough of a picture that the sticky bolt lift and ejector marks didn't seem to corelate to higher velocities.

I thought it might be a condensation thing but that seems backwards as there shouldn't be condensation on warm barrel/ammo with cold air? Wouldn't that require warm temps and cold barrel/ammo?

 

[Harvey_NW]

Shot in the dark here, but in one of the Hornady podcasts they talk about a perfect storm type situation where something like using a faster powder with less case density and shooting downhill with the powder bed farther from the primer pocket could change the internal combustion dynamics, and actually cause a pressure spike. They mention other variables that could cause it as well, so might be something like that.

Other thing that comes to mind that I've experienced is bullet weld if you don't lube necks, and are shooting ammo that's been sitting for a period of time. Run a couple rounds through the seating die and bump them a couple thou, should here the weld pop if that's the issue. I lube necks with graphite powder now and have not had issues since.

 

[manitou1]

I was getting ready to post what Harvey (above) said about bullet weld.

I have experienced this. When I find a load that works for a rifle I have a tendency to load up a few hundred rounds for hunting. The dissimilar metals can "weld" together causing a pressure spike upon firing.
This has only happened on one rifle of mine... a custom with a very snug chamber.

Solution: Load bullets .002" long and before shooting put them in your bullet seater and seat them .002" deeper, essentially breaking the bond between bullet and case mouth.

 

[wind gypsy]

Cold weld may be a thing for the OP, definitely not for me as the same ammo has rotated between having/not having pressure signs the last 4 trips to the range. The pressure signs were seen on multiple different types of factory ammo. Sig 107 SMK and hornady black 105 bthp were basically 100% sticky bolt lift on a couple days, 108 ELDm factory was maybe 50%, norma 107 golden target has shown it too. Primarily the Sig ammo (which is crimped) that I bought $500 worth after successful initial trip is the one I just want to work without issue.

 

[Smithb9841]

Thanks for the responses guys meant to come back and update anyway. Went out to the range a couple weeks ago and had the same issue heavy bolt lift, flattened primer, and heavy ejector mark and this was in 50-60 degree weather so similar weather to what the load was developed in.

My buddy had the idea to run back to his house and we bumped the seating depth a bit to match his load that he shoots for 5 rounds and then went back to range. Tried 5 shots and had a little bit of a sticky bolt lift wouldn’t exactly call it heavy and a very slight ejector mark. Luckily this load shot great in my rifle so I plan to bump the seating depth back on all my loaded ammo. Also just to verify we pulled the bullets on several of my rounds to verify powder was consistent and I didn’t have an issue with my scale/dispenser when I was loading and they were all dead on.

I gave the rifle a good cleaning tonight as a last ditch effort it’s been somewhere around 150-200 rounds since I cleaned it so not sure if that’ll matter at all.