I ventured out to shoot on Saturday morning when it was -31C. Not too much fun, frostbite on my trigger finger still a little swollen. First 3 shots went very well, last two I had sticky bolt lift. No other signs of pressure in the primer, etc. I understand this condition can occur near max loads with excess oil in the chamber or lube on the case, but can frost do the same thing? The only thing different with the last two shots were that they had noticable frost on them from my handling them with bare hands. What do you guys think?
Sticky bolt lift from frost?
- Thread starter gillamboy
- Start date
Were these hand-loads? What cartridge? Was it a factory gun? Was it a stainless barrel?
BTW -31 is too cold for using stainless barrels safely, at that temp (assuming the gun got to that temp) stainless is brittle. CM steel is the better choice.
It is possible that the tolerances changed and cold contracted the steel and the chamber was tighter, increasing pressure and thus lowering the threshold at which you experienced pressure signs. If you had water or frost in the chamber, this could cause high pressuring. I suppose the inter-cooler effect could also account for it with air being more dense...
BTW -31 is too cold for using stainless barrels safely, at that temp (assuming the gun got to that temp) stainless is brittle. CM steel is the better choice.
It is possible that the tolerances changed and cold contracted the steel and the chamber was tighter, increasing pressure and thus lowering the threshold at which you experienced pressure signs. If you had water or frost in the chamber, this could cause high pressuring. I suppose the inter-cooler effect could also account for it with air being more dense...
Are you sure stainless gets brittle when It is cold? I use to work with liquid nitrogen and we pumped it through stainless pipe because stainless was the best marerial for handling the cold (-200C ) liquid. This experience was on equipment that saw alot of jaring and pounding. The only reason I brought this up is because I shoot in the extreme cold from time to time and I oppted for a stainless Lilja barrel because I thought it was the best choice out there.
To get back to the thread, I have read that some powders can produce high pressures when they get cold (below -20C if I remember correctly). I have never had any problems in the cold but I try to keep my ammo warmish, in my coat or pocket. I did some shooting before Christmas at -35C to see how my rifle worked and it worked flawlessly but again my ammo was warmish.
To get back to the thread, I have read that some powders can produce high pressures when they get cold (below -20C if I remember correctly). I have never had any problems in the cold but I try to keep my ammo warmish, in my coat or pocket. I did some shooting before Christmas at -35C to see how my rifle worked and it worked flawlessly but again my ammo was warmish.
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I'm sure someone will have had experience with this, but in the mean time:
It is my understanding that the case stays in place mainly due to friction from the shot pressure inside the case forcing it into the chamber walls (and not force from the bolt). If this is true, then potentially the case may have stretched more than normal (leading to sticky bolt lift) as there was less friction between the case and the chamber wall due to the presence of the slippery frost/water/steam.
It is my understanding that the case stays in place mainly due to friction from the shot pressure inside the case forcing it into the chamber walls (and not force from the bolt). If this is true, then potentially the case may have stretched more than normal (leading to sticky bolt lift) as there was less friction between the case and the chamber wall due to the presence of the slippery frost/water/steam.
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- Location
- Somewhere on the Hudson Bay Coast
I don't think that being subjected to the cold is the problem for stainless, the problem is being subjected to the stresses that a barrel is exposed to during firing, at low temperatures. The Krieger web site talks a little bit about stainless vs carbon steel for use in cold temperatures and suggests that carbon steel is a better choice, but I have not seen the suggestion that the use of a stainless barrel in very cold conditions is dangerous. My .375 Ultra has a Smith stainless barrel and I've used it in very cold conditions without problems. My Lilja .243 has also been used in the cold with no ill effects.
Handloads, 308, factory gun, cm barrel.
Some good info on barrel materials and their temperature tolerances...
