RL33 Temperature Regression Thread

[Pdvdh]

When you come in from outdoors in the cold your glasses immediately sweat. Ammo does the same. Ask the guy that tried it and sheared his bolt lugs. Moisture doesn't let the brass grip the chamber walls and goes into bolt thrust. I just thought you should know for safety reasons. He only lost three fingers and was lifeflighted to the hospital to get the bolt removed from his shoulder. Matt

I don't disagree with your above statements. Which is why I shoot rifles to record cold weather MV quickly after I remove them from a freezer into warmer temperatures.

I do disagree with your original statement that significant "sweating" occurs inside of the cartridge casing, thereby affecting and degrading the powder. Because the inside of the casing is sealed from the unlimited amount of moisture that can form on the exterior of the casing or cold barrel.

If an action fails because the chamber walls are moist with water or Slick 50, reducing the friction between the casing and the chamber walls, then the cartridge operating pressures either exceeded book maximum pressures, or the action was defective. Bolt action rifles and ammo are designed such that the bolt lugs resist bolt setback forces in and of themselves, without the assistance of the resistance/friction between the cartridge case and the chamber walls. We don't rely on the brass cartridge casing to resist bolt thrust, or bolt setback forces. We can lube the chamber wall with a light coating of corrosion preventative (say Rem gun oil), which will reduce the friction between the chamber wall and the brass casing more so than water, and the rifle action should never fail shooting ammo loaded to maximum book pressures.

I have experienced excessive pressure signs when I purposely lubed my chamber with lubricant to test for stiff bolt lifts, compared to a dry chamber. And I did experience stiff bolt lift with my .280 AI when I ran that test. But then again, my reloaded ammo is undoubtedly running at higher than maximum accepted pressures.

Sorry if I riled your sense of pride. That wasn't my goal. But I stand by everything I've posted in response to your claim that one needs to be careful about freezing ammo because moisture will form within the gunpowder when the cartridge is then later placed into a warmer atmosphere/environment. That statement would imply that hunting in really cold temperatures, and then bringing unfired ammo back into a warm house, is cause for concern regarding future cartridge performance and reliability. It's not.

 

[Pdvdh]

Any moisture on a chamber wall or outside of a case will increase pressure. I have seen it and I watch it very closely now. Just one of the many reasons I choose to do and temp / velocity testing at ambient temps with the rifle and ammo acclimated to the temp out doors.

Jeff

Hi Jeff,
It doesn't increase pressure generated inside the cartridge. The water on the cartridge case or inside the chamber acts as a lubricant to reduce the friction between the brass casing and the steel chamber. That friction does provide some reduction in the force that the case head exerts on the face of the bolt when the cartridge is fired. If the chamber wall or cartridge case is lubricated with water or oil, or ice, or anything else that reduces the coefficient of friction between the brass casing and the steel chamber wall, the resistance to case head setback against the bolt face is reduced, and the case head does thrust against the bolt face with higher force. Which will produce the same symptoms and indications that would be observed with a dry chamber and cartridge when the cartridge has been loaded to higher/excessive pressures.

Your observations of signs of increased pressure are correct and I have observed them myself. bigngreen brought this to my attention years ago, so I lubricated the exterior of some .280 AI cartridges and fired them, just to see what happened. And I did experience indications of increased pressure, just as if I'd added 2 grains of powder and fired the cartridge in a dry chamber.

However these indications/symptom of increased pressure are just that. They are not increased pressures. Only symptoms of increased pressure. They're caused by increased force applied by the case head against the bolt face, caused not by higher internal case pressure, but by a reduction in the friction between the brass casing and rifle chamber.

If we didn't commonly run our loads up to and over maximum book pressures in order to improve MW, we wouldn't experience this. We stop just shy of pressure indications with a dry chamber, and then the slight increase in case head to bolt face force created with a lubricated chamber presents all the symptoms of excessive pressure. The pressure is no more excessive than the pressure we load to all of the time with a dry chamber.

Hope this makes sense. I'm pretty darn confident in this explanation.

 

[Pdvdh]

Any moisture on a chamber wall or outside of a case "will increase pressure". I have seen it and I watch it very closely now. Just one of the many reasons I choose to do any temp / velocity testing at ambient temps with the rifle and ammo acclimated to the temp out doors.

Jeff

Jeff, perhaps you were meaning and thinking "will increase cartridge case head to bolt face force (or thrust)". If that's what you meant, then sorry for my lengthy response. Paul

 

[Pdvdh]

This was an interesting and educational Thread from back in 2010. I learned some things along the way. Ate a little crow myself... stubbed my toe into my own arrogance...

http://www.longrangehunting.com/forums/f28/known-loads-too-hot-now-why-55934/index3.html

 

[Broz]

Paul, you may very well be 100% correct. Did you chronograph the wet loads? I ask because I observed these symptoms. Ejector marks, some brass transfer and light smear at ejector pin hole. Increased bolt lift that would be consistent with the above. Also higher impacts at distance. I did not chronograph, so my only proof of pressure increase was high impacts on proven loads and drops.