Carbon Steel: AISI 4140
The material used for most barrels is AISI 4140 Cr-Mo steel. This is one of the most excellent steels produced for engineering applications. This alloy steel contains by wt. %: C 0.4, Mn 1.0, Cr 1.0, and a number of other elements in lesser amounts. This steel, and its popular cousin 4340, are very popular because they have excellent properties and they are very hardenable. Hardenability is a measure of the depth of material that can be hardened during a quenching operation. High hardenability means more uniform strength and possibly faster throughput. This steel can be made fantastically strong (UTS 200 Ksi) and hard (Rockwell C 57). This material is used to make bearing balls, and if you think about it a barrel is basically a bearing, so this makes sense. This steel is easily machined, welded, otherwise handled.
One thing it also does well is oxidize. Carbon steel barrels must be protected from oxidation, since iron oxide (rust) does not form a stable protection layer on the surface like chromium. Typically barrels are "blued", which is the designation for any of the various mixtures of chemicals used to change the color of the steel to a dark blue/grey color. The blue color is actually oxidized iron, but it is Fe3O4, which is a stable layer much like the one that forms on chromium or nickel. Bluing is also done on drill bits, and that is a very high wear application. Blue, or multicolored sheen, can be seen on many heat treated parts such as hacksaw blades. This grows on the surface during heat treating. The color is dependent on the thickness, like a soap film. Bluing is not perfect, and standard Fe2O3 rust can also form on a blued firearm. Parkerizing is a phosphating process very similar to bluing. This finish is matte (black usually) and more durable than bluing, and is preferred by the military for these reasons. Also, since it does not leave a polished appearance, the parts can be beadblasted or sandblasted in preparation, increasing throughput. Incidentally, both of these processes can be done by a hobbiest with a large stainless tub full of boiling water and some chemicals which are easily purchased online.
Stainless Steel: AISI 416
Stainless steels have come a long way in this century, and 416 stainless is one of the best available. It can be heat treated to be very strong (200 ksi) and hard (>50 Rc). It is magnetic (some stainless materials are not, that is all beginning with a 3xx) and easily machined due to a high sulfur content. 416 SS contains (other than iron): <0.15% C, 12.0-14.0% Cr, <1.25% Mn, <1.0% Si, <0.06% P, >0.15% S. It is the high Cr content which makes it rust resistant, because the chromium forms a hard stable oxide which protects the metal. This layer is only a few molecules thick, so it is hardly detectable. The high machinability comes at a slight cost of oxidation resistance. The sulphur also prevents galling and binding which makes this material a good candidate for bearings.
Martensitic (400 series) SS has a marked ductile/brittle transition at cold temperatures. Actually, the jump in properties is right near room temperature, or below depending on what annealed/tempered state it is in. When the material is brittle, it is still strong, it is just more sensitive to cracking and fracture. This is most likely a problem for high impact applications rather than high strength applications. Wear is a complicated combination of strength and hardness considerations, and considering the high speed and shock of the load due to a bullet, firing a stainless rifle in the cold could potentially be a problem
Carbon Steel: AISI 4140
The material used for most barrels is AISI 4140 Cr-Mo steel. This is one of the most excellent steels produced for engineering applications. This alloy steel contains by wt. %: C 0.4, Mn 1.0, Cr 1.0, and a number of other elements in lesser amounts. This steel, and its popular cousin 4340, are very popular because they have excellent properties and they are very hardenable. Hardenability is a measure of the depth of material that can be hardened during a quenching operation. High hardenability means more uniform strength and possibly faster throughput. This steel can be made fantastically strong (UTS 200 Ksi) and hard (Rockwell C 57). This material is used to make bearing balls, and if you think about it a barrel is basically a bearing, so this makes sense. This steel is easily machined, welded, otherwise handled.