In the end I felt it was bad at any rate. I seen obvious abuse to my rifle bolt and lugs that could change head space of the rifle. So, I choose to stay clear of this condition as much as possible. I should add this was with a rifle that was running inside most commonly shared data is for this caliber. A 338 Lapua with a 300 gr bullet and 2800 fps from a 28" barrel.

Jeff

 

[Pdvdh]

Jeff,
I had to go back to the Thread from 4+ years ago. My memory isn't that good. I did indeed record MV, and as it turned out, MV did not increase, even though symptoms of excessive/increased pressure were noted.

Here's a copy and past from that Thread:

"This casing was slicker than snot on the outside. Almost dropped it on the ground. Velocity across the Oehler 33 was 2936 fps. Velocity across the PACT Pro was 2958 fps. This 2936 fps velocity is in comparison to the 4-shot string average velocity chronographed across the Oehler 33 last weekend of 2941 fps. Last weekend my PACT Pro was hit or miss and didn't give enough data to provide a 4-shot average comparison to today's velocity. But today's velocity data were good to go. The difference in velocities between the two chronographs run right about 20 fps when they're both hitting on all 8 cylinders - the Oehler ~20 fps slower than the PACT. So there was no evidence of any additional pressure based on the muzzle velocity obtained with this soapy-water lathered cartridge."

And here's a link to the Thread, which targets my Post, which was Post #42.

http://www.longrangehunting.com/forums/f28/known-loads-too-hot-now-why-55934/index6.html

 

[Broz]

Paul, good to know Thanks! I still feel it is my best interest to avoid these conditions. I just don't like the extra pressure applied to the bolt. I agree it probably does not exceed the limitations it is designed for, but at the same time I try to not beat on a precision rifles bolt.

Thanks for sharing your results. It looks like you did your homework there.

Jeff

 

[dkhunt14]

phorwath you seem like a really smart fellow but by posting of putting oil on your shell and firing makes you liable if somebody does it and gets hurt. All they got to do is copy your post. Have a nice day. Matt

 

[Pdvdh]

phorwath you seem like a really smart fellow but by posting of putting oil on your shell and firing makes you liable if somebody does it and gets hurt. All they got to do is copy your post. Have a nice day. Matt

Matt,
You still brooding over the fact I identified errant information in your prior post? You're posting like a fella who's had his feelings hurt, and as a consequence, has set upon a mission to inflict some similar level of anguish onto me.

I told you I wasn't on a mission to injure your pride. Guess you couldn't accept that.

I've known many gun owners over the years that leave a light oiling in their bores as a corrosion prevention measure. Never heard of any that damaged their firearms or injured themselves solely as a consequence of a light oil coating left on the surface of their chambers, or down their bores.

I confess I have exceeded the speed limit driving down the highway more than once in my life. I'm not overly concerned about liability I incur should someone else exceed the speed limit as a consequence of having read the prior sentence.

Thank you for your concern, and... I'm still having a nice day.

 

[dkhunt14]

Not I am not brooding over your post. I just don't want to see somebody get hurt. That's funny because I every match shooter I see and every gunsmith cleans his chamber with brake clean or alcohol and dries before shooting. Moisture can get in and out of shells; why do you think the military seals there primers and bullets. Matt

 

[5280yotes]

I started at 75.0 and pushed up to 78.5 showing ejector wipe. My first sign of pressure was a slight shadow on some of my cases at 77.5 grains. My load finished out at 77.0 grains. My initial load testing was done at 110 yards from a bipod with 4 shots printing a .6 MOA group. I then verified drops at 525 with a 2" five shot group on my steel target and then I followed them up with two center of mass hits on milk jugs at 535. I'll probably take it on my bear hunt in a couple weeks to see how it does.

Are you seating close to the lands with the loads?

 

[Ridgerunner665]

I only skimmed through this thread, didn't read everything closely...but I have a small contribution that may be of some use.

It pertains to a 30-06 using H4350, which is an extremely stable powder in that round...the only significant velocity increase came when the rifle itself was cold and hot, below 30 degrees and above 80...it gained 10 fps from 30 to 20 degrees....and lost 10 fps from 80 to 90.

I decided it was the steel causing the velocity changes and not the powder, it had to be because the ammo was kept at a stable temp throughout....may or may not be correct, but it made sense to me based on what I saw.

The load being tested was:

168 Nosler Ballistic Tip
57.5 grains H4350
Lapua brass
CCI BR2 primer
OAL ~ 3.34"
2,850 fps

An extremely accurate load in that rifle...

 

[jonthomps]

Great thread. I've got several pounds waiting on my 300NM build to get completed.