One thing it also does well is oxidize. Carbon steel barrels must be protected from oxidation, since iron oxide (rust) does not form a stable protection layer on the surface like chromium. Typically barrels are "blued", which is the designation for any of the various mixtures of chemicals used to change the color of the steel to a dark blue/grey color. The blue color is actually oxidized iron, but it is Fe3O4, which is a stable layer much like the one that forms on chromium or nickel. Bluing is also done on drill bits, and that is a very high wear application. Blue, or multicolored sheen, can be seen on many heat treated parts such as hacksaw blades. This grows on the surface during heat treating. The color is dependent on the thickness, like a soap film. Bluing is not perfect, and standard Fe2O3 rust can also form on a blued firearm. Parkerizing is a phosphating process very similar to bluing. This finish is matte (black usually) and more durable than bluing, and is preferred by the military for these reasons. Also, since it does not leave a polished appearance, the parts can be beadblasted or sandblasted in preparation, increasing throughput. Incidentally, both of these processes can be done by a hobbiest with a large stainless tub full of boiling water and some chemicals which are easily purchased online.
Stainless Steel: AISI 416
Stainless steels have come a long way in this century, and 416 stainless is one of the best available. It can be heat treated to be very strong (200 ksi) and hard (>50 Rc). It is magnetic (some stainless materials are not, that is all beginning with a 3xx) and easily machined due to a high sulfur content. 416 SS contains (other than iron): <0.15% C, 12.0-14.0% Cr, <1.25% Mn, <1.0% Si, <0.06% P, >0.15% S. It is the high Cr content which makes it rust resistant, because the chromium forms a hard stable oxide which protects the metal. This layer is only a few molecules thick, so it is hardly detectable. The high machinability comes at a slight cost of oxidation resistance. The sulphur also prevents galling and binding which makes this material a good candidate for bearings.
Martensitic (400 series) SS has a marked ductile/brittle transition at cold temperatures. Actually, the jump in properties is right near room temperature, or below depending on what annealed/tempered state it is in. When the material is brittle, it is still strong, it is just more sensitive to cracking and fracture. This is most likely a problem for high impact applications rather than high strength applications. Wear is a complicated combination of strength and hardness considerations, and considering the high speed and shock of the load due to a bullet, firing a stainless rifle in the cold could potentially be a problem
Yup, that's the kicker. First 3 shots grouped at 0.448 - 0.308 = 0.140" (which is dumb luck, for me), last two with the sticky bolt lift were 1" and 1.5" away from the group. Don't think it was a variation in the load.
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It has been my experience that most often sticky bolt lift is caused from brass cases that are to long. On the last firing the brass from the cases flow into the throat, engaging the rifling, and cause resistance to bolt lift. Have you tried checking case length? My $0.02
Case was trimmed before reloading and was only 0.002" longer after firing. The case did stretch (become longer) between the head and the shoulder, this I figured as it was hard to extract, but what caused this condition, over pressure or moisture on the case from handling?
You mentioned the last two shots were an inch to 1.5" away...but where did they land? If it was above the group then maybe overpressure is part of the problem. You've ruled out signs of pressure on the primer though.
I would not expect the moisture to mess with the shot placement. (Reading your post again I can see that maybe you were taking responsibility for the placement)
Did you role the case in your fingers before loading? Do you know if the powder was free inside the case and not frozen/stuck against the primer? I usually check mine based on something I read once... the requirement is likely disputed.
Glock4ever
CGN Ultra frequent flyer
- Location
- Edmonton, AB
Sounds like your load might be hot. What wgt powder/bullet? Pressures will be lower in the cold. As a point it is not a good idea to work up a load in Winter/Low Temp - esp if you like to hot rod it. In the summer the loads will get hotter with the warmer temp - esp if the rounds are sitting in the sun.
That was the idea, work up a load for cold weather. My summer load starts to peter-out after -18ish. Idea being able to load and carry rounds suitable for the weather conditions. The load is 150gr interbond, 45.5gr varget and the kicker being a fed 215m primer for better ignition. I did get better ignition but maybe pressure on 2 of 5 shots. I dropped 0.5 grains of powder and off to the range tomorrow for another test. Only problem is the weather is supposed to be nice, so I might just shoot my summer load
I'll be sure of my handling tomorrow, ensure the chamber is clean without oil, rounds without condensation and report what I find.
